Brain Topography, Volume 11, Number 1, 1998

67

Proceedings

The 9th World Congress of the International Society for
Brain Electromagnetic Topography
October 6-9,1998
Organizer: Norman Moore

Young Scientist Section
Neurophysiological functional tomography in multiple sclerosis and quantification of cognitive impairments - Mientus, S.*, Valdes-Sosa, P.A, Pascual-Marqui,
R.* and Haas, J.* (*Jewish Hospital Berlin, Dept. of
Neurology, Germany; ACuban Neuroscience Center
Havana, Cuba; *KEY-Institute for Brain Mind Research,
Zurich, Switzerland).
Background: Cognitive impairment in Patients with
Multiple Sclerosis (MS) due to the demyelinating process
is a frequently mentioned problem. We set out to elucidate the possibilities of neurophysiological data for quantifying extent and functional background of cognitive
handicaps. Methods: 22 MS patients prior to interferonbeta (IFN) treatment (mean age 31 years) and 18 normal
controls (matched in age and sex) underwent examinations of EEG and ERP (Event Related Potentials) during
a visuo-spatial cognitive test paradigm. Localization andcharacterization of ERP and the respective anatomical
generators as well as functional organization of brain
electric activity, evaluated by means of correlation analysis, were based on the data of a neurophysiological tomography (LORETA/VARETA). Results: Compared tonormal controls patients showed different generatorconfiguration for the P3-wave, the wave that is related totask complexitry and performance. While we could specify two focussed generators for normal controls, oneparietal and one frontal, patients showed parallel to theparietal one a more diffuse frontal generator. In patients
P3-latencies were longer and P3-amplitudes were higher
than in normal controls. The N1, related to selective
attention, was less pronounced in patients. Correlation
Copyright © 1998 Human Sciences Press, Inc.

in brain electric activity of cortical areas was much lessand unspecific developed for patients and showed nosensitivity to repetetive trials of cognitive ...
The difference in early information processing forauditory sensory input in vascular dementia and Parkinson's disease. - Hodumi, A., Hirata, K., Arai, M.,
Kubo, J., Yamazaki, K. and Tanaka, H.* (Department of
Neurology, Dokkyo University School of Medicine;
The KEY institute for Brain-Mind Research, University Hospital of Zurich).
The purpose of the present study is to investigate
whether early information processing for auditory sensory input would be different in vascular dementia (VaD)
and Parkinson's disease (PD). Method: The study was
carried out on 19 patients with VaD, 23 patients with PD
and age matched 20 normal individuals. Four-tones
paradigm was given for the subjects. Twenty percent of
the tones had pitch of 1000 Hz for the target condition,and 70% of the tones had pitch of 2000 Hz for the frequentcondition. In addition, 10% of the tones had pitch of 125
Hz and 500 Hz for the non-target condition. Tones were
presented in a regular sequence via earphones at 1.5 sec
intervals at 80 (500,1000 and 2000Hz) and 90 (125Hz) dB
SPL. The subject's task was to count mentally the target
stimuli. Difference waveforms were constructed by subtracting the average response to standard stimuli fromthe average response to non-target stimuli (N-S), standard stimuli from target stimuli (T-S), non-target stimuli
from target stimuli (T-N). Results: In N-S wave, althoughboth normal subjects and VaD patients showed a negative-going component (N2a) peaking about 196 msec, thelatency of N2a in PD patients was prolonged. On theother hand, in T-S wave, there was ...

68

Estimation of the locations of seizure onset in the scalp
EEC. - O'Neill, N.S., Agapov, V.E., Javidan, M. andKoles, Z.J. (University of Alberta, Edmonton, AB, Canada).
Determination of the onset and focus of an epileptic
seizure based on a visual examination of the scalp EEG is
usually very imprecise. To facilitate this process, wehave developed a quantitative method that enables boththe onset of the seizure to be clarified and the locations of
the responsible sources inside the brain to be estimated.
The method consists of band-pass filtering the EEG toeliminate baseline shifts and artifacts and data dependent
spatio-temporal filtering to suppress pre-ictal background and extraneous ictal activity. It also consists of ageneralized form of the MUSIC algorithm, applied to thefiltered EEG, to estimate the locations of the sources
responsible for the seizure. The head model used in thelocalization algorithm is of a realistic geometry designed
using the method of finite volumes. This presentation
will illustrate both the validation of the method using
simulated EEGs and its application to seizure data obtained from a patient EEG in which the seizure onset was
obscure. It is shown that, after filtering, the seizure onset
is clarified significantly and that plausible estimates ofthe locations of the multiple sources underlying the seizure inside the brain can be obtained. In addition, it isalso shown that examination of the waveforms associated with these sources can suggest how the seizure
activity might propagate from one source location toanother.
ERPs to lexical and object decision tasks: Source localization using VARETA and LORETA methods. - Silva,
J.*, Harmony, T.*, Garcia, L.#, Aubert, E.A, Bosh, J.A,
Fernandez, T.# and Fernandez-Bouzas, A.* (*Centro de
Neurobiologia, Campus UNAM-UAQ Juriquilla;A
Centro de Neurociencias, La Habana Cuba; *Proyecto
de Neurociencias, ENEP Iztacala UNAM).
This paper tries to answer the question whether
pictures and words that name them access a common
conceptual representation or a dual-code representation
for pictures and words. Reaction times and ERPs wererecorded in 15 males young students during lexical andobject decision tasks. With the purpose to eliminate subject's strategies associated to the lexical and object decisions, mediated pairs were used. Mediated pairs arethose words or objects that have an indirect relation
through a third one (e.g., summer and snow are mediatedrelated through winter). The grand averages of ERP to
related and unrelated pairs were computed. A latency
window of 400-450 ms over 20 leads of the 10-20 International System was used for source localization. VARETA
and LORETA were computed for each point of this window. VARETA solutions were projected onto the aver-Organizer: Moore

aged brain provided by the Montreal Neurological Institute. The solutions from both methods were very similar.
There were no differences between the solutions for related and unrelated word-pairs or object-pairs. However
the regions activated during lexical decisions (occipitaland left temporal regions) and object decisions (righttemporal, occipital and left frontal) were different. These
results support the dual-code hypothesis.

Symposium One
Spatial Analysis of Brain Electrical Fields in
Psychiatry
Cognitive evoked potentials in psychiatry: relevance of
topographical analysis. - Strik, W.K., Fallgatter, A.J. andMuller, T.J. (Dept. of Psychiatry, University Hospital
Wurzburg, Germany).
The middle and long latency event-related potentials (ERPs) are considered to be generated by the summary activity of extended and/or multiple cortical dipole
sheets. The quantification of the spatio-temporal brain
electrical field patterns proposed by Lehmann (see:Gevins and Remond, EEG-Handbook, Vol. I; Elsevier
1987: 309-354) allows a robust and meaningful description of the different brain electrical field configurations
related to cognitive processes (e.g., Fallgatter et al., BrainTop., 1997, 9: 295-302) and to subgroups of psychiatricpatients (e.g., Strik et al., Psychiat. Res: Neuroimaging,
1994, 55: 153-166). Furthermore, the reference independent parameters and quantification procedures arefree from interactions between amplitude measures andtopographical map features (Strik et al., Biol. Psychiat.,
1994, 35: 850-856), and unique for the determination oflatencies. The interpretation of these parameters, however, largely relies on indirect validations, such as source
localisation methods in comparison with previous brain
imaging studies (Strik et al., Electroencephal. Clin.
Neurophysiol., in press), or correlations with regional
specific neuropsychological tests (Heidrich and Strik,
Biol. Psychiat., 1997, 41: 327-335). The application of the
topographical analysis of the auditory P300 was succesful to identify distinctive features of psychotic subgroups
in a series of investigations of our group. The results
indicate that different neurophysiological mechnisms areat the basis of schizophrenic subgroups, cycloid psychoses and mania (Strik et al., Acta. Psychiat. Scand., 1993,
94: 471-476; 1996, 87: 179-183; 1998, in press).
Left temporal P300 amplitude reductions in schizophrenia: specificity and relation to cerebral morphology. McCarley, R.W., Salisbury, D.F., Hirayasu, Y., Yurgelun-Todd, D.A., Tohen, M. and Shenton, M.E. (Har-Proceedings

vard Medical School/Brockton VA Medical Center, Department of Psychiatry, Brockton, MA 02401).
Magnetic resonance (MR) measures in schizophrenic (SZ) subjects have revealed structural brain abnormalities, including temporal lobe cortical and limbic
structures. We have shown reduced left superior temporal gyrus (STG) cortical gray matter in chronic SZ, that is
associated with a reduced left temporal scalp region voltage of P300, an event-related potential (ERP) index of thecognitive processing of novel stimuli. However, since
the contribution of chronicity effects to these abnormalities is unknown, and the specificity to SZ vs. affective(bipolar) psychosis (AF) is unknown, we have repeatedthis study in first psychotic episode (FE) patients (first
hospitalization) with AF and SZ. We used high resolution MRI (SPGR, 1.5 mm contiguous slices) and an oddball P300 ERP paradigm in first episode patients withschizophrenia (FE SZ) or affective psychosis (FE AF), andage-, handedness-, and sex-matched control subjects. FE
SZ, but not FE AF or controls showed a left temporal scalp
region reduction of P300 amplitude (Group x Side interactions, N=14 in each group; Arch. Gen. Psych., 1998,55:
173-180.) FE SZ (N=17) showed a reduction in both left
posterior and total left STG gray matter volume compared with FE AF (N=16) and controls (N=18) (Am. J.
Psychiat, in press). In the FE SZ (N=14) there was asignificant correlation between total...
EEG microstates in acute, neuroleptic-naive schizophrenics. - Lehmann, D., Koenig, T., Kochi, K., Hell, D.
and Koukkou, M. (The KEY Institute for Brain-Mind
Research, University Hospital of Psychiatry, CH-8029
Zurich; *EEG-Brain Mapping Laboratory, University
Hospital of Psychiatry, CH-3000 Bern 60, Switzerland).
Brain-electric field (EEG) recordings allow the noninvasive measurement of rapidly changing, global brain
functional states. Using cluster analysis, momentary
EEG field topographies can be sorted into few classes
according to their different spatial configurations. Whilestill explaining most of the variance, this classification
reduces the data to a string of reoccurring, non-overlapping brain functional states, each showing a stable landscape for a short period of time (microstate). Statistics onclassified microstates of spontaneous EEG thus describe
the repertory of brain functional states used during therecording period. For each class of microstates, a mean
duration, a mean number of occurrence per second anda mean spatial configuration is obtained. Under the assumption that schizophrenics differ in their repertory ofbrain functional states already during rest, we analyzed
brain field data from 9 first-break, acute, neuroleptic-naive schizophrenic patients and from two groups of 9matched controls during rest, using four classes of microstates. While during three classes of microstates (80% of69

