bluuebunny/crossref_metadata_2025_split huggingface dataset:
Distinct Cortical Activation Patterns during Long-Term Memory Retrieval of Verbal, Spatial, and Color Information
Authors: Rösler Frank , Heil Martin , Hennighausen Erwin 
Published: February 2008

Abstract
Slow, DC-like event-related brain potentials (ERPs) were recorded from the scalp of 30 healthy young adults to test the hypothesis that distinct cortical areas are activated when different types of information are retrieved from long-term memory. Three groups of 10 subjects each were first trained with associations between either pictures and spatial positions (spatial condition), pictures and color patches (color condition), or nouns and nouns (verbal condition). All three experimental conditions were completely analogous with respect to the established associative structure, the learning procedure, the performance criterion, and the retrieval test that followed 1 day after learning. Slow event-related brain potentials being recorded during retrieval had a significantly distinct topography. The maximum of a DC-like negative wave was found in the verbal condition over the left frontal, in the spatial condition over the parietal, and in the color condition over the right occipital to temporal cortex. These results are consistent with the idea that memory representations are either “down-loaded” into or directly reactivated within those cortical processing modules in which the same material was handled during perception. Response times, on the other hand, revealed no difference between the three retrieval conditions. In each case RT increased monotonically, if more items had to be scanned. Thus, while the ERPs suggest the involvement of different cortical processors during memory search the response times suggest that a sequentially operating scanning mechanism applies to all of them.
Separate Representation of Stimulus Frequency, Intensity, and Duration in Auditory Sensory Memory: An Event-Related Potential and Dipole-Model Analysis
Authors: Giard M. H. , Lavikahen J. , Reinikainen K. , Perrin F. , Bertrand O. , Pernier J. , Näätänen R 
Published: February 2008

Abstract
The present study analyzed the neural correlates of acoustic stimulus representation in echoic sensory memory. The neural traces of auditory sensory memory were indirectly studied by using the mismatch negativity (MMN), an event-related potential component elicited by a change in a repetitive sound. The MMN is assumed to reflect change detection in a comparison process between the sensory input from a deviant stimulus and the neural representation of repetitive stimuli in echoic memory. The scalp topographies of the MMNs elicited by pure tones deviating from standard tones by either frequency, intensity, or duration varied according to the type of stimulus deviance, indicating that the MMNs for different attributes originate, at least in part, from distinct neural populations in the auditory cortex. This result was supported by dipole-model analysis. If the MMN generator process occurs where the stimulus information is stored, these findings strongly suggest that the frequency, intensity, and duration of acoustic stimuli have a separate neural representation in sensory memory.
Agrammatism: Behavioral Description and Neurobiological Explanation
Authors: Pulvermüller Friedemann 
Published: February 2008

Abstract
Subjects with brain damage resulting in agrammatic aphasia frequently omit or substitute function items (function words and inflectional affixes). However, they show only mild deficits in using meaningful content words. Agrammatics' performance on comprehension tests reveals a rather complex pattern. They usually understand active sentences correctly, but perform on chance level on passives. The same contrast is observed for more complex sentence types, such as subject vs. object clefts or relatives. This complex comprehension pattern suggests that agrammatism is a syntactic disturbance that selectively affects particular sentence structures. Nevertheless, it is possible that both the production and comprehension patterns go back to an access problem for grammatical morphemes. If an agrammatic aphasic comprehends only 50% of these morphemes, she or he may well be problem-free in understanding the resulting “pruned” active sentences in which some of the grammatical morphemes are missing. In contrast, she or he is likely to arrive at the wrong meaning when confronted with “pruned” passives. This hypothesis raises the question of how fully competent speakers interpret ungrammatical “pruned” strings derived from well-formed sentences by systematically deleting function items. Experimental data demonstrate that competent speakers approximate the agrammatic comprehension pattern when being presented with “pruned” strings. This argues that agrammatism can, indeed, be viewed as a deficit in processing function words and inflectional affixes, which may manifest itself in production and/or comprehension tasks. Assuming that cortical cell assemblies with distinct topographies correspond to content words and grammatical morphemes, it is possible to explain agrammatism in terms of lesions to these neuronal networks. This neurobiological model can explain additional aspects of agrammatics' performance.
Recognition of CVC Syllables from LVF, RVF, and Central Locations: Hemispheric Differences and Interhemispheric Interaction
Authors: Hellige Joseph B. , Cowin Elizabeth L. , Eng Tami L. 
Published: February 2008

