bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cortical fields participating in spatial frequency and orientation discrimination: Functinal anatomy by positron emission tomography
Authors: Gulyás Balázs , Roland Per E. 
Published: May 2005

AbstractWith the purpose of localising those anatomical structures participating in the discrimination of spatial frequencies and orientations of gratings, we measured regional cerebral blood flow (rCBF) changes with positron emission tomography (PET) and 15O‐butanol as tracer in ten healthy young male volunteers. The subjects performed two‐alterative forced‐choice discriminations of pairs of squarewave gratings regarding their spatial frequencies or orientations (spatial frequency and orientation tasks) or pairs of a grating and a two‐dimensional random noise pattern regarding the presence or absence of grating pattern (reference task). In both the spatial frequency and orientation discrimination tasks a widely distributed network of functional fields is activated in the occipital, temporal, parietal, and frontal cortices and in the cerebellum. Spatial frequency discrimination required the activation of more cortical fields than orientation discrimination, and whereas the total volume of activated fields in temporal and frontal lobes were similar in the two tasks, the volumes of activated fields in the occipital lobes as well as in the parietal lobes were about two and a half times larger in spatial frequency discrimination than in orientation discrimination. The two networks of cortical fields were partially overlapping in the two tasks. The findings indicate that the discrimination of spatial frequency and orientation signals engages functional networks of cortical fields widely distributed in the human brain. Whereas both the occipito‐temporal and occipito‐parietal visual pathways are involved in both tasks, the processing and analysis of spatial frequency information activates occipital and parietal lobe regions more extensively than those of orientation information. © 1995 Wiley‐Liss, Inc.
Regional cerebral activity associated with the incidental processing of pseudo‐words
Authors: Frith C. D. , Kapur N. , Friston K. J. , Liddle P. F. , Frackowiak R. S. J. 
Published: May 2005

AbstractIn order to study brain activity associated with “incidental” cognitive processing, regional cerebral blood flow (rCBF) was measured in six volunteers while they monitored a sequence of pseudo‐words (e.g., FLOPE) for the rare occasions when the letters were displayed in blue rather than white. In the control condition, the same pseudo‐word was presented repeatedly. In one experimental condition all 60 pseudo‐words were different, while in the other there were 18 repetitions. Although it was not necessary to “read” the pseudo‐words to perform the monitoring task, subsequent forced choice recognition memory for these stimuli was significantly greater than chance. Furthermore, there were significant differences in blood flow between the three conditions. When different pseudo‐words were presented there was significantly greater activity in brain areas concerned with shape and object identity (extrastriate cortex bilaterally), with visual word form (left inferior temporal gyrus), and with articulatory word form (Broca's area) even though none of this information about the pseudo‐words was needed for performance of the monitoring task. In the condition in which some of the words were repeated, there was significantly reduced activity in the right lingual gyrus. This area may therefore be a possible anatomical locus for repetition priming with verbal stimuli. These results indicate the importance of taking into account incidental processing when designing tasks for functional imaging experiments. © 1995 Wiley‐Liss, Inc.
Spatial registration and normalization of images
Authors: Friston Karl. J. , Ashburner J. , Frith C. D. , Poline J.‐B. , Heather J. D. , Frackowiak R. S. J. 
Published: May 2005

AbstractThis paper concerns the spatial and intensity transformations that map one image onto another. We present a general technique that facilitates nonlinear spatial (stereotactic) normalization and image realignment. This technique minimizes the sum of squares between two images following nonlinear spatial deformations and transformations of the voxel (intensity) values. The spatial and intensity transformations are obtained simultaneously, and explicitly, using a least squares solution and a series of linearising devices. The approach is completely noninteractive (automatic), nonlinear, and noniterative. It can be applied in any number of dimensions.Various applications are considered, including the realignment of functional magnetic resonance imaging (MRI) time‐series, the linear (affine) and nonlinear spatial normalization of positron emission tomography (PET) and structural MRI images, the coregistration of PET to structural MRI, and, implicitly, the conjoining of PET and MRI to obtain high resolution functional images. © 1995 Wiley‐Liss, Inc.
A modality‐independent approach to spatial normalization of tomographic images of the human brain
Authors: Lancaster Jack L. , Glass Thomas G. , Lankipalli Bhujanga R. , Downs Hunter , Mayberg Helen , Fox Peter T. 
Published: May 2005