the time) no group differences were observed, a forthclass showed a significantly different mean spatial configuration and shorter duration in the patients, the duration of this deviant class was systematically shorter withmore pronounced paranoid symptomatology. The deviant class occurred about 3 times per second and covered
about...
Treatment response prediction in psychiatric disorders:using quantitative EEG (QEEG). -Prichep, L.S.*A, John,
E.R.*A, Chabot, R.*, Alper, K.* and Mas, F.* (*New York
University Medical Center, Brain Research Laboratories, Dept. Psychiatry, New York, NY, USA; ANathan S.
Kline Institute for Psychiatric Research, Orangeburg,
NY, USA).
Distinctive profiles of quantitative EEG (QEEG) abnormalities have been reported in many psychiatric disorders. The sensitivity and specificity of QEEG features
have been further demonstrated through the explorationof the electrophysiological heterogeneity within clinically homogeneous diagnostic categories. QEEG features were extracted from 2 minutes of eyes closed
resting, artifact-free EEG recorded from 19 regions, referenced to linked ears. All features were Z transformed
relative to age appropriate normative values. Only aselected subset of extracted features were submitted tothe analysis. Using cluster analysis, subtypes were identified within several populations with DSM-III-R diagnoses including: Obsessive Compulsive Disorder (OCD),
Attention Deficit Hyperactivity Disorder (ADHD), Cocaine Dependence, and Dementia. In each of these disorders, subtype membership was found to be significantly
related to subsequent treatment outcome and/or evolution of the disorder. In most instances, subtype wasindependent of clinical/demographic features anduniquely related to the electrophysiological characteristics of the subtype. Knowledge of the pathophysiological profiles related to treatment responsiveness may
have predictive value across of range of neuropsychiatricdisorders.
Spatial patterns of EEG changes in dementia and theirrelation to disease severity. - Dierks, T.*, Jelic, V.A,
Pascual-Marqui, R.D.*, Wahlund, L-O.A and Maurer,
K.* (*Clin. Neurophysiology, Dept. of Psychiatry I,
Univ. of Frankfurt/Main; A Alzheimer Research Center,
Karolinska Institute, Sweden; #The KEY Institute forBrain-Mind Research, University Hospital of Psychiatry).
Many parameters of EEG like peak frequency, theamount of slow wave and alpha activity are abnormal
and correlate with the severity of cognitive functions in
Alzheimer Disease (AD). However, due to technical limitations conventional frequency analysis does not allow to70draw any conclusions about spatial pattern of brain
physiology. We have quantified spatial EEG alterations
in around 60 patients suffering from Alzheimer diseaseand cognitive impairment using a relative novel analysis
method in the frequency domain (FFT-approximation).
In AD patients, a shift of alpha- and beta-EEG generators
towards frontal brain regions was observed. The amountof this shift correlated with the degree of dementia. The
anteriorization of EEG-generators reflect the pathologicalspatial pattern of glucose metabolism in AD. A similar
spatial pattern of EEG-alterations could be found in asymptomatic family members with genetic AD, suggesting that the spatial distribution of EEG may be used inearly detection of AD.
A topography for anxiety? Distinct maps for different
disorders. - Gerez, M., Tello, A., Nicolini, H. and Serrano, C. (Hospital Espanol de Mexico).
Background: Panic, phobic, obsessive-compulsive(OCD) and generalized anxiety (GAD) disorders constitute discrete diagnostic entities under current psychiatricclassifications. Yet, comorbidity exists and some authors
conceptualize them within a single framework. Purpose:
To study anxiety disorders looking for 1) evidence ofbrain dysfunction, 2) neurophysiological heterogeneity,3) clinical correlations. Methods: 192 unmedicated patients were grouped by DSMIV diagnosis. EEGs wereclassified as normal, diffusely abnormal, focal slowing/epileptiform. QEEGs were inspected for wholehead delta decreases, slow-band increases, or focal
wide-band changes, P300 for abnormal latencies, amplitudes, or focal voltage changes. A focally abnormal record was defined by focal changes in at least two of thefollowing: 1) epileptiform, 2) wide-band power, 3)P300
voltage. MANOVA was conducted. Findings: Epileptiform activity was highly prevalent (35%), and unrelated
to group. Slowing and P300 latency abnormalities were
infrequent (8%). Delta decrease was found in 64% of the
GAD group and 54% of the OCD. Focally abnormal
records were seen in 78% of the patients. Prevalence andlocation were differentially distributed across diagnostic
groups: panic (85%) and GAD (35%) in temporoparietal
areas, OCD (89%) in frontobasal areas predominantly
right. Phobic showed less changes, inconsistently localized. Conclusions: These findings support the hypothesis of brain dysfunction in anxiety disorders. They alsosuggest distinct involvement of brain areas andphysiopathogenesis for different types of anxiety disorders. Results will be discussed in relation to the anatomofunctional literature.

Organizer: Moore

Symposium Two
Pharmaco-EEG
Low Resolution Electrical Tomographic Images of
QEEG subtypes of psychiatric disorders with differential treatment responsiveness. - John, E.R.*A, Prichep,
L.S,*A, di Michele, F.*# and Valdes-Sosa, P.- (*Brain
Research Laboratories, Dept. Psychiatry, New York
University School of Medicine; ANathan S. Kline Institute for Psychiatric Research, Orangeburg, NY; Department of Psychiatry, University of Rome, Tor Vergato,
Rome, Italy; National Scientific Research Center ofCuba, Havana, Cuba).
In multiple international studies, the power spectrum of the EEG has been shown to be predictable andindependent of ethnic background, changing systematically throughout the human life span. This pattern appears to be genetic, regulated by a complex homeostatic
system mediated by many different neurotransmitters.
In the current study we applied low Resolution Electrophysiological Tomography (LORETA) to selected datafrom subtypes of Obsessive Compulsive Disorder, Attention Deficit Disorder, Cocaine Dependence and Dementia patients with different outcomes of treatment or
evolution of illness. LORETA enables a representation of
the generators within the brain which most plausibly
account for the QEEG results. The resolution of this
distributed inverse solution is estimated to be a voxel
about 8 mm or each dimension. An average MRI atlas
was constructed from 300 normals at the Montreal Neurological Institute and the electrode locations defined for
QEEG have been placed in spatial registration with thatatlas. Thus, it is possible to display the inverse solutions
obtained using LORETA on slices from the MRI atlas.
Using this method, the pathophysiological functional
neuroanatomical systems underlying subtypes with different treatment outcome ...
Smoking and the brain function: Combined ERP and
PET studies. - Nagata, K., Yaguchi, K., Kanno, I. andMatsuoka, S. (Research Institute for Brain and Blood
Vessels, Akita, Japan; School of Education, Akita University, Akita, Japan; Showa Hospital, Shimonoseki,Japan).
Combined event-related potential (ERP) and positron emission tomography (PET) studies were carried out
before and after cigarette smoking in normal young volunteers during the continuous performance task (CPT) in
which the subjects were requested to discriminate a single Hiragana. After the abstinence for more than 12hours, the CPTs for the low-demand (LD) or high-demand (HD) paradigms were repeated 6 times. During

Proceedings

the CPT, cerebral blood flow (CBF) was measured repeatedly according to the H215O intravenous bolus injection
method, and normalized CBF images were analyzed by
the 3 dimensional statistical method. Based on 32-channel EEG data, ERPs were averaged and the results weresubtracted between the baseline and smoking conditions.
In the HD paradigms, the amplitude of the positive SEP
components at 260-330 msec became greater after smoking as compared with the baseline, whereas there was no
significant difference in the earlier components before
200 msec. When HD was compared with LD, the CBF
increase in the anterior cingulate gyrus became smaller
after smoking whereas CBF increased in the retrosplenial
cortices including cuneus. The enhancement of the"P300" components after smoking may indicate an activation effect of nicotine.
Low-Resolution Electromagnetic Tomography(LORETA) after representative drugs of the main psychopharmacological classes. - Saletu, B.*, Anderer, P.*
and Pascual-Marqui, R.D.A (*Department of Psychiatry, University of Vienna, Austria;AThe KEY Institutefor Brain-Mind Research, University Hospital of Psychiatry, Zurich, Switzerland).
In a double-blind, placebo-controlled study, EEGs
were recorded in 20 normal subjects aged 23-34 years.
They received at weekly intervals in random order single
oral doses of placebo, the neuroleptic haloperidol (3mg),
the antidepressant citalopram (20mg), the anxiolytic
lorazepam (2mg) and the psychostimulant methylphenidate (20mg). A vigilance-controlled EEG was recorded
from 19 EEG leads before and 1,2,4,6 and 8 hours after
drug administration. For the classical frequency bands,
electrical activity in the brain was localized by means of
low-resolution electromagnetic tomography (LORETA)(Pascual-Marqui et al., International Journal of Psychophysiology, 1994,18:49-65), developed further according
to realistic head geometry based on the Talairach brain
atlas. Thereby the solution space was restricted to cortical gray matter, amygdala and hippocampus, which resulted in 2394 current density values. Statisticalevaluation was based on exploratory t-values. Differences between drug and placebo within a Brodmann area(BA) were considered significant at a global p.05 if at least
50% of the t-values were significant at p.025 (Rueger
procedure). Citalopram, for instance, most typically augmented beta sources, predominantly in the right hemisphere with maximal changes in the temporal (BA 20-22)
and frontal lobe (BA 6); lorazepam reduced theta andalpha rather globally and increased beta locally in BA 6,
an area involved in motor functions. Thus,...
Frontal lobe - motor cortex disconnection syndromes ofchildhood, and the role of methylphenidate in ADHD.

71- Niedermeyer, E. (Sinai Hospital, Baltimore, Maryland,USA).
On the basis of earlier clinical - EEG studies, it has
been assumed (Niedermeyer et al. 1997; Niedermeyer
and Naidu 1997), that - during childhood and early adolescence - the motor cortex requires inhibitory influences
emanating from the frontal lobe. This concept was firstpresented in view of the rare Rett syndrome with mental
deficiency, hypermotility (typical wringing hand movements) and, in 30-40%, epileptic seizures. Massive spiking or theta rhythms over the central region are thought
to represent motor cortex dyscontrol due to an insufficient (anatomically small) frontal lobe. In the course ofadolescence, the frontomotor disconnection loses its significance and some improvement occurs. On a completely nonstructural-dysfunctional basis, frontomotor
disconnection is also assumed to exist in ADHD (attention deficit hyperkinetic disorder) which is quite common (mainly in boys). EEG findings are insignificant;regional blood flow studies have shown decreased frontal lobe perfusion improving after methylphenidate, unfortunately interpreted as vascular disorder (Lou et al.
1984) rather than as secondary phenomenon. There isreason to presume that, in ADHD, the frontal lobe is notdiseased but just "lazy" and in need of a stimulant which
improves both inhibition of motor cortex and prefrontal
selective attention. The methylphenidate effect is hence
logical and not "paradoxical". In Rett syndrome, thefrontal lobe is structurally impaired and hence unable torespond to methylphenidate. Cases of ADHD have to be"pure" and not marred by mistakes ...

Submitted Papers
Word emotional valence influences Steady State Visually Evoked Potential (SSVEP) amplitude and latency
topography. - Silberstein, R.B.*, Robb, D.*, Stanley, R.A,
Burrows, G.A and Pipingas, A.* (*Brain Sciences Institute, Swinburne University of Technology, Melbourne;A
Department of Psychiatry, University of Melbourne,
Melbourne).
We report for the first time, changes in SSVEP topography in the "Emotional Stroop" (ES) task where subjects
identify the colour of words describing emotional states.
Twenty-four right-handed female subjects viewed a series of words that were emotionally negative, positive, or
neutral. The words were presented in one of five possible
colours (red, green, blue, white, purple) and subjects
verbally identified the word colour. Brain electrical activity was recorded from 64 scalp sites and digitized to
16-bit accuracy at 500Hz. EEG was band-pass filtered
0.5Hz-80Hz. The Steady State Visually Evoked Potential(SSVEP) was elicited by a 13Hz uniform visual flicker

72superimposed over the visual fields. Subtracting theneutral word responses from happy and sad word responses revealed the SSVEP changes associated with thespecified emotional valence. Following positive word
presentation, there was a transient SSVEP amplitude reduction at right temporal sites. This effect was larger andextended to left prefrontal and left parietal sites for negative words. Positive words were associated with a transient right prefrontal SSVEP latency reduction of 10 msec
while negative words yielded a transient right prefrontal
SSVEP latency increase of 12 msec. These results point todifferences in right temporal and right prefrontal processes that differentiate between positive and negative
words.
EEG source reconstructions using fMRI constraints. Wagner, M., Fuchs, M., Wischmann, H.-A., Theissen, A.
and St. Willemsen (Philips Research, Hamburg, Germany).
The combination of functional MRI with EEG sourcereconstruction promises to yield both high spatial andtemporal resolution. However, several problematic constellations may occur: EEG sources that do not show up
in the fMRI images; fMRI hotspots without a corresponding EEG source; and a slight displacement between fMRI
hotspot and source location. To overcome these problems for a multiple equivalent current dipole source
model, dipoles are loosely fixed to the fMRI hotspots.
This is achieved by using the hotspots as seeds andkeeping the dipole locations within a maximum distancefrom the seedpoints. Dipole components, timecourses,
and exact locations are fitted. In addition, an unconstrained dipole is fitted to account for EEG data unexplained by the fMRI activity. For distributed source
models, source locations and normals are constrained tothe cortical sheet segmented from anatomical MRI. A
current density reconstruction is performed. In addition
to depth resp. lead field normalization, source locations
are weighted according to their fMRI-induced significances. Different weighting functions may be used, e.g.,derived from thresholded and dilated fMRI hotspots, or
continuous functions of the fMRI maps themselves. Locations without hotspots are downweighted by a factor
of not more than three, else current sources that do notshow up in the fMRI images cannot be reconstructed. The
performance of the proposed methods is demonstrated.
Retest reliability of 3D-LORETA estimates of neuralgenerators of classical frequency bands and changes
after SHTlA-agonists (alnespirone and buspirone) Anderer, P.*, Saletu, B.* and Pascual-Marqui, R.D.A(*Department of Psychiatry, University of Vienna, Austria; AThe KEY Institute for Brain-Mind Research, University Hospital of Psychiatry, Zurich, Switzerland).

