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Articles 691 - 714 of 714

Full-Text Articles in Medical Sciences

Double Dissociation Between The Effects Of Peri-Postrhinal Cortex And Hippocampal Lesions On Tests Of Object Recognition And Spatial Memory: Heterogeneity Of Function Within The Temporal Lobe., Boyer D Winters, Suzanna E Forwood, Rosemary A Cowell, Lisa M Saksida, Timothy J Bussey Jun 2004

Double Dissociation Between The Effects Of Peri-Postrhinal Cortex And Hippocampal Lesions On Tests Of Object Recognition And Spatial Memory: Heterogeneity Of Function Within The Temporal Lobe., Boyer D Winters, Suzanna E Forwood, Rosemary A Cowell, Lisa M Saksida, Timothy J Bussey

Brain and Mind Institute Researchers' Publications

It is widely believed that declarative memory is mediated by a medial temporal lobe memory system consisting of several distinct structures, including the hippocampus and perirhinal cortex. The strong version of this view assumes a high degree of functional homogeneity and serial organization within the medial temporal lobe, such that double dissociations between individual structures should not be possible. In the present study, we tested for a functional double dissociation between the hippocampus and peri-postrhinal cortex in a single experiment. Rats with bilateral excitotoxic lesions of either the hippocampus or peri-postrhinal cortex were assessed in tests of spatial memory (radial …

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Somatotopic Representation Of Action Words In Human Motor And Premotor Cortex, Olaf Hauk, Ingrid Johnsrude, Friedemann Pulvermüller Jan 2004

Somatotopic Representation Of Action Words In Human Motor And Premotor Cortex, Olaf Hauk, Ingrid Johnsrude, Friedemann Pulvermüller

Brain and Mind Institute Researchers' Publications

Since the early days of research into language and the brain, word meaning was assumed to be processed in specific brain regions, which most modern neuroscientists localize to the left temporal lobe. Here we use event-related fMRI to show that action words referring to face, arm, or leg actions (e.g., to lick, pick, or kick), when presented in a passive reading task, differentially activated areas along the motor strip that either were directly adjacent to or overlapped with areas activated by actual movement of the tongue, fingers, or feet. These results demonstrate that the referential meaning of action words has …

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Gaze-Centered Updating Of Visual Space In Human Parietal Cortex., W Pieter Medendorp, Herbert C Goltz, Tutis Vilis, J Douglas Crawford Jul 2003

Gaze-Centered Updating Of Visual Space In Human Parietal Cortex., W Pieter Medendorp, Herbert C Goltz, Tutis Vilis, J Douglas Crawford

Brain and Mind Institute Researchers' Publications

Single-unit recordings have identified a region in the posterior parietal cortex (PPC) of the monkey that represents and updates visual space in a gaze-centered frame. Here, using event-related functional magnetic resonance imaging, we identified an analogous bilateral region in the human PPC that shows contralateral topography for memory-guided eye movements and arm movements. Furthermore, when eye movements reversed the remembered horizontal target location relative to the gaze fixation point, this PPC region exchanged activity across the two cortical lobules. This shows that the human PPC dynamically updates the spatial goals for action in a gaze-centered frame.

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The Lateral Occipital Complex Subserves The Perceptual Persistence Of Motion-Defined Groupings., Susanne Ferber, G Keith Humphrey, Tutis Vilis Jul 2003

The Lateral Occipital Complex Subserves The Perceptual Persistence Of Motion-Defined Groupings., Susanne Ferber, G Keith Humphrey, Tutis Vilis

Brain and Mind Institute Researchers' Publications

How are the bits and pieces of retinal information assembled and integrated to form the coherent objects that we see? One long-established principle is that elements that move as a group are linked together. For instance a fragmented line-drawing of an object, placed on a background of randomly distributed short lines, can be impossible to see. But if the object moves relative to the background, its shape is instantly recognized. Even after the motion stops, the percept of the object persists briefly before it fades into the background of random lines. Where in the brain does the percept of the …

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Effects Of Ethanol On Anti-Saccade Task Performance., Sarah A Khan, Kristen Ford, Brian Timney, Stefan Everling May 2003

Effects Of Ethanol On Anti-Saccade Task Performance., Sarah A Khan, Kristen Ford, Brian Timney, Stefan Everling