Abstract
In each of two experiments, subjects were required to identify consonant-vowel-consonant nonsense syllables projected to the left visual fiel/right hemisphere (LVF/RH), right visual field/left hemisphere (RVF/LH), or to the CENTER of the visual field. There were fewer errors on RVF/LH than on LVF/RH trials and the pattern of errors was qualitatively different on RVF/LH and LVF/RH trials. The pattern of errors was consistent with the hypothesis that attention is distributed across the three letters in a relatively slow serial fashion on LVF/RH trials whereas attention is distributed more rapidly and evenly across the three letters on RVF/LH trials. Despite the large RVF/LH advantage, the qualitative pattern of errors on CENTER trials (when viewing conditions do not favor one hemisphere or the other) was very similar to the pattern obtained on LW/RH trials. Implications of this counterintuitive finding are considered for the nature of interhemispheric interaction.
Double Dissociation between Overt and Covert Face Recognition
Authors: Tranel Daniel , Damasio Hanna , Damasio Antonio R. 
Published: February 2008

Abstract
Some patients with face agnosia (prosopagnosia) caused by occipitotemporal damage produce discriminatory covert responses to the familiar faces that they fail to identify overtly. For example, their average skin conductance responses (SCRs) to familiar faces are significantly larger than average SCRs to unfamiliar faces. In this study we describe the opposite dissociation in four patients with bilateral ventromedial frontal damage: The patients recognized the identity of familiar faces normally, yet failed to generate discriminatory SCRs to those same familiar faces. Taken together, the two sets of results constitute a double dissociation: bilateral occipitotemporal damage impairs recognition but allows SCR discrimination, whereas bilateral ventromedial damage causes the opposite. The findings suggest that the neural systems that process the somatic-based valence of stimuli are separate from and parallel to the neural systems that process the factual, nonsomatic information associated with the same stimuli.
A Positron Emission Tomography Study of Visual and Mental Spatial Exploration
Authors: Mellet E. , Tzourio N. , Denis M. , Mazoyer B. 
Published: February 2008

Abstract
We measured normalized regional cerebral blood flow (NrCBF) using positron emission tomography (PET) and oxygen-15-labeled water in eight young right-handed healthy volunteers selected as high-imagers. during 2 runs of 3 different conditions: 1, rest in total darkness 2; visual exploration of a map 3; mental exploration of the same map in total darkness. NrCBF images were aligned with individual magnetic resonance images (MRI), and NrCBF variations between pairs of measurements (N = 15) were computed in regions of interest having anatomical boundaries that were defined using a three-dimensional (3-D) reconstruction of each subject MRI. During visual exploration, we found bilateral activations of primary visual areas, superior and inferior occipital gyri, fusiform and lingual gyri, cuneus and precuneus, bilateral superior parietal, and angular gyri. The right lateral premotor area was also activated during this task while superior temporal gyri and Broca's area were deactivated. By contrast, mental exploration activated the right superior occipital cortex, the supplementary motor area, and the cerebellar vermis. No activation was observed in the primary visual area. These results argue for a specific participation of the superior occipital cortex in the generation and maintenance of visual mental images.
Rapid Changes of Optical Parameters in the Human Brain During a Tapping Task
Authors: Gratton Gabriele , Fabiani Monica , Friedman David , Franceschini Maria Angela , Fantini Sergio , Corballis Paul , Gratton Enrico 
Published: February 2008

Abstract
Measures of parameters of the migration of near-infrared photons through the head (attenuation, or intensity, and time-of-flight, or delay) have been proposed as a way of assessing noninvasively and in a quasicontinuous fashion changes in the scattering and absorption properties of brain tissue. These, in turn, may reflect functional changes associated with behavioral tasks. To test this hypothesis, we measured changes of photon migration parameters from scalp locations proximal to the motor cortex from four human subjects, tapping at a rate of 0.8 Hz with their left or right hand, or with their left or right foot. Tapping produced both slow effects (requiring several seconds) and fast effects (tracking the tapping frequency). Slow effects were characterized by increase and delay of the light passing through the hemisphere contralateral to the tapping hand. Fast effects consisted of changes in the light delay during hand tapping. Monte Carlo simulations based on layer models of the brain indicated that fast effects are consistent with changes in deep layers of the head (presumably in the cortex), and that slow effects are consistent with either a shift of absorbing material toward deeper layers or a reduction in scattering. These results suggest that optical parameters can monitor rapid changes of brain activity, matching the contralateral organization of the motor cortex.
Neural Representations: Some Old Problems Revisited
Authors: Milner Peter M. 
Published: February 2008