Organizer: Moore

Electrical activities in the brain, corresponding todelta (1.5-6Hz), theta (6-8Hz), alpha-1 (8-10Hz), alpha-2(10-12Hz), beta-1 (12-18Hz), beta-2 (18-21Hz) and beta-3(21-30Hz) power of the vigilance-controlled EEG (eyesclosed), were estimated by means of low-resolution electromagnetic tomography (LORETA) (Pascual-Marqui etal. Int. J. Psychophysiol. 1994). In the new implementation
developed by Pascual-Marqui, LORETA is based on arealistic head geometry and solution space is restricted tothe cortical gray matter and hippocampus, resulting in
2394 current density values. For data reduction, LORETA
values were averaged within Brodmann areas (BA),
amygdala and hippocampus. LORETA was applied to
19-channel EEG data, recorded in a double-blind, placebocontrolled study. Twenty young healthy subjects received randomized in weekly intervals single oral dosesof placebo, 1.5,10 and 20 mg alnespirone, a novel selective
SHT1A-agonist, and 20 mg buspirone as reference drug.
Retest reliability between pre-drug recordings was similar
for LORETA and for EEG-mapping values (e.g., alphapower: .61-.87 in different BA; .75-.88 at different electrodes). At the pharmacodynamic peak time (1st hour),alnespirone and buspirone increased theta sources mostpronouncedly in BA 37 (fusiform gyms), and decreased
beta sources most pronounced in BA 10 (superior frontal
gyrus). While the theta increase ...
Event-related synchronization in Parkinson's disease. Diez, J., Ortmayr, B., Pichler-Zalaudek, K., Pfurtscheller, G. and Reisecker, F. (Krankenhaus der Barmherzigen-Brder, Department of Neurology, Graz,
Austria; Department of Medical Informatics, Instituteof Biomedical Engineering, University of Technology,
Graz, Austria).
To study dysfunctions of the cerebral motor system,
such as Parkinson's disease (PD), bioelectrical potentials
associated with the activation of motor areas are of special interest. The aim of this study was to research differences in the EEG between PD patients and healthy
subjects with respect to the post-movement beta eventrelated synchronization (ERS), which is supposed to bean appropriate additional measure in order to investigate
motor dysfunctions. ERS after self-paced, voluntary brisk
movement of the right and left thumb was studied in 17
patients with PD and 17 age-matched control subjects.
The movement-offset triggered EEG data were analyzed
in the 12-16 Hz, 16-20 Hz and 20-24 Hz bands for 8 timeintervals after termination of movement. Significant results were observed in all three frequency bands, indicating notable group differences concerning the magnitude
of post-movement beta synchronization with a strongly
remarkably smaller beta ERS in PD patients. This wasfound as a significant overall main effect for the groups
as well as in interactions concerning side of movement

Proceedings

and electrode positions. When the beta ERS is explained
as a measure of the recovery of the primary motor area
after the termination of movement, our results indicate adysfunction or impairment of the motor area in the ability
to recover in patients with PD.

Symposium ThreeEEG Generators and Brain Anatomy

How the topology of brain areas affects the characteristics of locally generated field potentials (EPs, EEG).
- Lopes da Silva, F.H. (Institute of Neurobiology, University of Amsterdam, Institute of Epilepsy Meer enBosch, Heemstede, The Netherlands).
To understand how field potentials are generated
and how their characteristics can be interpreted it isuseful to construct models of the populations of neurons
properly activated by adequate synaptic inputs. Using
these models the forward problem can be solved, i.e.,
how a given neuronal population causes a specific fieldpotential distribution, in contrast with the inverse problem, of how to estimate the neuronal sources given a field
distribution. With a forward model, where one simulates
the geometry of the neuronal components and the corresponding synaptic activation functions, it is possible tocompute the resulting field potentials, or magnetic fields,
at different sites in the surrounding volume conductor.
In such models the topology of the cortical layers may beconstructed according to realistic anatomical constraints.
Several configurations of dipole layers result in a rangeof different distributions of field potentials from typicalclosed fields to several configurations of open fields. The
specific properties of these fields measured within the
concavity, such as within a cortical fissure, or from thesurface of the convexity of a dipole layer, such as fromthe crown of a gyrus, can be studied in this way. The
biophysical properties of these different configurations
can be studied by explicit models with characteristic
topology as developed in our group by van Rotterdam ...
Functional mapping of eloquent cortex prior to Neurosurgery - do inverse solutions of single equivalent dipoles work? - Harding, G. and Furlong, P. (Clinical
Neurophysiology Unit, Aston University, UK).
Magnetoencephalography (MEG) offers the opportunity to map the functions of the cortex on a millisecond to
millisecond basis. Of all the imaging techniques only electroencephalography (EEG) has similar temporal resolutions. However it is thought that MEG has greater spatial
accuracy than EEG and requires simpler assumptions withregard to the head models. We have carried out pre-sur-73

gical assessment on 13 patients undergoing neurosurgery
at Frenchay Hospital, Bristol, England. For 12 of the patients' assessment of somatosensory and motor locations
were required. All patients underwent assessment using
a 20 channel 2nd order gradiometer MEG system within amagnetically shielded room. A bite bar was used for headrestraint during evoked potential acquisition and also during M.R.I, investigation to allow accurate co-registration(Singh et al. 1997). All patients subsequently underwent
neurosurgery utilising the ISG wand system this providing
accurate feedback of M.R.I. location at surgery. In one
patient's location of visual cortex centres VI & V5 wererequired. Localisation was determined pre-operatively
using an inverse solution of single equivalent dipole with
Monte Carlo analysis providing a 95% probability ellipse.
In all 12 patients requiring somatosensory/motor location
accurate prediction of the central sulcus (confirmed atsurgery) was obtained even when unilateral abnormalities
required transition of Talairach co-ordinates from the otherhemisphere. M.R.I, anatomical location produced locational errors in 20% of the patients. Electrocorticographyof motion VEPs confirmed the accuracy of pre-surgical
MEG location of area V5 in one patient.
Importance of dipole orientation in the evaluation of
focal epilepsy. - Ebersole, J.S. (Yale University Schoolof Medicine New Haven, CT).
Although equivalent current dipoles are a simplistic
model of epileptogenic brain sources, they can provide
important clinical information that is not easily obtainedby traditional inspection of EEG traces. Proper interpretation of dipoles does require an appreciation of theeffects of modeling assumptions. A number of factors
contribute to dipole location inaccuracies, including
source area, synchrony and propagation, and the headmodel. Dipole orientation is more robust and can often
differentiate sublobar sources in brain regions with more
complex cortical geometry, such as the temporal lobe.
The orientation of dipoles also differentiates sources on
the cortical convexity (principally radial orientation)from sources at the brain base or in major fissures (principally tangential). Without dipole modeling (and its
precursor, voltage topography) basal or fissural sources
can be difficult to identify because field maxima do not
overlie the generator region. This can lead to false localization and even false lateralization with standard EEG
review. In summary, dipole modeling is a useful technique for localizing and characterizing spike and seizure
foci, however, dipole orientation must be taken into consideration in order to interpret the model correctly.
Different epileptogenicity in gyral & fissural sources Wong, P. (Dept. of Paediatrics, UBC, Vancouver,
Canada).

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74

There is evidence to suggest that epileptic generators
have different characteristics dependent upon their location within the cortical layer. That is, the epileptogenicity
of a focus is different whether it is located on the gyrus orwithin the fissure. The evidence to support this is from astudy done on central-temporal spikes in children (Gregory and Wong, Epilepsia, 1992, 3(1): 36-44). From 4900
consecutive children, 366 age-matched cohorts were identified, 99 of whom had a tangential dipolar spike field,
while 267 had non-tangential-dipolar field, i.e., a predominantly radial field. The tangential group was foundto have fewer seizures than the radial group (p001). As
well, other clinical parameters were more benign in thisgroup (p001): lower incidence of developmental delay,
higher intelligence or school performance, lower incidence of neurological deficits. The question was why thetangential group would have lower frequency of seizures:conversely, why spike topography would affect seizures.
If the reasonable assumption is made that a radial source
originates from the (exposed) crown of the gyrus, and atangential source originates from the wall of the fissure,then our data suggest exposed gyrus is more epileptic
than fissural wall. Other observations including corticalmapping for speech control, evoked potentials, direct optical reflectometry from cortical surface, as well as sensory-motor organization (homunculus) etc. all suggest
topographic organization of cortical function being adequately and continuously represented on the corticalsurface alone. As the cortical ...

Special Lecture
Working memory, intelligence, and three brain signals.
- Gevins, A. (EEG Systems Laboratory and SAM Technology, San Francisco, CA, 94105).
Current theories of cognition prescribe a close relationship between working memory ability and general
intelligence. In recent high-resolution EEG studies, wefound that increasing working memory load in an n-backstyle working memory task affects a variety of EEG spectral features (Gevins, Smith, McEvoy and Yu, Cerebral
Cortex, 1997, 7: 374-385) and evoked potential components (Gevins, Smith, et al., Electroencephalogr. Clin.
Neurophysiol, 1996,98: 327-348). To test the hypothesisthat these neural signals of working memory relate to
general intelligence, sixty young adults with average tosuperior scores on a standard intelligence test (WAIS-R)
performed working memory tasks concurrent with EEG
recordings. Reaction times were negatively correlatedwith test scores. The amplitude and reactivity of an EEG
spectral feature in the theta band from frontomesial cortex were positively correlated with test scores, as weresignals in the lower portion of the alpha band. The peaklatency of the P3 evoked potential associated with stimulus categorization was negatively correlated with testscores, with a weaker positive relation between P3 amplitude and test scores. Combinations of working memorytask behavioral and neuroelectric variables predicted intelligence test scores with a high degree of accuracy (multiple r = .82). These results indicate a close relationshipbetween general intelligence and the neural mechanismsof sustained, controlled attention used to maintain representations in working memory.

Symposium FourMusic and the Brain
Music and the brain: Evidences from PET and EEG
studies of normal subjects. - Nagata, K., Yoshida, T. andMatsuoka, S. (Research Institute for Brain and Blood
Vessels, Akita, Japan; National Institute of Bioscienceand Human Technology, Tsukuba, Japan; Showa Hospital, Shimonoseki, Japan).
Although music does not directly serve biological
function, a certain functional organization of brain structures has been suggested for the perceptive and/or expressive musical function based on the evidences frompatients with brain lesions. To elucidate the perceptive
musical function in normal subjects, positron emission
tomography (PET) and quantitative EEG were used in theactivation studies music stimulation. By using PET, cerebral blood flow (CBF) was measured in normal volunteers during verbal and non-verbal auditory stimulation.
The narration of Sherlock Holmes story was presented
binaurally as a verbal stimulus, while Mozart's Horn
Quintet was given binaurally as a non-verbal stimulus.
White noise was given during the baseline condition.
During verbal stimuli, CBF increased in both temporal
lobes (transverse and supratemporal gyri) with a left-side
dominant fashion, whereas more symmetrical activation
was observed in the transverse gyri for the non-verbal
music stimulation. In the analysis of background EEG
activity, the 1/f function of the alpha rhythm was compared in normal volunteers during listening to the various kinds of music. There was an increase of 1/f function
when listening to the music including classic music,
whereas no significant change was seen in the 1/f function when listening to rock music.
Effects of musical training and gender on adolescentP300. - Coburn, K., Jocoy, E., Arruda, J., Estes, K. andYagi, Y. (Mercer University School of Medicine, Macon,
GA, USA).
Problem: The empirically measured musical abilityof musically trained males has been reported to decreaseProceedings