Brain and Mind Institute Researchers' Publications

It has been shown that saccade-related neurons in the superior colliculus (SC) display an increased level of prestimulus activity and a higher stimulus-related burst in action potentials preceding direction errors in the anti-saccade task compared with correct anti-saccades. From this, it has been hypothesized that errors occur when the incoming visual signal in the SC passes a threshold and triggers a reflexive saccade. This hypothesis predicts that an attenuated visual signal will reduce the number of direction errors. Since ethanol has been shown to have a suppressive effect on cortical visual event-related potentials (ERPs), the purpose of the present study …

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Hierarchical Processing In Spoken Language Comprehension., Matthew H Davis, Ingrid Johnsrude Apr 2003

Hierarchical Processing In Spoken Language Comprehension., Matthew H Davis, Ingrid Johnsrude

Brain and Mind Institute Researchers' Publications

Understanding spoken language requires a complex series of processing stages to translate speech sounds into meaning. In this study, we use functional magnetic resonance imaging to explore the brain regions that are involved in spoken language comprehension, fractionating this system into sound-based and more abstract higher-level processes. We distorted English sentences in three acoustically different ways, applying each distortion to varying degrees to produce a range of intelligibility (quantified as the number of words that could be reported) and collected whole-brain echo-planar imaging data from 12 listeners using sparse imaging. The blood oxygenation level-dependent signal correlated with intelligibility along the …

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Relationships Between Human Auditory Cortical Structure And Function, Deborah A Hall, Heledd C Hart, Ingrid Johnsrude Jan 2003

Relationships Between Human Auditory Cortical Structure And Function, Deborah A Hall, Heledd C Hart, Ingrid Johnsrude

Brain and Mind Institute Researchers' Publications

The human auditory cortex comprises multiple areas, largely distributed across the supratemporal plane, but the precise number and configuration of auditory areas and their functional significance have not yet been clearly established. In this paper, we discuss recent research concerning architectonic and functional organisation within the human auditory cortex, as well as architectonic and neurophysiological studies in non-human species, which can provide a broad conceptual framework for interpreting functional specialisation in humans. We review the pattern in human auditory cortex of the functional responses to various acoustic cues, such as frequency, pitch, sound level, temporal variation, motion and spatial location, …

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Spectral And Temporal Processing In Human Auditory Cortex, Deborah A Hall, Ingrid Johnsrude, Mark P Haggard, Alan R Palmer, Michael A Akeroyd, A Quentin Summerfield Feb 2002

Spectral And Temporal Processing In Human Auditory Cortex, Deborah A Hall, Ingrid Johnsrude, Mark P Haggard, Alan R Palmer, Michael A Akeroyd, A Quentin Summerfield

Brain and Mind Institute Researchers' Publications

Hierarchical processing suggests that spectrally and temporally complex stimuli will evoke more activation than do simple stimuli, particularly in non-primary auditory fields. This hypothesis was tested using two tones, a single frequency tone and a harmonic tone, that were either static or frequency modulated to create four stimuli. We interpret the location of differences in activation by drawing comparisons between fMRI and human cytoarchitectonic data, reported in the same brain space. Harmonic tones produced more activation than single tones in right Heschl's gyrus (HG) and bilaterally in the lateral supratemporal plane (STP). Activation was also greater to frequency-modulated tones than …

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Can Meaningful Effective Connectivities Be Obtained Between Auditory Cortical Regions?, M S Gonçalves, D A Hall, Ingrid Johnsrude, M P Haggard Dec 2001

Can Meaningful Effective Connectivities Be Obtained Between Auditory Cortical Regions?, M S Gonçalves, D A Hall, Ingrid Johnsrude, M P Haggard

Brain and Mind Institute Researchers' Publications

Structural equation modeling (SEM) of neuroimaging data can be evaluated both for the goodness of fit of the model and for the strength of path coefficients (as an index of effective connectivity). SEM of auditory fMRI data is made difficult by the necessary sparse temporal sampling of the time series (to avoid contamination of auditory activation by the response to scanner noise) and by the paucity of well-defined anatomical information to constrain the functional model. We used SEM (i.e., a model incorporating latent variables) to investigate how well fMRI data in four adjacent cortical fields can be described as an …

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Discrimination Of Computer-Graphic Stimuli By Mice: A Method For The Behavioral Characterization Of Transgenic And Gene-Knockout Models., T J Bussey, L M Saksida, L A Rothblat Aug 2001