Abstract
Hebb's (1949) cell assembly, originally conceived as an explanation for stimulus equivalence, also serves as a neural representation of stimuli. Association between cell assemblies was a major theme of Hebb's book, but the state of physiological knowledge at the time was such that no satisfactory basis for it could he devised. Subsequent theory has been more concerned with the recognition and “attractor” features of the cell assembly than its capacity to represent and associate concepts. This is unfortunate because while generalization is important, so is discrimination, which is not well served by an attractor model. This dilemma is avoided by postulating that stimulus representation and stimulus equivalence involve different neural circuits. Human beings can instantly form and use associations between many more concepts than there are synapses on the average cortical neuron, indicating that the associative links between engrams are sparse. The connections within an engram, on the other hand. must be dense to ensure that a weak input can activate all its neurons. It would appear that two processes are anatomically and physiologically different, which may account for the fact that engrams remain distinct in spite of being associated with each other. The fact that a single concept may have very many associations puts a heavy demand on the process of selective attention to avert complete chaos. I propose that attention is a manifestation of motivation. Motivation facilitates responses, which in turn facilitate engrams of associated stimuli. The enhanced engram activity is fed back through centrifugal paths to intensify sensory input that has previously played a part in executing the planned responses. Attention may also contribute to a mechanism that prevents the engrams of component parts of an object from being assimilated into the engram of the whole.
Development of Schemata during Event Parsing: Neisser's Perceptual Cycle as a Recurrent Connectionist Network
Authors: Hanson Catherine , Hanson Stephen José 
Published: February 2008

Abstract
Neural net simulations of human event parsing are described. A recurrent net was used to simulate data collected from human subjects watching short videotaped event sequences. In one simulation, the net was trained on one-half of a taped sequence with the other half of the sequence being used to test transfer performance. In another simulation, the net was trained on one complete event sequence and transfer to a different event sequence was tested. Neural net simulations provide a unique means of observing the interrelation of top-down and bottom-up processing in a basic cognitive task. Examination of computational patterns of the net and cluster analysis of the hidden units revealed two factors that may be central to event perception: (1) similarity between a current input and an activated schema and (2) expected duration of a given event. Although the importance of similarity between input and activated schemata during event perception has been acknowledged previously (e.g., Neisser, 1976; Schank, 1982), the present study provides specific instantiation of how similarity judgments can be made using both top-down and bottom-up processing. Moreover, unlike other work on event perception, this approach provides a potential mechanism for how schemata develop.
Progressive Nonfluent Aphasia: Language, Cognitive, and PET Measures Contrasted with Probable Alzheimer's Disease
Authors: Grossman Murray , Mickanin Jenifer , Onishi Kris , Hughes Elizabeth , D'Esposito Mark , Ding Xin-Sheng , Alavi Abass , Reivich Martin 
Published: February 2008

Abstract
The purpose of this study was to compare the language and cognitive profiles of four progressive nonfluent aphasia (PNFA) patients with 25 probable Alzheimer's disease (pAD) patients, and to identify the distinct cortical defects associated with cognitive deficits in PNFA using positron emission tomography (PET). Longitudinal observations of PNFA patients revealed progressively telegraphic speech and writing and a gradual deterioration of sentence comprehension, but memory and visual functioning were relatively preserved. Direct contrast with PAD patients revealed that PNFA patients are significantly impaired on grammatical phrase structure aspects of sentence comprehension and expression, phonemic judgments, repetition, and digit span, but not on other cognitive measures. PET studies of PNFA revealed reduced cortical activity throughout the left hemisphere. In addition, there was a prominent defect in left superior and middle temporal and inferior frontal regions of PNFA patients that differed significantly from the distribution of regional cerebral dysfunction in pAD. We conclude that PNFA is associated with a distinct profile of language and cognitive difficulty, and that this pattern of impairment is related to cortical dysfunction in a specific distribution of the left hemisphere.
The Search for “Common Sense”: An Electrophysiological Study of the Comprehension of Words and Pictures in Reading
Authors: Ganis Giorgio , Kutas Marta , Sereno Martin I. 
Published: February 2008

Abstract
Event-related brain potentials (ERPs) from 26 scalp sites were used to investigate whether or not and, if so, the extent to which the brain processes subserving the understanding of imageable written words and line drawings are identical. Sentences were presented one word at a time to 28 undergraduates for comprehension. Each sentence ended with either a written word (regular sentences) or with a line drawing (rebus sentences) that rendered it semantically congruous or semantically incongruous. For half of the subjects regular and rebus sentences were randomly intermixed whereas for the remaining half the regular and rebus sentences were presented in separate blocks (affording within-subject comparisons in both cases). In both presentation formats, words and line drawings generated greater negativity between 325 and 475 msec post-stimulus in ERPs to incongruous relative to congruous sentence endings (i.e., an N400-like effect). While the time course of this negativity was remarkably similar for words and pictures, there were notable differences in their scalp distributions; specifically, the classic N400 effect for words was larger posteriorly than it was for pictures. The congruity effect for pictures but not for words was also associated with a longer duration (lower frequency) negativity over frontal sites. In addition, under the mixed presentation mode, the N400 effect peaked about 30 msec earlier for pictures than for words. All in all, the data suggest that written words and pictures when they terminate sentences are processed similarly, but by at least partially nonoverlapping brain areas.
Dual Population Coding in the Neocortex: A Model of Interaction between Representation and Attention in the Visual Cortex
Authors: Koechlin Etienne , Burnod Yves 
Published: February 2008