significantly during adolescence. This decrease is notseen among musically trained females or among musically untrained individuals of either gender. Methods:
To study possible neural underpinnings of this phenomenon, auditory P300's were recorded from musicallytrained and untrained adolescent males and females performing oddball (pitch discrimination) and missing
stimulus (rhythm discrimination) tasks. Results: P300
latency showed significant effects of task (longer latencies in missing stimulus task), musical training (longer
latencies with musical training), and a task x training
interaction (longer latencies in missing stimulus task,
especially with musical training). P300 amplitude
showed significant effects of task (larger P300's in oddballtask) and musical training (larger PSOO's with musicaltraining), and a training x gender interaction (especiallyamong females). Conclusions: Musically trained adolescent males failed to show any evidence of P300 amplitudeenhancement compared to their untrained cohorts,
though musically trained adolescent females showed theeffect clearly. The absence of P300 amplitude enhancement among musically trained adolescent males may
correspond to their diminished ability to benefit fromformal musical training that has been reported by others.
Comparative EEG mapping story: Saint Exupery versus
Beethoven. - Etevenon, P. (Labortatoire de cartographic
EEG INSERM U320 Caen, France).
Successive 2.56s epochs of EEG recordings and mappings during verbal and musical auditory stimulations
have been obtained. We recorded 16 students in psychology, females, right handed, high alpha subjects, duringrest, hearing a phrase from Saint Exupery and, after that,the beginning of the larghetto movement of concerto in
D major of Beethoven. Recordings of 19 EEG channels(10/20 system, linked ears reference) together with polygraphy (EOGs, EMG) and sound tracks were sampled
and quantified after artifact rejection based on neuralnetwork. These data were analyzed by FFT spectral
analysis and EEG mappings were computed. Dynamic
sequences were recorded on CDROM for multimedia
display of examples of results of one subject. Averaged
results of a sub-group of 6 subjects were statisticallycompared after spectral analysis by Fisher's exact probability tests. Functional activations during verbal stimulation were observed when compared to musicalstimulation. Lower spectral amplitude densities (in microvolts/Hz) were statistically significant (p.05) in alpha(Fp2, Fz, Cz, P4) alpha1 (Fz, Cz, Pz, F4), beta 1 (Cz), beta(Cz, P4) and all over the scalp on theta frequency band(except Fp1, Fp2). Comparisons with previous ERD and
AM-EEG results obtained with the same group of subjects will reveal advantages and inconveniences of increasing time resolution.

75

Submitted Papers
Magnetoencephalography
Attention selectively synchronizes neural responses tocompeting visual stimuli. - Srinivasan, R., Russell, D.P.,
Edelman, G.M. and Tononi, G. (The Neurosciences Institute).
Selective attention is manifested as the capacity tofocus a "spotlight" on a spatial location or feature of avisual scene. In order to investigate neural correlates of
selective attention among competing visual stimuli, we"frequency-tagged" a vertical grating and a horizontal
grating by flickering each grating at a distinct frequency.
At random intervals (2.5 sec), the thickness of the central
bars of both gratings independently increase or decreasefor 3000 ms. The subjects were instructed to attend to one
or the other grating and indicate the direction of changeof thickness with a keypress. On other trials, the subjects
attended to both stimuli, and indicated whether the thickness change of the two gratings was the same or different.
The steady-state magnetic field was recorded during thetrials with a 148 sensor whole-head magnetometer.
Power was detected at both flicker frequencies over occipital, temporal and frontal cortex. When attending to
one of the gratings, the power at the attended frequency
increased while the power at the unattended frequency
decreased. The phase coherence of the MEG signals withthe attended stimulus was selectively enhanced at the
flicker frequency. When attending to both stimuli, thephase coherence of the MEG increased at different sensors for each stimulus. The results suggest that attention
selectively enhances the synchronization of distinct
populations of neurons that respond to each of the competing visual stimuli.
P300 and M300; response changes with probability of
infrequent stimuli. - Boeijinga, P.H., Soufflet, L.,
Liogier d'Ardhuy, X., Toussaint, M. and Macher, J-P.
(FORENAP, Research Institute in Neuroscience,
Neuropharmacology and Psychiatry, Centre Hospitalier, 68250 Rouffach, France).
Counting infrequent acoustic stimuli among repetitive standard tones evokes a P300 scalp potential. We
investigated whether the magnetic component of theintracerebral sources can be detected and localised. MEG
and EEG responses were recorded in 10 healthy volunteers in an auditory oddball paradigm using a wholehead magnetometer (Magnes, BTI, San Diego, USA) and3 scalp-electrodes. Tone-bursts of 2000 Hz were presented randomly, with variable occurrences of 15, 30 or
40%, in a sequence of standard (500 Hz) tones. The
subjects were asked to count silently the infrequent stim-

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76

uli. Averaged sensor-signals equivalent to 28 locations
issued from the international 10-20 system were projected on a 2-D plane and subjected to statistical analysis.
P300 response-amplitudes (between 300-350 ms) werereduced by about 16% with increasing probability. MEG
responses can be characterized by transient deflections
between 70-130 ms, followed by sustained fields between
200-600 ms with maximal values on the decaying phaseof the P300; its topographic distribution shows negativeleft and positive right, possibly coming from structures
underneath lateral parietal or temporo-central corticalregions. The left negativity was significantly reduced forthe 40% condition, compared to that at 15%. The results
indicate that changes in mental activity related to differences in expectancy of infrequent events are clearly reflected in the evoked magnetic responses.

Symposium Five
Vision and the Brain
Learning to see stereograms: Electrophysiology andpsychophysics. - Skrandies, W., Jedynak, A. and Meyer,
M. (Physiological Institute, Justus-Liebig University,
35392 Giessen, Germany).
As we know from our previous studies, the repeatedpresentation of visual stimuli can be followed by lowered
perceptual thresholds. We investigated this kind of perceptual learning with stereoscopic stimuli presented nearthreshold in a combination of psychophysical and electrophysiological experiments. Different visual patterns
were presented as dynamic random dot stereograms(dRDS) in a forced-choice design in order to determine
the thresholds of 16 young normal adults. In addition,
steady state VEPs were recorded from a dense array of 30
electrodes over the occipital areas. In the first half of theexperiment the disparity of the dRDS was below threshold and changed with 6.7 Hz. In the second half of theexperiment the stimuli were above threshold. A final
psychophysical threshold determination proved thatperceptual learning had occurred. In more than half ofthe subjects the thresholds decreased within 30 minutesof stimulation. In these subjects the center of gravity ofthe topographical distribution of evoked activity showeda significant shift towards the right hemisphere. The
other subjects did not show any topographic effects. In
summary, we can show that in most of the subjects adecrease of the threshold of dRDS perception occurs
within a short time of stimulus presentation accompanied by changes in the pattern of activation of neuralelements in the human visual cortex.
Visual evoked potentials and fields: Clinical applica-

tions. - Harding, G. (Clinical Neurophysiology Unit,
Aston University, UK).
Electrophysiological studies of the visual system allow identification of both ongoing potentials such as theElectroocculogram (EOG) and electroencephalogram(EEG), as well as responses evoked by light flashes orpattern changes; electroretinogram (ERG), visual evokedsubcortical potential (VESP) and visual evoked potential(VEP). These potentials have allowed us to study eachlevel of the visual system, either in isolation or as a
combined and integrated study of the entire visual system's response to stimuli. This latter capability has often
proved critical in disease or infancy to identify the site of
the lesion. Recently developments such as the pattern
ERG and the multifocal ERG (or VERIS system) haveallowed more detailed studies of both function and topography of the retina in both normal subjects and patients. The vast studies of the visual evoked potentials of
the 70's and 80's continue but are now joined by the source
localisation power of magnetoencephalography (MEG)
in studies of the visual cortex. The VESP, first reported
by ourselves and Cracco at the beginning of the 80's isnow, in general, accepted as being of subcortical origin
but remains difficult to record, so relatively few studies
have been performed to utilize its ability to reflect activity
at lateral geniculate level.

Symposium Six
Standards for Brain Electrophysiology
Standards for EEG, QEEG, and Evoked Potentials. Duffy, F. (Children's Hospital, Harvard Medical School
Boston University).
Progress in the application of scalp derived electricalsignals to clinical and research issues demands pooling,
not only of scientific expertise, but also muticenter data.
Standing in the way of this are the multiple potential
incompatibilities that arise from the many options that
present themselves to each investigator as data are collected and analytically processed. The development of
an international data collection standard for preliminary
analysis is overdue. The problems and suggested solutions will be presented.
Standards for pharmaco-EEG. - Saletu, B. (Departmentof Psychiatry, University of Vienna, Austria).
Pharmaco-EEG involves the description and quantitative analysis of effects of substances on the central
nervous system (CNS) by electroencephalography (EEG)
and related electrophysiological methods (e.g., ERP,
sleep). Typical questions include if, how, when and inwhich dose a substance acts on the target organ - theProceedings

human brain. Trials may be carried out in phase I in
healthy volunteers and in phase II-IV in patients. In
order to distinguish between drug-effects and phenomena caused by mere random variation, a careful planningof the design, recording procedure and analysis of thestudy is necessary, as described by several IPEG (International Pharmaco-EEG Group) guidelines. Design andplanning issues concern the description of the study subjects and patients (inclusion/exclusion criteria), goals of
the study (e.g., efficacy/safety), data sources (times, locations, variables), study design (parallel group, crossover etc.), multiplicity problems (times, locations,variables, treatments), statistical analysis (confirmatory,
descriptive, exploratory), sample size determination,
methods to avoid bias (blinding and randomisation). As
many factors may affect CNS function, environmental,
situational and personal variables have to be considered
and documented. Within the latter the medical status(state of health, history of prior illnesses, use of drugs,
sleep/wake cycle) plays an enormous role. A medicationfree baseline condition is needed (e.g., wash-out periodof at least 5 times the half-life of the last psychoactive
compound used). Analysis issues such as sample distribution, problems of multiplicity, missing values and protocol violations must be included in the final report.
Standards for dipole localization and alternative approaches. - Lopes da Silva, F.H.*A, Ossenblok, P.*, Pijn,
J.P.A, Velis, D.A and Fuchs, M.~ (*Institute of Neurobiology, University of Amsterdam; AInstitute of Epilepsy
Meer en Bosch, Heemstede;*#EpilepsyCenter Kempenhaeghe, Heeze, The Netherlands; -Philips ResearchLaboratory, Hamburg, Germany).
The sources of electrical or magnetic activity, recorded at the scalp, are commonly represented by equivalent current dipoles (EDs). This is an abstraction, since thereal brain sources never consist of simple current dipoles.
In the simplest cases they may form dipole layers. The
possibility of estimating EDs holds only for brain sourcesthat are rather simple and involve relatively small corticalareas. Examples of these sources are some early components of evoked potentials (EPs) and the initial transient
deflections of epileptiform spikes. In practice such sources
can only be estimated with suficient accuracy in those cases
where rather regular dipolar-like scalp maps are recorded.
However, a common problem encountered in EEG/MEG
analysis of brain sources is that the latter may involve a
number of cortical areas not necessarily contiguous, i.e.,
multiple cortical areas may be active at overlapping timeepochs. Examples of these are the late components both of
EPs and of epileptiform spike-wave complexes, and, ingeneral, event-related potentials. An analysis of thesecases has to go beyond the computation of simple EDs andit must apply alternative methods to estimate the sources77

distributed over the cortex. This can be done using linear
estimation methods applying...