AbstractA modality‐independent approch for interactive spatial normalization of tomographic images of the human brain is described and its performance evaluated. Spatial normalization is accomplished using a nine‐parameter affine transformation to interactively align and adjust the shape of a subject brain to the reference brain detailed in the 1988 atlas of Talairach et al. A user‐friendly software application was developed using the X‐windows Motif environment to guide the user through this process. This software supports data types from a wide variety of tomographic imagers and produces output in spatially concise formats.The parameters used for spatial alignment and shape normalization are presented and methods to apply them discussed. Where normalization parameters cannot be obtained directly from the image, as with positron emission tomography (PET), methods for estimating them are given. Evaluation of a new four‐landmark method to fit the AC‐PC line in 16 magnetic resonance imaging (MRI) studies indicated an average difference assessed as the distance between the true and fitted AC‐PC line at four locations of 0.82 mm when using a 2‐D weighted fit. The same landmarks were evaluated using lower spatial resolution PET‐like images simulated from the 16 MRI studies. The difference between the PET and MR image volumes following alignment was minimal, with mean rotational differences of less than 0.2 deg and mean translational differences of generally less than 2 mm. Spatial normalization is illustrated for single photon emission computed tomography (SPECT), X‐ray computed tomography (CT), PET, and MR image volumes. Modality‐independent spatial normalization can be consistently and reliably performed with the methods and software presented. © 1995 Wiley‐Liss, Inc.
Motion detection and correction in functional MR imaging
Authors: Jiang Aiping , Kennedy David N. , Baker John R. , Weisskoff Robert M. , Tootell Roger B. H. , Woods Roger P. , Benson Randall R. , Kwong Kenneth K. , Brady Thomas J. , Rosen Bruce R. , Belliveau John W. 
Published: May 2005

AbstractSubject motion present during the time course of functional activation studies is a pervasive problem in mapping the spatial and temporal characteristics of brain activity. In functional MRI (fMRI) studies, the observed signal changes are small. Therefore, it is crucial to reduce the effect of subject motion during the acquisition of image data in order to differentiate true brain activation from artifactual signal changes due to subject motion. We have adapted a technique for automatic motion detection and correction which is based on the ratio‐variance minimization algorithm to the fMRI subject motion problem. This method was used for retrospective correction of subject motion in the acquired data and resulted in improved functional maps. In this paper we have designed and applied a series of tests to evaluate the performance of this technique which span the classes of image characteristics common to fMRI. These areas include tests of the accuracy and range of motion as well as measurement of the effect of image signal to noise ratio, focal activation, image resolution, and image coverage on the motion detection system. Also, we have evaluated the amount of residual motion remaining after motion correction, and the ability of this technique to reduce the motion‐induced artifacts and restore regions of activation lost due to subject motion. In summary, this method performed well in the range of image characteristics common for fMRI experiments, reducing motion to under 0.5 mm, and removed significant motion‐induced artifacts while restoring true regions of activation. Motion correction is expected to become a routine requirement in the analysis of fMRI experiments. © 1995 Wiley‐Liss, Inc.
High‐resolution functional magnetic resonance imaging of cortical activation during tactile exploration
Authors: Boecker Henning , Khorram‐Sefat Darius , Kleinschmidt Andreas , Merboldt Klaus‐Dietmar , Hänicke Wolfgnag , Requardt Martin , Frahm Jens 
Published: May 2005