Abstract
The text describes a model that extends the population coding principles to any multidimensional attribute. The model distinguishes between the distribution of cell activity and the overall activity of a population. The distribution of cell activity is assumed to encode attribute information, while overall activity is assumed to reflect the significance or pertinence of the encoded attribute in the cerebral cortex, according to the dual coding principle. Three basic mechanisms of interaction between the representation of attribute and pertinence are defined and are applied to the motion (MT-MST) cortical pathway in the visual cortex. This framework determines three sources of pertinence that model cognitive processing, including preattentive processing, spatial-selective attention, and object-selective attention. The model accommodates most of the published psychophysical, neurophysiological, and neuroanatomical data and makes several testable predictions about the representations of attribute and enhanced effects in these areas.
Implicit and Explicit Conceptual Memory Following Frontal Lobe Damage
Authors: Gershberg Felicia B. 
Published: February 2008

Abstract
In two experiments, the performance of patients with frontal lobe lesions was examined on implicit and explicit tests of conceptual memory for organized lists of words. Frontal patients exhibited normal levels of conceptual priming on implicit category production and free association tests, but they exhibited impaired memory performance on explicit category- and associate-cued recall tests. The findings of normal performance on implicit conceptual tests suggest that frontal patients do not have a basic deficit in semantic processing of individual items. Impaired performance on explicit cued recall tests may be related to deficits in the use of organizational encoding and strategic retrieval processes.
The End of the Line for a Brain-Damaged Model of Unilateral Neglect
Authors: Mozer Michael C. , Halligan Peter W. , Marshall John C. 
Published: February 2008

Abstract
For more than a century, it has been known that damage to the right hemisphere of the brain can cause patients to be unaware of the contralesional side of space. This condition, known as unilateral neglect, represents a collection of clinically related spatial disorders characterized by the failure in free vision to respond, explore, or orient to stimuli predominantly located on the side of space opposite the damaged hemisphere. Recent studies using the simple task of line bisection, a conventional diagnostic test, have proven surprisingly revealing with respect to the spatial and attentional impairments involved in neglect. In line bisection, the patient is asked to mark the midpoint of a thin horizontal lie on a sheet of paper. Neglect patients generally transect far to the right of the center. Extensive studies of line bisection have been conducted, manipulating-among other factors-line length, orientation, and position. We have simulated the pattern of results using an existing computational model of visual perception and selective attention called MORSEL (Mozer, 1991). MORSEL has already been used to model data in a related disorder, neglect dyslexia (Mozer & Behrmann, 1990). In this earlier work, MORSEL was “lesioned” in accordance with the damage we suppose to have occurred in the brains of neglect patients. The same model and lesion can simulate the detailed pattern of performance on line bisection, including the following observations: (1) no consistent across-subject bias is found in normals; (2) transection displacements are proportional to line length in neglect patients; (3) variability of displacements is proportional to line length, in both normals and patients; (4) position of the lines with respect to the body or the page on which they are drawn has little effect; and (5) for lines drawn at different orientations, displacements are proportional to the cosine of the orientation angle. MORSEL fails to account for one observation: across patients, the variability of displacements for a particular line length is roughly proportional to mean displacement. Nonetheless, the overall fit of the model is sufficiently good that we believe MORSEL can be used as a diagnostic tool to characterize the specific nature of a patient's deficit, and thereby has potential down the line in therapy.
Islands of Residual Vision in Hemianopic Patients
Authors: Wessinger C. Mark , Fendrich Robert , Gazzaniga Michael S. 
Published: February 2008

Abstract
Following damage to primary visual cortex, some patients our initial findings. The data reveal a patchy distribution of redemonstrate a limited ability to respond to stimuli they do not sidual visual abilities in the absence of acknowledged awareness. acknowledge seeing. This residual vision, which has been referred to as “blindsight,” has been attributed to secondary visual pathways. We previously reported an isolated island of blindsight in one patient and argued it was a likely consequence of cortical sparing in V1. We now report an extension of our initial findings. The data reveal a patchy distribution of residual visual abilities in the absence of acknowledged awareness. Variable patterns of cortical sparing appear to be the most parsimonious way to account for this outcome, suggesting that blindsight is generally mediated by the primary visual pathway.