Symposium Seven
New Technology
Frequency domain VARETA for the localization of EEG
sources during attentional tasks. - Harmony, T.*,
Fernandez, T.A, Bosch, }.*, Silva, J.*, Aubert, E.# andGalan, L.* (* Center of Neurobiology and AENEP Iztacala of the National Autonomous University of Mexico;#
Cuban Center of Neurosciences).
In this study we look for differences between EEG
sources computed from EEG segments recorded during
different attentional conditions. Narrow band frequency
analysis of the EEG segments a) previous to the presentation of the stimuli and b) during the task, were performed for two conditions: 1) Task: a difficult mental
calculation operation was visually presented, and 2) Control condition: the stimuli have the same physical characteristics as the arithmetical symbols, but the subjects had
nothing to do. These two conditions were presented in
random order. Ten subjects were recorded. The sources
for each 0.39 Hz were calculated using frequency domain
Variable Resolution Electromagnetic Tomography(VARETA). Sources were projected onto the Average
Brain provided by Montreal Neurological Institute. Repeated measurement ANOVAs for 3 factors (pre or post
EEG segment, condition and the interaction) were computed for each pixel. Significant differences were observed between EEG segments and condition. Theinteraction was very significant at 1.56,2.34,3.12,4.68 and5.46 Hz. These differences were located in frontopolar
regions and in the left hemisphere in frontotemporal,
Sylvian, temporo-occipital and angular gyrus respectively. These areas correspond to those that may be
activated during verbal tasks. This is in agreement withwhat may be expected during mental calculation.
Estimating regional neural activity with the Expectation-Maximization algorithm. - Kiyuna, T., Kamijo, K.
and Yamazaki, T. (C&C Media Research Laboratories,
NEC Corporation).
A new method of estimating regional neural activity
is proposed and investigated using computer simulations. The method estimates probabilities assigned todivided regions within which neural activity is located.
The estimation is conducted by estimating a mixture ofprobability density function (MPDF). The MPDF is defined as the product of regional probabilities of neuralactivity and Gauss' error function which is calculated bysolving the inverse problems at each region. Because theOrganizer: Moore

78

regional probabilities are not directly observable, we employed an algorithm called the Expectation-Maximization (EM) algorithm to estimate them. The algorithm
consists of two steps: (1) Calculate the MPDF by solving
the inverse problems at each region (Expectation step, orE-step). (2) Update regional probability using Bayes'
formula (Maximization step, or M-step). Finally, the
MPDF is maximized by repeating these steps. Computer
simulations using a three-layered (the brain, skull, andscalp) realistic head model showed that during the EM
sequence, two peaks were found in the probability distribution corresponding to two neural activity regions modeled by discrete multiple dipoles. On the other hand, theconventional least-squares method can not find two dipoles because the estimated parameters are completely
disturbed by noise (20% of Gaussian noise was added tothe data in both simulations). These results indicate thatthe proposed method has noise-robustness and can provide clear source images using the probabilistic representation of neural activities.
Topographic study of sleep spindles and SWA byMatching Pursuit - Zygierewicz, J.*, Blinowska, K.J.*,
Durka, P.J.*, Szelenberger, W.A and Niemcewicz, S.A(*Warsaw University; AWarsaw Medical Academy,
Warsaw, Poland).
Transient EEG structures elude the typical methodsof stationary signals analysis. Matching Pursuit offers
high resolution time-frequency description of transientand long-lasting EEG components in one framework.
The method relies on decomposition of signals into basic
waveforms chosen from a large and redundant dictionary, Waveforms are fitted to the signal in an iterative
procedure starting with the function, which accounts forthe highest rate of the signal energy. We have applied
MP decomposition to the 21 - channel whole night sleep
EEGs of 6 normal subjects and 6 patients with insomnia.
As a result of the decomposition procedures all signal
structures were parameterized in terms of frequency,
time occurrence, time span and amplitude. Desired structures were selected by setting the parameters ranges
according to accepted definitions. Then for each derivation different kinds of statistics and distributions wereconstructed e.g. amplitude of spindles as a function of
frequency, histograms of frequencies, time evolution of
spindles and SWA amplitudes etc. We have tested therelationship between SWA and spindles and hypothesisof two topographically different spindles generators, notonly on the basis of the average spectral properties of thestructures, but taking into account coincidences in theirtime occurrence in different derivations and their timefrequency characteristics. The method allows for separation superimposed spindles by accounting for theirspectral and topographical differences. Statistically sig-

nificant differences between studied groups were found.
Automatic registration of MR-images with digitizedhead contours. - St. Willemsen, Fuchs, M., Wagner, M.,
Wischmann, H.-A. and Theissen, A. (Philips Research,
Hamburg, Germany).
An important aspect of multi-modal neuroimaging
is the localization of EEG/MEG sources in relation toanatomical structures extracted from MR-images. Therefore the accuracy of source localization depends on thequality of matching the different coordinate systems.
Whereas most common methods use anatomical landmarks our method works without any predeterminedmarkers or a priori knowledge. Instead the unknown
parameters of the coordinate transformation are determined by fitting the head contour obtained by scanning
the subject with a 3D-digitizer to the skin surface segmented from MR-images. During the fit the overall distance between these contour points and the surface isminimized using a downhill Simplex algorithm. The lackof given point correspondences and the almost symmetric shape of the head lead to some difficulties: Determining the minimum distance between the contour points
and the surface; and the existence of multiple local minima where the optimization algorithm may be trapped.
The first problem is solved by using a distance map
containing the minimum distance to the surface for each
image voxel. To overcome the more difficult second
problem an initial guess for the minimization parameters
is estimated from a coarse exhaustive search over therotation angles regarding a subset of the digitized points.
Furthermore a decoupling of rotation and translation
parameters is applied. The performance of this automatic procedure is demonstrated with different datasets.

Posters
Brain Fields in Psychiatry

Electrophysiology of visual data processing in schizophrenia - Basinska, A. (Medical University of Warsaw,
Poland).
Visual potentials evoked during Continuous Attention Task (CAT) were examined in 50 schizophrenic patients and 50 healthy volunteers. Adaptive segmentation
revealed six microstates following either non-target or
correctly detected target stimulus. For non-target condition the patients, compared to healthy subjects, revealed
lower amplitude of posterior potentials: a positive leftsided and a negative bilateral in segment I (49-138ms)
and II (138-224ms), respectively, and of a positive central
potential in segment V (350-472ms). The latter feature, as
well as delayed microstates III-V (224-472ms), correlated

Proceedings

with CAT errors. Global field power (GFP) in patientswas significantly lower in segments I-II and V in non-target condition, but significantly increased after target
stimulus, while in healthy subjects GFP increased only insegment VI (398-676ms). In patients an increase of GFP
after target (repeated) stimulus in segment II correlatedwith CAT errors. Detection of target in healthy subjects
involved a shift of positive potential in segments IV-V
(268-398) from central towards prefrontal area, while inpatients positive potential persisted in central area andadditionally emerged in frontal but not in prefrontal
location. Those data confirm hypotheses related toschizophrenia: either of hyperarousability on the automatic level or diminished activity in prefrontal regions
during conscious phase of processing. However, an increase of GFP and more posterior location of positive
centroid in segment V during target detection in patients
correlated with shorter reaction time, which suggests
coexistence of compensatory features resulting from engagement of...
Brain function differences between relapsing and abstaining alcohol-dependent patients, visualized by
EEG-mapping and tomography. - Saletu-Zyhlarz,
G.M.*, Saletu, B.*, Lesch, O.M.*, Walter, H.*, Oberndorfer, S.*, Anderer, P.*, Pascual-Marqui, R.D.A and Boening, J.* (*Department of Psychiatry, University of
Vienna, Austria; AThe KEY Institute for Brain-Mind
Research, University Hospital of Psychiatry, Zurich,
Switzerland; *Department of Psychiatry, University ofWuerzburg, Germany).
The aim of the present study was to compare EEG
maps of drug-free, detoxified alcoholics with those of
normal controls and to describe differences between patients relapsing or abstaining during 6 months of relapse
prevention therapy pharmacologically supported either
by flupentixol decanoate 10 mg or by placebo i.m. every
two weeks. Methods: 22 detoxified, drug-free patients(15 males, 7 females) aged 41.5 ± 8.1 years, diagnosed as
alcohol-dependent (DSM III-R: 303.9; ICD-10: F 10.23)
were included in the study and matched with normal
healthy controls. Abstaining patients (n: 12, 9 m, 3 f, age:
39.1 ± 7.6 years) were matched likewise (39.3 ± 8.5 years)
as were relapsing patients (n: 10; 6 m, 4 f, age: 44.3 ± 8.0
years; controls: 44.2 ± 7.8 years). A 3-minute vigilancecontrolled EEG was obtained and analyzed off-line utilizing EEG mapping and LORETA. Results: Detoxified,drug-free alcohol-dependent patients showed, as compared with controls, aberrant brain function characterized by a decrease of delta and slow alpha and anincrease of beta activity as well as an acceleration of thetotal centroid. Most likely these changes reflect a hyperarousal of the central ...

79

Child Psychiatry, Development
EEG coherence in Attention-deficit Hyperactivity Disordered and normal children. - Murias, M.*, Swanson,
J.* and Srinivasan, R.A (*Child Development Center,
University of California, Irvine; AThe Neurosciences
Institute, San Diego, CA).
Attention-deficit Hyperactivity Disorder (ADHD) isa childhood psychiatric disease affecting between 3-8%
of school-aged children. Previous research has demonstrated cortical (including frontal lobe) and sub-cortical(including basal ganglia) abnormalities associated withdopamine transmission pathways in ADHD populations. We investigated whether these abnormalities result in changes in the synchronization of EEG. The
spatial structure of the alpha rhythm in a group of refined
phenotype (ICD-10) attention deficit disordered children
aged 9-11 was examined with dense electrode arrays andcompared to age, gender, IQ and socio-economic statusmatched controls. EEG recordings from 128 channels
were used to determine whether spatial properties of thealpha rhythm are demonstrably different in the patientsvs. normal controls. Measurements of coherence between frontal and occipital sites of each hemisphere wereused to measure the correlation resulting from longrange cortico-cortical fibers oriented along the anteriorposterior direction in each hemisphere. Comparisonswith adults have suggested that these coherences increase in late childhood, and are associated with the
emergence of reciprocal (feedback) connections from anterior to posterior brain areas. These feedback projections are believe to functionally modulated by the activityof the dopaminergic system. The results suggest that theabnormalities of the dopamine transmission pathways in
ADHD populations influence the development of functional interactions between frontal and sensory cortices.
Auditory Evoked Fields in fetal and neonatal magnetoencephalography - Investigations into maturation ofcortical neuronal function. - Olbertz, D.*, Wagner, K.*,
Schleussner, E.A, Schneider, U.A, Huonker, R.#,
Michels, W.A, Scheidt, B.*, Schramm, D.* and Seewald,
H.-J.A (Friedrich Schiller University of Jena, Germany;*Dept. of Neonatology, Jussuf Ibrahim Children's Hospital; ADept.of Gynecology and Obstetrics; *Biomagnetic Centre).
The most sensitive period for brain development
and maturation begins at midpregnancy and continues
until the first month of live. Auditory stimulation activates neurons along the auditory pathway and the cortex.
The latency of auditory evoked response represent thematurity of neuronal functions. Magnetoencephalography is the only non-invasive method to detect such func-

Organizer: Moore

80

tional maturation processes. Great methodical problems
exist in the registration of the very weak fetal biomagnetic
fields. In this study we registrated auditory evoked magnetic fields (AEF) of the fetus in the third trimenon ofgestation and preterm delivered neonates of the same ageof conception (CA). During neonatal or fetal sleep phase
we applicated 500 acoustic signals (1000 Hz, 100 dB, 50
ms, interstimulus interval 1 sec) on the neonatal headrespectively maternal wall directly above the fetal head.
AEFs were recorded over the contralateral hemisphere ina magnetic shielded room using a 31-channel-SQUIDmagnetometer (Philips). After signal processing (average and principle component analyses) we could
registrate cortical AEFs from fetuses (CA 35 weeks) or
preterm babies in the same CA. The latency of the AEF
decreased from 260 ms to nearly ...
Cognition and Emotion
The effects of divided and focused attention on theevoked and emitted auditory P300 - Arruda, J.E.*A#,
Jocoy, E.L.*, Estes, K.M.*, Yagi, Y.*A and Coburn, K.L.*A(*Brain Research Center, Medical Center of Central
Georgia; AMercer University College of Liberal Arts;*Mercer University School of Medicine, Macon, GA,
USA).
The purpose of the present investigation was to examine the relationship between the evoked and the emitted
auditory P300 under conditions of divided and focused
attention. Eleven right handed participants (6 male and 5
female) who reported being free of any neurological or
psychiatric illness performed both an auditory oddballtask and a missing stimulus task under conditions of divided and focused attention. In the divided attention condition, participants were required to simultaneously
perform the Steinberg visual memory task. The task required participants to correctly identify those "probe" images that had been presented previously. Participants inthe focused attention condition were asked to passively
view all images, without making a response. Despite finding differences in the anterior-posterior distribution of the
waveforms, the results of this study suggest that theevoked and the emitted auditory P300 are manifestationsof the same underlying neuronal processes. Althoughsystematically smaller, the emitted P300 amplitudes, liketheir evoked counterparts, were greatly reduced by increased task difficulty. The anterior distribution of theevoked P300 waveform may be due to the presence of afrontal P300a component reflecting the attenrional captureby the rare auditory targets during the active visual task.
Cognitive event related potentials during a learning
task. - EL-Bab, M.F. and Sedgwick, E.M. (Clinical neu-

rological sciences, University of Southampton, UK).
Event related potentials were recorded 34 subjects(age 21-34 yr., 19 male and 15 female) who were trying todifferentiate 200 computer generated patterns into type
A or B. 18 learned better 70% correct judged from the last
50 trials. 16 did not learn to perform better than 55%. Tenother subjects passively observed the patterns. Recordings were from 16 scalp electrodes with linked mastoids
as reference, bandwidth 0.03-30.00 HZ. After the initialvisual evoked potentials there was a widely distributed
long lasting positively, beginning at 200 msec, moremarked frontally and on the right which was not seen in
the passive observers. We averaged the last 25 correct
responses from the learners and not-learners and themean amplitude of the positivity 300-500 msec after the
stimulus is shown from the FZ electrode in the table.
Mean Amplitude at Fz 300-500 msec post stimulus.
Observers (n=10) Non-learners (n=16) Learners (n=18)
1.52 ± 2.32
5.26 ± 2.21
7.39 ± 3.33
p0.002p0.000p0.004

Independent t-test.