AbstractCortical activation during tactile exploration of macrogeometric objects was investigated in six healthy individuals with the use of magnetic resonance imaging (MRI) sensitized to changes in cerebral blood oxygenation. Dynamic measurement of task‐related signal alterations were performed at 2.0 T using a rapid gradient‐echo MRI sequence (TR/TE=63/30 ms, flip angle 10°, measuring time 6 s) at high spatial resolution (0.8 × 1.6 mm2). Four contiguous sections (thickness 4 mm) parallel to the bicommissural plane covered the hand area of the primary sensorimotor cortex (M1, S1), the supplementary motor area (SMA), premotor areas (PMA), and superior parts of the parietal cortex (PC). Task‐related activation was determined by correlating signal intensity time courses with the stimulus protocol on a pixel‐by‐pixel basis. In contrast to predominantly contralateral M1 activation, effects in the hand area of S1 were not restricted to the contralateral side but were equally present in the posterior section of ispilateral S1. Furthermore, bilateral responses were encountered in SMA and PC, while observations within PMA remained inconsistent. These findings in single subjects readily demonstrate a highly resolved and interindividually reproducible pattern of cortical activation in relation to exploratory finger movements and associated intergration of somatosensory information. © 1995 Wiley‐Liss, Inc.
Frontal component of the somatosensory evoked potential
Authors: Bötzel Kai , Ecker Christian , Mayer Michael , Schulze Stefan , Straube Andreas 
Published: May 2005

AbstractElectric stimulation of the median nerve at the wrist evokes a series of electric potentials that can be recorded from the scalp or directly from the cortex. These somatosensory evoked potentials (SEP) include a parietal negativity with a maximum 20 ms after the stimulus, which originates in the somatosensory cortex, probably area 3b (Allison et al. [1991a], Brain 114:2465–2503 and Desmedt et al. [1987], Electroenceph Clin Neurophysiol 68:1–19). Thirty milliseconds after the stimulus, a negative potential (N30) occurs at frontal recording sites. Recently it was observed that the amplitude of this potential is altered in patients with dystonia, Parkinson's disease, and Huntington's chorea. It has been argued that the N30 potential stems from cortical areas other than the somatosensory cortex, for example, the supplementary motor area. We used multichannel recordings to investigate the scalp distribution of the N20 and the N30 potentials in healthy subjects. We found that the N20 as well as the N30 potentials were accompanied by a corresponding positivity at frontal and parietal recording sites, respectively. The N20/P20 and the N30/P30 potential fields had a mirrorlike appearance, and both showed a polarity reversal near the central sulcus. This and the results of correlation analyses led us to the conclusion that the N30 generator is located near the central sulcus. © 1995 Wiley‐Liss, Inc.
Cortical surface modeling reveals gross morphometric correlates of individual differences
Authors: Loftus William C. , Tramo Mark Jude , Gazzaniga Michael S. 
Published: May 2005

AbstractAdvances in human neurobiology are now made possible through methods which combine structural magnetic resonance imaging (MRI), three‐dimensional reconstruction, and statistical analysis. MRI‐based reconstruction enables the in vivo quantification of regional cortical surface area (rCSA) while inter‐group comparisons uncover relationships of cortical morphometry with genotype, sex, and developmental abnormalities. In studies on normals we have found strong associations between the rCSA of monozygotic twins as compared to unrelated pairings. Further analysis of this data uncovered significant differences between the male and female twins in left hemisphere rCSA. When these methods were applied to brains of dyslexic subjects and controls, we identified a pattern of differences involving all major subdivisions of both hemispheres. Taken together, these techniques can illuminate structurefunction issues in both normal and diseased brains. ©1996 Wiley‐Liss, Inc.
A PET investigation of implicit and explicit sequence learning
Authors: Rauch Scott L. , Savage Cary R. , Brown Halle D. , Curran Tim , Alpert Nathaniel M. , Kendrick Adair , Fischman Alan J. , Kosslyn Stephen M. 
Published: May 2005