The learning process is associated with scalp positivity
which is greater in successful compared with unsuccessful subjects.
A high resolution ERP and PET investigation of verbal
working memory. - Clark, C.R.*, Egan, G.F.A#,
McFarlane, A.C.~, Morris, P.$, Weber, D.* and Sonkkilla, C.#+ (* The Flinders University of South Australia,
Adelaide; A Austin Repatriation Medical Centre, Melbourne; "Howard Florey Institute, Melbourne; -University of Adelaide, Adelaide; $Heidelberg Hospital,
Heidelberg; +Swinburne University of Technology,
Melbourne, Australia).
Imaging studies have shown the various involvementof frontal and parietal structures in working memory function. In this study, PET was used to identify the regions
associated with the storage of verbal working memory
codes. High-resolution ERPs were used to compare theprocessing dynamics associated with the updating of thesecodes and their use in selecting action. Ten normal, righthanded subjects detected visuoverbal targets under fixedand variable target conditions. In the fixed target block,
only a single target had to be memorised. In a variabletarget block, the target to be remembered was updated
frequently. Head and brain structure was determined using MRI. PET was collected using H215O and analysedusing SPM. 124-channel ERPs were collected DC at 250Hz.

Proceedings

The updating of working memory targets was associatedwith bilateral activation of the medial frontal and supramarginal gyri. Scalp activations associated with theupdating of these targets and their use for initiating action
showed similar frontal and parietal topographies. The
processes could be distinguished by key differences in theirtemporal and energy dynamics over successive time intervals in the 100-900ms post-stimulus window.
EEG source differences between correct and incorrect
performance. - Fernandez. T.*, Harmony, T.A, Bosch, J.,
Silva, J.A, Fernandez-Bouzas, A.*, Diaz-Comas, L. andGalan, L. (*ENEP Iztacala and ACenter of Neurobiologyof the National Autonomous University of Mexico).
Several authors have analyzed the relationship between EEG frequency and the performance on different
tasks. In general, a lower EEG frequency has been related
to poor performance. The most common hypothesis wasthat EEG- performance relationship was modulated byalertness level. However, we are interested in EEG-performance relationship when alertness has been maintained throughout the task. This paper shows that in thiscondition, incorrect responses are preceded by different
EEG frequencies than correct responses, and that thesedifferences appear in specific brain regions that participate in each particular task. EEGs were recorded inchildren during three different tasks: Color Discrimination (CD), Verbal Working Memory (VWM), and Word
Categorization (WC). EEG segments previous to thepresentation of the stimulus were analyzed. To corroborate the localization of the EEG activity in each frequency,
the distributed sources were calculated by frequency
domain VARETA, and the spatial distribution of thesources of the EEG previous to correct and incorrect
responses were compared by paired t tests. Incorrect
responses were preceded by lower EEG power values at
7.8 Hz in posterior temporal and right parietal areas in
CDT, 8.59 and 9.36 Hz in frontal areas in VWM, and 10.72
Hz in the left Sylvian region in WC. In the former task
greater 1.56 Hz power in frontal areas previous to ...
Local modulation of alpha rhythm and ERP reflecting
awareness of changes in perceived images in binocular
rivalry - Kobayashi, T. and Kato, K. (Research Institutefor Electronic Science, Hokkaido University, Sapporo,
Japan).
In an attempt to detect cortical activities related tobinocular rivalry (BR), we have measured and analyzed
ERDs (event-related desynchronizations) in the alphaband and also ERPs (event-related potentials). Six
healthy subjects participated in the measurements. Vertical and/or horizontal gratings were presented to the left
and right eyes separately. Subjects were instructed topress a button when perceived images were changed

81

from one image to the other, which triggered data acquisition. As a control experiment, identical vertical (orhorizontal) gratings were presented to both eyes continuously. In this experiment, subjects pressed a button voluntarily at random moments. EEG data of 100 trials were
measured at 20 electrode positions on the scalp in eachexperiment. A clear ERD, i.e., attenuation of variance, in
the alpha band was observed at -250 ms in the left parietal, left posterior-temporal and left occipital areas in BR.
A broad negative ERP component beginning from -400
ms and lasting until 0 ms was also observed in the same
areas in BR. On the other hand, no corresponding ERD
and ERP could be observed in the control experiment.
These findings suggest that the ERD and ERP observedin BR may reflect cortical activities related to awarenessof changes in perceived images.
Selective visual discrimination tasks induce different
cortical activation patterns in dyslectic children. - Lagae, L., Vervisch, J., Hutsebaut, B., Peeters, J. and Verhelle, B. (University Hospital Gasthuisberg,
Department Paediatric Neurology, Catholic University
Leuven, Belgium).
Recent studies have produced conflicting data on a
possible magnocellular visual pathway deficit in dyslectic children. In most studies, only low level visual performance was tested, giving little information about
higher cortical visual processing. We examined if visual
discrimination tasks that activate magno- and parvocellular cortical visual areas, generate different cortical spatio-temporal activation patterns in dyslectic children.
Event related potentials were measured using standard
procedures (32 electrodes) in 14 children with dyslexia,
aged between 8 and 16 years. In a 'form (parvo) discrimination' and a 'position (magno) discrimination' task, children had to select, by pushing a button, a pre-definedvisual target (20% present) in a series of target and nontarget stimuli. Latency and location of the late positive
peak were calculated in the event related potential to thetarget stimulus. In all children, task performance was90%. Latency of the event related positive peak was notstatistically different for the 2 tasks (median parvo
343msec, magno 335msec). Location of the peak was
clearly different. In the form task, the medial central
parietal region was activated, while in the position task,
the posterior parietal region was activated. We conclude
that our magno- and parvo visual discrimination tasks
selectively activate different cortical regions in dyslectic
children, making these tasks highly suitable for comparison with normal children.
Influences of exercise on information processing indifferent sensory modalities. - Yagi, Y., Estes, K.M.* andCoburn, K.L.* (Seinan Jogakuin Junior College, Ki-

82

takyushu, Fukuoka Japan; *Mercer University Schoolof Medicine Macon, GA USA).
Visual reaction time (RT) has been reported to decrease during moderate exercise, and this has been interpreted as reflecting an enhancement of information
processing. This study examined changes in several independent measures of information processing (P300,
RT, accuracy) during exercise, and their relation to visualor auditory modalities. 24 healthy volunteers (mean age
20 + 2 years) performed auditory and visual "oddball"tasks during resting control periods, aerobic exercise periods, and recovery periods. As expected from previous
studies, visual RTs during exercise were significantly
shortened compared to control and recovery periods(which did not differ from each other). We now report ahighly similar shortening of auditory RTs under thesesame conditions. P300 latencies offer independent measures of the speed of information processing unrelated to
motor output. Paralleling the RT changes, auditory andvisual P300 latencies were decreased during exercise,indicating faster information processing in both sensory
modalities. However, both auditory and visual P300
amplitudes were decreased during exercise, suggesting
diminished attentional resource allocation. Also, error
rates were increased during exercise. Taken together,
these results indicate that the enhancement of information processing speed during moderate aerobic exercise,although operating across sensory modalities, is not a
global facilitation of cognition, but is accompanied bydecreased attention and increased errors.
EEG Analysis

Human head conductivity estimation using a Boundary
Element Model. - Eriksen, K.J., Ferree, T.C. and Tucker,
D.M. (Electrical Geodesies, Inc., Eugene, OR 97403).
Accurate individual subject head conductivity estimates are necessary for accurate realistic source modeling results. In order to obtain such estimates we havedesigned a conductivity measurement technique thatmay prove effective for non-invasive measurement ofscalp, skull, and brain conductivity. The basic principle
involves measuring the impressed scalp potentials from
scalp current injection of a microvolt level constant current source. To test this method we have applied it toboth physical models and three human subjects for whichboundary element method (BEM) models were constructed. Simulated annealing was used for optimizationof the unknown conductivity model parameters in order
to increase the chances of finding the global minimum.
For the three compartment physical model with 128
measurement electrodes, our method recovered the conductivity of the scalp, skull and brain with 1%, 3% andOrganizer: Moore

10% errors respectively. BEM models are currently being
constructed for the human subjects. Future work will
extend the method with finite element models that canaccommodate anisotropies, which are known to influence the conductivities of the skull and white matter.
Effect of the numerical forward problem solution errors
on linear inverse solutions. - Phillips, C., Maquet, P. andLuxen, A. (Cyclotron Research Centre, University ofLiege, Belgium).
The 3 sphere shell head model offers an analyticalsolution for the forward problem. Realistic head modelbase on MR images could be more anatomically accurate
but the forward problem can only be solved numerically(e.g., by the boundary element method, BEM): this implies errors depending on the tessellation and numericalapproximation adopted. To solve the inverse problem,the linear inverse solutions (e.g., Loreta, Minimum Norm
[MN], B&G) have been largely used on the 3 sphere shellmodel. These solutions are usually characterised by ablurred reconstructed source distribution and a better
accuracy for superficial sources. On the other hand, themaximal errors of the BEM are found for superficial
sources. With a 3 sphere shell model, the analytical andnumerical (with 2 levels of tessellation and 3 BEM approximations, "linear and constant vertex" and "centre ofgravity" approaches) forward solutions were computed
for a set of 29 electrodes (10-20 system + intermediate).
For each forward solution, the inverse solutions (Loreta,
MN, Weighted MN and B&G) were calculated. The characteristics of these solutions were then studied and compared by means of the analytical forward solution (errorfree). In general, the less error in the forward problem
solution (better BEM approximation and tessellation), theless disturb is the inverse solution. The MN, Weighted
MN and B&G solutions are much more sensitive to theforward solution errors than ...
EpilepsyVideo-EEG mapping - Chavdarov, D., Radionova, M.
and Kojuharov, I. (Alexandrov University Hospital
Sofia, Bulgaria).
Video-EEG is a modern trend in epileptology, but insome cases it is difficult to survey simultaneously thepatients' behaviour and to analyse the ongoing EEG. To
facilitate this process was introduced a simultaneous recording of Video-EEG Mapping. In the EEG Mapping
were used different techniques for better differentiation of
the topographic properties of the discharge from the background activity: series of momentary maps; series ofpower spectra maps; 1st derivative EEG mapping, etc.
The developed mixing programme permits coupling inProceedings

real sequence of time the video and EEG mapping. A slow
motion projection affords an opportunity for better estimation of: 1. The beginning of the discharge and thecorresponding motor activity; 2. The potential distribution and the respective behaviour; 3. The focal activity
masked in the EEG by the bilateral synchronous 3/s complexes, corresponding to adverse movement in patientswith atypical absences; 4. The relation between discharge
area and degree of consciousness (VHS demonstration).
The influence of cortical geometry on the brain maps
from close neuronal sources. - Goncalves, S.*, Silva,
C.*, Foreid, J.P.A and Ducla-Soares, E.* (*Institute ofBiophysics and Biomedical Engineering; ANeurophysiology Service, Portuguese Institute of Oncology, Lisbon, Portugal).
Brain maps are currently used to study epilepsy and,
although they give very accurate information in the time
domain, they don't give quantitative information on thelocation of the neuronal sources that are responsible forthe epileptic activity. For that, we need source localization techniques, either with spherical or preferably realistic head models. In this communication, we process
EEG data for three interictal spikes from a patient withepilepsy, using a dipole model for the source and realistic
head geometry. Both the position and orientation of thefirst source (located in a region of the cortex with few
foldings) were very stable in time. With respect to thetwo other sources, although the corresponding brain
maps were very different, suggesting independentsources, their positions were very close and their orientations varied with time. Moreover, these sources werelocated in a region of the cortex with many foldings.
Since the dipoles that simulate the neural sources areperpendicular to the local surface of the cortex, it issuggested that the stable orientation of the first source
and the important differences in the brain maps of theother two sources are due respectively to the local existence of few or many foldings (as observed in MRI scans).
These results show the importance of dipole localization
models in...
Magnetoencephalography
Time-frequency analysis of somatosensory evoked 600
Hz activity in MEG. - Haueisen, J., Heuer, T. and
Nowak, H. (Biomagnetic Center, Clinic of Neurology,
Friedrich-Schiller-University Hena, Germany).
The origin of the somatosensory evoked 600 Hz
activity is still discussed controversially. The aim of thisstudy is to investigate the distribution of the 600 Hz
activity in the time-frequency domain. Neuromagnetic
fields were recorded with a 31 channel Philips biomag-

83

netometer after electrical median nerve stimulation (0.2ms square pulse, 6000 averages, 4 Hz stimulation rate, 5
kHz sampling rate) in 12 healthy volunteers. Time-frequency analysis was based on Gabor distributions witha frequence resolution of 20 Hz and a time window widthof 8 samples. Dispersion curves were defined by connecting maximum amplitude points in the time-frequency
domain. Our main finding was that the 600 Hz activity
increases in frequency as time moves on in all 12 subjects.
Latency analysis of the single 600Hz activity peaks confirmed this result. The latency difference between earlier
peaks is higher than between later peaks in the 600 Hz
activity. Also, dispersion curves bifurcated in 7 out of 12
subjects, indicating two subcomponents in the 600 Hz
activity. An increase in frequency with progressing time
for a single generator structure producing the 600 Hz
activity is somewhat contrary to the intuitive understanding of the entropy law. Thus, our conclusion is thatthese results support the hypothesis that the somatosensory evoked 600 Hz is produced by a heterogeneous
generator structure.
Localization of equivalent dipole sources of sleep spindles recorded with whole head MEG system. - Manshanden, I., van Dijk, B.W., Kemp, B., Simon, N. andLopes da Silva, F.H. (MEG Centre KNAW, Free University Hospital, Amsterdam and Graduate School of
Neurosciences Amsterdam, The Netherlands).
From animal studies it is known that sleep spindles
are generated by neuronal networks consisting of thalamo-cortical excitatory neurons and inhibitory neuronsof the reticular nucleus. Through reciprocal connections
between thalamic nuclei and corresponding cortical areas, EEG spindle oscillations are generated in the cortex.
There is however very little known about the distributionof cortical sources of sleep spindles in man. In order toinvestigate this, we used a whole-head 155 channel CTF
MEG system. To estimate the functional generators of
sleep spindles we applied, whenever possible, theequivalent dipole source model in spherical and realistic
models of the head. Several types of spindles were distinguished, with frequency components around 13-14
Hz. In most cases the corresponding sources were symmetrically placed in the two hemispheres and formedclusters on the central, parieto-occipital or parieto-temporal regions.
Non-invasive presurgical identification of central sulcus in patients with brain tumors: Comparative MEG
and ECoG investigations. - Nowak, H., Steenbeck, J.*,
Haueisen, J., Huonker, R., Hochstetter, A.*, Haberland,
N.*, Kalff, R.* and Weiller, C.A (Biomagnetic Center,
Department of Neurology, University of Jena, Germany; *Department of Neurosurgery, University ofOrganizer: Moore

84

Jena, Germany; ADepartment of Neurology, Universityof Jena, Germany).
Magnetoencephalography (MEG) is a non-invasive
method to measure evoked cortical activity with a highspatiotemporal resolution. Especially in surgery of
space-occupying pericentral lesions and neoplasms the
localization of the central sulcus is of interest. Dipole
source analysis of somatosensory evoked fields combined with MR imaging appears to be a valuable tool toplan an operation with minimum risk. We recorded SEF
in 20 patients suffering from intracranial tumors. MEGrecordings were performed using a 31-channel biomagnetometer (Philips). We measured SEFs after Medianand Tibial nerve stimulation contralaterally to the lesion.
We localized dipole sources within the early answers of
SEF. Digitally scanned headshapes of patients were fitted and SEF dipole localization's superimposed on MRIslices. It was possible in all patients with brain tumors
to indicate the postcentral gyrus by the SEF dipole aswell as to check the ECoG during surgery. Magnetoencephalography in combination with MRI was shown
to be a valid and reliable method to localize the somatosensory cortex. A precise determination of the relationship between tumor and somatosensory cortex was
shown preoperatively. The combination of magnetoencephalography with the MRI guided neuronavigation
system SMN (Zeiss) leads to an optimal planning ofoperations especially in...
Music
Music Effects on Event Related Potentials. - Arikan,
M.K.*, Demiralp, T.A, Inan, S.A, Oran, O.\ Elhih, M.A
and Uysal, O.~ (Departments of *Psychiatry and Consultation-Liaison Psychiatry, Cerrahpasa Medical Faculty; A Physiology, Istanbul Medical Faculty;#Psychiatry, Istanbul Medical Faculty; "Biostatistics,
Cerrahpasa Medical Faculty, Istanbul University).
Music was hypothesized to exert a calming effect,
and thus reduce distractibility and enhance cognitive
functioning. Musically naive subjects were instructed to
pay attention to one of two different tones. ERPs wererecorded from Oz, O1, O2, Pz, P3, P4, Cz, C3, C4, T3, T4,
Fz, F3, F4, Fpl, and Fp2 in response to task-relevant andirrelevant tone bips superimposed on either white noise,or on instrumental voice of ney (a reed flute played
especially in Mevlevi music). The latencies and amplitudes of four peaks (N1, P2, N2 and P3) were obtained.
The results were tested by a MANOVA design for repeated measures with two factors, background sound (2levels: white noise, ney) and lead (16 levels: Oz O1 O2 Pz
P3 P4 Cz C3 C4 T3 T4 Fz F3 F4 Fp1 and Fp2). The
amplitudes of both P2 (factor: background sound:F(1/4)=6.84; p 0.05) and P3 waves (factor: backgroundsound: F(1/4)=8.34; p.05) increased significantly duringlistening the ney music. There were no significant topographic differences between the two background conditions. Other ERP waves (N1 and N2) did not show any
significant change between the two conditions. Considering the increase of the amplitude of P3 wave that reflects cognitive processing of the sensory input in ...
Pharmaco-EEG
Is information processing mantained during propofol/fentanyl general anesthesia? An ERP topographic
study. - Chiaramonti, R., Ragazzoni, A., Tonelli, M.V.*,
Cecchi, M.A and Zaccara, G. (Unit of Clinical Neurophysiology, Anesthesiology *and Vascular Surgery
ANuovo S. Giovanni di Dio Hospital, Florence, Italy).
Event-Related Potentials (ERPs) were recorded during carotid endoarterectomy (CEA) in order to investigate the efficacy of propofol and fentanyl in inducing andmaintaining a condition of light general anesthesia presumably unassociated with intraoperative awarenessand/or mnesic processes. Auditory ERPs (oddball paradigm) were obtained the day before surgery and during
CEA in 15 consecutive patients (age range 52-83 yrs),
without neurological deficits, fulfilling the criteria for
CEA. 19-channel ERP spline voltage maps were computed off-line in the two conditions and compared. ERP
components N1, P2, P3 were identifiable preoperatively
in all the patients. Intraoperative ERPs showed increased
latencies and reduced amplitudes of all the components:
a clear N1 with a frontal-central distribution was detectable in 60 percent of the patients, whereas an anterior
positive component was observed in response to the rare
tones in 35 percent of the individuals. The scalp topography and the latency range of this positivity resembled
that of a P3a component. A clear central-parietal P3b
was never detected. Based on these findings, a suggestion is made that during the light anesthesia performedin the current study the auditory information processing
was not entirely suppressed and that the electrophysiological counterpart of an early alerting/attentive process (N1/P3a) was maintained.
CBZ induces slow EEG activity in patients with epilepsy. - Radionova, M. and Patroneva, A. (Alexandrov
University Hospital Sofia, Bulgaria).
The data about the degree and extent of distributionof the slow activity induced by CBZ are rather controversial in the different investigations. In our examination
were included 73 patients with simple or complex partial
seizures with or without generalisation, treated with CBZ(Finlepsin - "Asta Medica", Germany). EEG was regis-

Proceedings

tered before and twice during the treatment - on the 30th
and 90th day of the steady state. For quantitative evaluation of the induced changes is used EEG mapping. The
EEG mapping investigation included the distribution of
the normalised power spectra in the standard bands andtheir maximal values and the power distribution of the
focal and paroxysmal activity. In some patients was used
the statistical probability mapping (SPM). In the patientswith diffuse slow activity in the initial investigation no
significant slowing could be stated during CBZ, andthose with severe abnormalities showed even reduction.
From the group of 59 patients with initially normal EEGs
or with slight diffuse changes 35 (63.6 %) show well
expressed increase of the slow activity. The EEG mapping reveals decrease of the alfa power and increase of
the theta power (absolute and normalised). In somepatients the SPUME shows differences up to 6.5 SD localised in the frontal and temporal regions. From the 54
patients with focal (or regional) slow activity in 22 there
was reduction during the treatment. The EEG mapping
reveals decrease of the power of...
Predicting treatment response in narcolepsy using theP300. - Sangal, R.B, Sangal, J.M. and Belisle, C. (Sleep
Disorders Institute, Troy, MI).
In patients with Attention Deficit-Hyperactivity Disorder, P300 auditory amplitude topography predicts
treatment response to stimulants, whereas visual P300
latency predicts response to tricyclics. To evaluate thehypothesis that visual P300 latency (VL) predicts treatment response to modafinil (a new wake-promoting
agent) in patients with narcolepsy, data was analyzed
from a nine week double-blind randomized trial. Patients were 18 to 65 years old men and women with acurrent diagnosis of narcolepsy. 21 patients participated.
14 were randomized to active treatment. All completed
the study. Auditory and visual P300 testing using 31
evenly spaced scalp electrodes, and baseline polysomnograms and objective and subjective tests of daytime
sleepiness, were followed by modafinil treatment.. Testsof sleepiness were repeated at the end of the trail. Good
response was defined as a final Maintenance of Wakefulness Test (MWT).7.3 min (normative sample mean - 3SD), plus an increase 1 SD (3.6 min) over baseline MWT.
A cut-off of 0.5 SE from normal regression constant wasused to separate patients with longer (not necessarily
abnormal) and shorter age-adjusted visual P300 latency(VL). Poor responders had longer age-adjusted 31-electrode mean VL (448.4 ms vs 410.8 ms, p = 0.024). Poorand good responders did not differ on any other baseline
clinical variable. Shorter age-adjusted VL predicted
good modafinil response, with specificity of 0.71 andsensitivity of 0.86.