AbstractThe purpose of this study was to determine the mediating neuroanatomy of implicit and explicit sequence learning using a modified version of the serial reaction time (SRT) paradigm. Subjects were seven healthy, right‐handed adults (three male, four female, mean age 26.7, range 18–43 yr). PET data were acquired via the oxygen‐15‐labeled‐carbon dioxide inhalation method while subjects performed the SRT. Subjects were scanned during two blocks each of (1) no sequence (Random), (2) single‐blind, 12‐item sequence (Implicit), and (3) unblinded, same sequence (Explicit). Whole‐brain‐normalized images reflecting relative regional cerebral blood flow (rCBF) were transformed to Talairach space, and statistical parametric maps (SPMs) of z‐scores were generated for comparisons of interest. The threshold for significant activation was defined as z‐score ≥ 3.00. Behavioral data demonstrated significant learning (P < .05) for Implicit and Explicit conditions. Tests of explicit knowledge reflected non‐significant explicit contamination during the Implicit condition. Foci of significant activation in the Implicit condition were found in right ventral premotor cortex, right ventral caudate/nucleus accumbens, right thalamus, and bilateral area 19; activation in the Explicit condition included primary visual cortex, peri‐sylvian cortex, and cerebellar vermis. Activations in visual and language areas during the Explicit condition may reflect conscious learning strategies including covert verbal rehearsal and visual imagery. Right‐sided premotor, striatal, and thalamic activations support the notion that implicit sequence learning is mediated by cortico‐striatal pathways, preferentially within the right hemisphere. © 1996 Wiley‐Liss, Inc.
Clustered pixels analysis for functional MRI activation studies of the human brain
Authors: Xiong Jinhu , Gao Jia‐Hong , Lancaster Jack L. , Fox Peter T. 
Published: May 2005

AbstractConventional t‐statistics and cross‐correlation coefficients are commonly used for analysis of functional magnetic resonance images. The sensitivity of these statistics is usually low because severe Bonferroni‐type corrections are required for multiple statistical comparisons to minimize the false‐positive error. In the human brain, most functional areas are larger in size than a single image pixel, and coactivation of numerous contiguous pixels is expected. The probability of occurrence of clusters due to random noise is small and can be modeled. Cluster size and intensity thresholding can be used to assess statistical significance. Previous cluster analysis strategies used Gaussian models, working best with low spatial resolution images (e.g., positron emission tomography). We present a new cluster analysis model applicable to data with little or even no covariance between adjacent pixels. Computer simulations and phantom experiments were used to verify this strategy. Our new method is substantially more sensitive than both the conventional intensity‐only thresholding (IOT) method and the previous cluster method for signal change less than 6%, with maximum significant enhancement in sensitivity of 12.8 and 3.8 times, respectively. The results obtained from normal volunteers with visual stimulation further confirm the effectiveness of our new approach and show an average increase in detected activation area of 3.1 times over the IOT method and of 1.6 times over the previous cluster method using the new approach. ©1996 Wiley‐Liss, Inc.
Characterising the complexity of neuronal interactions
Authors: Friston Karl J. , Tononi G. , Sporns O. , Edelman G. M. 
Published: May 2005

AbstractThis work addresses the complexity of neuronal interactions, the nature of this complexity and how it can be characterised in real neurophysiological processes. A measure of complexity has been introduced recently (Tononi et al. [1994]: Proc Natl Acad Sci USA 91:5033–5037) that is sensitive to the joint constraints imposed by two principles of brain organisation: functional segregation and functional integration. Functional segregation implies that the dynamics of a cortical area should reflect the multidimensional attributes for which that area is specialised (in other words, regional dynamics should show a relatively high entropy). Conversely, functional integration implies a distributed and divergent influence of every cortical area on the remaining areas (i.e., the overall dynamics should show a low entropy). Our measure is based on the profile of entropies of different sized regions of the brain. Complexity is high when smaller regions have (on average) a relatively high entropy with respect to the entropy of the whole system. This measure is equivalent to the (average) mutual information between all small regions and the rest of the system in question.We have applied this measure to nonlinear simulations and to neurophysiological data obtained with fMRI during photic stimulation. Because patterns of activity in the brain are intermediate between a state of incoherence, with regionally specific dynamics and a state of global coherence, we predicted that simulated nonlinear processes with similar characteristics would have a high complexity. In the language of nonlinear dynamics we hypothesised that the greatest complexity would be found somewhere between high‐dimensional, chaotic behaviour and low‐dimensional, orderly behaviour. Equivalently, using the metaphor of loosely coupled oscillators, we predicted that complexity would be highest in the domain between asynchronous oscillations and global synchrony. This hypothesis was confirmed using nonlinear neuronal simulations. In addition, we demonstrate that the complexity of neurophysiological data is easily measured and can show a significant complexity when compared to suitable control processes. © 1996 Wiley‐Liss, Inc.
New and fast statistical‐thermodynamic method for computation of protein‐ligand binding entropy substantially improves docking accuracy
Authors: Ruvinsky A. M. , Kozintsev A. V. 
Published: May 2005

AbstractWe present a novel method to estimate the contributions of translational and rotational entropy to protein‐ligand binding affinity. The method is based on estimates of the configurational integral through the sizes of clusters obtained from multiple docking positions. Cluster sizes are defined as the intervals of variation of center of ligand mass and Euler angles in the cluster. Then we suggest a method to consider the entropy of torsional motions. We validate the suggested methods on a set of 135 PDB protein‐ligand complexes by comparing the averaged root‐mean square deviations (RMSD) of the top‐scored ligand docked positions, accounting and not accounting for entropy contributions, relative to the experimentally determined positions. We demonstrate that the method increases docking accuracy by 10–21% when used in conjunction with the AutoDock docking program, thus reducing the percent of incorrectly docked ligands by 1.4‐fold to four‐fold, so that in some cases the percent of ligands correctly docked to within an RMSD of 2 Å is above 90%. We show that the suggested method to account for entropy of relative motions is identical to the method based on the Monte Carlo integration over intervals of variation of center of ligand mass and Euler angles in the cluster. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 1089–1095, 2005
Building cavities in a fluid of spherical or rod‐like particles: A contribution to the solvation free energy in isotropic and anisotropic polarizable continuum model
Authors: Benzi Caterina , Cossi Maurizio , Improta Roberto , Barone Vincenzo 
Published: May 2005

AbstractA general formalism for the calculation of cavitation energies in the framework of the scaled particle theory has been implemented in the Polarizable Continuum Model (PCM), contributing to the nonelectrostatic part of the molecular free energy in solution. The solute cavity and the solvent molecules are described as hard spherocylinders, whose radius and length are related to the actual molecular shape, while the solvent density is estimated from experimental data, or from the solvent molecular volume, suitably scaled. The present model can describe isotropic solutions of spherical and rod‐like molecules in spherical or rod‐like solvents, and also anisotropic solutions in which the solvent molecules are oriented in space: in this case, the cavitation energy also depends on the relative orientation of solute and solvent molecules. Test calculations have been performed on simple systems to evaluate the accuracy of the present approach, in comparison with other methods and with the available experimental estimates of the cavitation energy, giving encouraging results. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 1096–1105, 2005
Determination of the gas‐phase acidities of halogen‐substituted aromatic compounds using the silane‐cleavage method
Authors: Wenthold Paul G. , Squires Robert R. 
Published: May 2005

AbstractThe gas‐phase acidities of halogen‐substituted aromatic compounds have been determined in a flowing afterglowtriple quadrupole apparatus with use of the silane cleavage method developed by DePuy and co‐workers [C. H. DePuy, S. Gronert, S. E. Barlow, V. M. Bierbaum and R. Damrauer, J. Am. Chem. Soc., 111, 1968 (1989)]. In this method the relative yields of siloxide ion products produced in reactions of OH− with trimethylsilyl‐ or phenyldimethylsilyl‐substituted aromatic compounds are correlated with the difference in gas‐phase acidity of the accompanying neutral products. Acidities are reported for different ring‐positions in fluoro‐, chloro‐ and bromobenzene, chloro‐ and bromonaphthalene and benzyl chloride. Excellent precision is achieved in most cases, with assigned uncertainties less than 2–3 kcal/mol. Good agreement is obtained between the acidities determined with use of two different types of silane precursor. Halogen‐substitution increases the gas‐phase acidities of benzene and naphthalene by similar amounts (13–14 kcal/mol). The effects on different ring‐positions in benzene and naphthalene are shown to be primarily inductive in nature, falling‐off by a consistent 2.5–3.5 kcal/mol per bond separating the acidic site from the halogen‐bearing carbon in the chlorine and bromine‐substituted systems. Larger effects are evident in the positional acidities of fluorobenzene. The meta and para position acidities of halobenzenes are shown to be linearly correlated with the acidities of the corresponding meta and para halophenols, haloanilines and halotoluenes.