85

Source Localization
EEG source spectra in brain lesions. - FernandezBouzas, A.*, Harmony, T.A, Silva, J.A, Bosch, J.#, Aubert,
E.#, Fernandez, T.*, Valdes, T.#, Marosi, E.* (*ENEP Iztacala and ACenter of Neurobiology from the National
Autonomous University of Mexico; "Cuban Center of
Neurosciences).
In previous papers we have provided some experimental support for the hypothesis that in the presence ofbrain lesions, delta and theta activities are mainly related
to the volume of the lesion and the edema respectively.
VARETA is a variant of Distributed Solutions to theinverse problem, which imposes different amounts ofspatial smoothness for different type of generators andrestricts current sources to gray matter. In this paper wereport the results obtained with VARETA in 13 patientswith space occupying lesions and 13 patients with brain
infarcts, in order to: 1) Test the accuracy of VARETA forthe localization of brain lesions, and 2) To provide further
support for the origin of delta and theta components inpresence of lesions with vasogenic and cytotoxic edema.
In all patients, log transformed source spectra were compared with age matched normative values, defining theZ source spectrum. Maximum Z values were foundwithin the delta band (1.56 to 3.12 Hz) in 10 patients withspace occupying lesions and in 9 patients with brain
infarcts. The spatial extent of the sources correspondedwith the locations of the lesions. In patients with large
volumes of edema maximum Z values were between 4.29
and 5.12 Hz. Those patients in whom the maximum
abnormality was in...
Error analysis for multisphere approximation in EEG
forward and inverse problems - Greenblatt, R.E.
(Source Signal Imaging, Inc., San Diego CA USA).
Multisphere approximations (which assume a different equivalent sphere for each electrode or magnetometer) have been proposed as a method to improve theaccuracy of M/EEG forward calculations by incorporating head shape information in a computationally efficientmanner. Because the sphere radius is used explicitly inthe electrical case, brain regions distant from an electrodesite may be excluded from the sphere interior for thatelectrode. Using a 3 shell boundary element model(BEM, 512 triangles/surface) derived from an individual
MRI and a uniformly distributed dipole array (n=552,
2cm spacing) restricted to the brain volume, we obtained
the BEM lead field matrix. The multisphere approximation was calculated as the effective sphere origin for eachof 128 electrodes by a least squares fit to the lead field.
Using this multisphere approximation, we found that
nonlinear dipole fitting to the same dipole set resulted in86

a mean localization error of 8mm rms (range 0.4-41 mm).
The largest errors were attained with dipoles near thecenter of the head and close to the inner skull boundary,although these regions were overlapped by all equivalent
spheres.
P300 source localization using LORETA. - Soufflet, L.,
Boeijinga, P., Toussaint, M. and Macher, J-P.
(FORENAP, Centre Hospitalier, 68250 Rouffach,France).
LORETA (Low Resolution Tomography) is one of
the most promising source localization techniques. Developped by Pascual-Marqui since 1994, the method is a
generalized minimum norm algorithm with smoothness
properties working without any a priori assumptions
about the sources. We have used this technique in orderto localize the sources of P300 auditory component on alarge database of 160 healthy volunteer subjects (aged18-41 years (25.5 years ± 4.9); 152 men (142 right-handed
and 10 left-handed), 8 women), selected for presenting
well defined P300 peaks above 10 mV. Recordings havebeen made using 28 EEG electrodes including the 19
electrodes from the 10-20 system. Calculations were performed using a 3 spherical shell model of the head witha grid of 1021 regular points located inside the brain.
LORETA solutions have been computed for each subject
at the latency corresponding to the maximum of the P300
component (315 ms ± 24) and have then been averaged
over all subjects. Our averaged results have shown thepresence of 4 sources, a deep source (frontal and slightly
shifted to the left), one mid-occipital source and twolateral and symmetrical sources (the left source being
predominant). The deep source could correspond to thesource located in the hippocampus postulated by many
investigators such as Tarkka et al. (1995). The lateralsources could be explained as a residual of bilateral auditory sources. The occipital source is not yet ...
Dipole model-based detection of focal interictal EEG
events. - Van Hoey, G.*A, Vanrumste, B.*A, Boon, P.*,
D'Hav, M.* and Lemahieu, I.A (*Epilepsy Monitoring
Unit, Department of Neurology, University Hospital of
Ghent; AElectronics and Information Systems Department, University of Ghent).
Introduction: We present a method for the detectionof interictal epileptic EEG spikes, based on a dipole
model of the underlying source. The aim is to detect only
those interictal phenomena originating in a focal irritative zone, while imposing as few constraints as possibleon the precise shape of their waveforms. Additionally,
the method will provide an estimate of the corresponding
source location for each detected event. Methods: Foreach position of a moving time window the validity of asingle spatio-temporal dipole model is evaluated by cal-

Organizer: Moore

dilating a RRE (relative residual energy) measure. A
detection is made for each window position yielding a
RRE lower than a certain percentage. The corresponding
EEG is then considered to have a focal underlying sourceof which the dipole parameters provide an estimate oflocation and orientation. The method was applied to the
EEG of epilepsy patients during long-term video-EEC
monitoring, using both a three-shell spherical headmodel and a finite difference realistic head model. Results and discussion: The method is capable of detecting
and localising most of the focal epileptic spikes present
in the EEG, while the number of false-positive detections
remains acceptable. Furthermore, the detected spikes
can be distinguished from false detections (e.g., eyeblink
artifacts) on the ...
Reciprocity and lead fields used in the numerical inverse procedure of EEG source analysis. -Vanrumste,
B.*A, Van Hoey, G.* A , Boon, P.*, D'Hav, M.* and Lemahieu, I.A (*Epilepsy Monitoring Unit, Department of
Neurology, University Hospital of Ghent; A Electronics
and Information Systems Department, University of
Ghent).
Introduction: In EEG source analysis numericalmethods utilizing volume elements instead of surface
elements have been difficult to use in the inverse procedure due to the large number of nodes and the numberof forward calculations needed to perform a dipole fit.
Yet the possibility to incorporate several tissues with a
specific conductivity can lead to more precise localizationof the electrical activity. Furthermore the potentials at
depth electrodes can also be studied. We present a
method to perform the inverse problem with only alimited number of forward calculations using lead fields,
the reciprocity theorem and the finite difference method(FDM). Method: The potentials at the scalp electrodes are
obtained using the analytical expression in a three-shellconcentric spherical head model (with radii of 100,90 and
80 mm) for dipoles located on the line connecting thecenter of the spheres and the right ear and orientatedalong the three axes. These potentials are brought into
the inverse procedure. In the inverse procedure the forward evaluations will be performed numerically using
lead fields generated between the two lead electrodes andthe reciprocity theorem introduced by Helmholtz. The
number of forward calculations is reduced to the numberof electrode pairs...
Localization of the epileptic focus in patients withknown (MRI) lesions with Low Resolution Electromagnetic Tomography. - Worrell, G., Brinkmann, B.,
Busacker, N., Lagerlund, T., O'Brien, T. and Sharbrough, F. (Division of Epilepsy and Department of
Neurology, Mayo Clinic, Rochester MN 55005).

87

Proceedings

Patients with medically intractable pa trial epilepsy
and well defined MRI lesions were studied using Low
Resolution Electromagnetic Tomography (LORETA) toinvestigate the potential of this method for accurate intracerebral ictal source localization. Patients admitted tothe epilepsy monitoring unit with MRI lesions and partial
epilepsy were studied using 31-electrode scalp EEG. A
finite element model of the scalp, skull and cortex was
obtained from the patients MRI. The scalp electrodes andpatients head shape were digitized, and then co-registered with the MRI. The co-registration of scalp electrodes and MRI renders the precise location of scalp
electrodes relative to brain parenchyma and provides arealistic model for the electromagnetic inverse problem.
The compressed special array of the ictal EEG was used
to identify the dominant ictal frequencies. Phase encoded FFT spectral analysis was used to obtain a scalp
potential map (Lehmann et al. 1990). The scalp potential
map was then analyzed using LORETA to obtain tomographic maps of the generations of the ictal EEG discharge. A commercially available package (Source Single
Imaging) that utilizes a finite element solution was used
for the inverse solution. The correspondence of the
LORETA derived ictal current sources with the patient's
MRI lesion was determined by co-registration of the current source tomograms and the MRI.
Classification of the scalp EEC during normal cognitive
activity based on the locations of equivalent dipole
sources. - Lind, J.C.*, Flor-Henry, P.* and Koles, Z.J.A(*Alberta Hospital Edmonton; AUniversity of Alberta,
Edmonton, AB, Canada.
Knowledge of the source distributions underlying theEEG during normal cognitive activity would help to clarify
functional organization of the brain. To test this hypothesis, 43-channel EEGs were recorded from 70 female volunteers during eyes open and eyes-closed (passive)
conditions and during word-finding and dot-localization(active) exercises. EEGs were Fourier transformed, divided into training and test sets and classified using thecomplex frequency domain generalization of the classicaltwo-group quadratic discriminant function. Inputs to theclassifier were obtained by factoring the spatial cross-spectral matrix into patterns common to the two passive EEGs
and to the two active EEGs. Using only two spatial patterns, 84% of the passive test-set EEGs were correctly classified while using six common spatial patterns, 74% of theactive test-set EEGs were correctly classified. The MUSIC
algorithm was used to estimate the locations of the equivalent dipole sources that best accounted for the spatial patterns in each classification. Using the potential scalp
images generated by these sources, 82% of the passive and
57% of the active EEGs were correctly classified. Sourcesthat distinguished the passive EEGs were focused andlocated in the central posterior - right frontal regions whilesources that distinguished the active EEGs were diffuse
and located in right posterior - left frontal regions.
Visual and Sensorimotor Systems
The characteristics of two negative peaks on visualevoked potentials with depth perception. - Miyawaki,
Y., Hayashi, R., Yanagida, Y., Maeda, T. and Tachi, S.
(Department of Mathematical Engineering and Information Physics, The University of Tokyo, Japan).
It has been known that the peak latency of the negative potentials in occipital region evoked by random-dot
stereogram stimuli was about 200msec. Generally, inthese experiments, stimuli were displayed in small visual
field (about 14.3 X 11.1 degree) using devices such as
CRT. We used wider visual field of about 40 degrees witha LCD projector and screen and found out the two negative peaks whose latencies were 180 msec and 280 msec,
respectively. To identify the main factor of these peaks,
we controlled two features of shape and disparity, which
are essential for depth perception by random-dot stereogram stimuli. It was suggested that the first peak mainly
resulted from response on early visual processes, and thesecond peak mainly resulted from response on higher
visual processes related to depth and shape perception.
Next, we estimated the effect of stimulus size by changing
3 parameters: background area, target area (part of including disparity) and the ratio of target to backgroundarea of stimuli. In Result, each peak showed different
response tendency and the above hypothesis was alsosuggested here. Furthermore, by dipole tracing method,
we attempted to localize active sources to explore thetransition from the first peak's state (early level) to thesecond peak's state (higher level).
New Technology
Measurement of EEG electrode lead fields using Current Density Imaging with MR? - Joy, M.L.G., Kusano,
M. and Henkelman, R.M. (Institute of Biomedical Engineering, Sunnybrook Health Science Center, University of Toronto, Toronto, Ontario, Canada).
We have developed a technique, Current Density
Imaging (GDI), that allows electric currents to be imaged
with clinical Magnetic Resonance Imagers. The method
has been used in rabbits to image bipolar 40 ms current
pulses. It has also be used to image Radio Frequency (RF)currents in phantoms and the human leg. A possible
application of these methods is to measure the lead fieldsof EEG electrodes. Our hypothesis is that Solutions of theinverse problem of the EEG, based on lead fields measured directly by CDI, will be more accurate than those88

based on a head model constructed using assumed tissue
conductivities and simplified geometry. We will support
this hypothesis by showing CD images which demonstrate the significant effect of the CSF and other structures
on current pathways in the brain. These images also
show the current signal to current noise ratios which areachievable with GDI. We will show how the RF CDI
technique could be used to gather 20 lead fields in one
hour of imaging. We will also describe work in progresson an electrically accurate MR head phantom with which
we plan to test our hypothesis.
Complex permittivity measurements during corticalspreading depression - study for RF-CDI. -Yoon, R.S.
and Joy, M.L. (Institute of Biomedical engineering, University of Toronto, Toronto, Canada).
Radio-Frequency Current Density Imaging (RFCDI) is a new imaging technique which measureschanges in current density concomitant with changes in
conductivity. RF-CDI could provide a three-dimensional
functional data with better spatial and temporal resolution than the currently available techniques such as PET

Organizer: Moore

or BOLD imaging. For RF-CDI's to be used as a brain
tomography tool, it requires an activity-dependant conductivity change in the brain. To examine the changes incomplex conductivity in the brain, we conducted measurements in the rodent neocortex during spreading depression phenomena. Spreading depression was chosenbecause of relatively well known behavior and its many
similarities to migraine headaches and ischemia. The
measurements were made using a coaxial probe technique. In almost all cases, spreading depression caused
two types of change in the conductivity measurements.
An increase in conductivity with a short latency (30~60s;
15-30 mm/min) was followed by a large increase with alonger latency (200~300s; 3-4.5 mm/min). The magnitude of changes were in the range of 3% to 20% in conductivity and 9%~40% change in dielectric constants.
Although the exact mechanisms of spreading depression
is not well known, these large changes in conductivity
measurements show that RF-CDI is a viable approach tothe study of spreading depression and other similar brain
activities such as ischemia and migraine with aura.