Discrimination Of Computer-Graphic Stimuli By Mice: A Method For The Behavioral Characterization Of Transgenic And Gene-Knockout Models., T J Bussey, L M Saksida, L A Rothblat

Brain and Mind Institute Researchers' Publications

An automated method is described for the behavioral testing of mice in an apparatus that allows computer-graphic stimulus material to be presented. Mice responded to these stimuli by making a nose-poke toward a computer monitor that was equipped with a touchscreen attachment for detecting responses. It was found that C57BL/6 mice were able to solve single-pair visual discriminations as well as 3-pair concurrent visual discriminations. The finding that mice are capable of complex visual discriminations introduces the possibility of testing mice on nonspatial tasks that are similar to those used with rats, monkeys, and humans. Furthermore, the method seems particularly …

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Eye Position Sense Contributes To The Judgement Of Slant., F M James, S Whitehead, G K Humphrey, M S Banks, T Vilis Jan 2001

Eye Position Sense Contributes To The Judgement Of Slant., F M James, S Whitehead, G K Humphrey, M S Banks, T Vilis

Brain and Mind Institute Researchers' Publications

We measured monocular judgements of the slant of a cube face while varying eye position in the absence of stereoscopic and external lighting cues. Errors were found to be small, only 10% on average of the cube's eccentricity. Two factors appear to have contributed approximately equally to this error: an underestimate of cube slant as seen by the eye and an underestimate of eye position. When prism adaptation altered the sensed eye position, the pattern of slant judgements changed to reflect the altered sense of eye position.

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Eye Position Signal Modulates A Human Parietal Pointing Region During Memory-Guided Movements., J F Desouza, S P Dukelow, J S Gati, R S Menon, R A Andersen, T Vilis Aug 2000

Eye Position Signal Modulates A Human Parietal Pointing Region During Memory-Guided Movements., J F Desouza, S P Dukelow, J S Gati, R S Menon, R A Andersen, T Vilis

Brain and Mind Institute Researchers' Publications

Using functional magnetic resonance imaging, we examined the signal in parietal regions that were selectively activated during delayed pointing to flashed visual targets and determined whether this signal was dependent on the fixation position of the eyes. Delayed pointing activated a bilateral parietal area in the intraparietal sulcus (rIPS), rostral/anterior to areas activated by saccades. During right-hand pointing to centrally located targets, the left rIPS region showed a significant increase in activation when the eye position was rightward compared with leftward. As expected, activation in motor cortex showed no modulation when only eye position changed. During pointing to retinotopically identical …

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Navigation-Related Structural Change In The Hippocampi Of Taxi Drivers, E A Maguire, D G Gadian, Ingrid Johnsrude, C D Good, J Ashburner, R S Frackowiak, C D Frith Apr 2000

Navigation-Related Structural Change In The Hippocampi Of Taxi Drivers, E A Maguire, D G Gadian, Ingrid Johnsrude, C D Good, J Ashburner, R S Frackowiak, C D Frith

Brain and Mind Institute Researchers' Publications

Structural MRIs of the brains of humans with extensive navigation experience, licensed London taxi drivers, were analyzed and compared with those of control subjects who did not drive taxis. The posterior hippocampi of taxi drivers were significantly larger relative to those of control subjects. A more anterior hippocampal region was larger in control subjects than in taxi drivers. Hippocampal volume correlated with the amount of time spent as a taxi driver (positively in the posterior and negatively in the anterior hippocampus). These data are in accordance with the idea that the posterior hippocampus stores a spatial representation of the environment …

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Local And Global Stereopsis In The Horse., B Timney, K Keil May 1999

Local And Global Stereopsis In The Horse., B Timney, K Keil

Brain and Mind Institute Researchers' Publications

Although horses have laterally-placed eyes, there is substantial binocular overlap, allowing for the possibility that these animals have stereopsis. In the first experiment of the present study we measured local stereopsis by obtaining monocular and binocular depth thresholds for renal depth stimuli. On all measures, the horses' binocular performance was superior to their monocular. When depth thresholds were obtained, binocular thresholds were several times superior to those obtained monocularly, suggesting that the animals could use stereoscopic information when it was available. The binocular thresholds averaged about 15 min arc. In the second experiment we obtained evidence for the presence of …

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Perceptual-Mnemonic Functions Of The Perirhinal Cortex., Murray, Bussey Apr 1999

Perceptual-Mnemonic Functions Of The Perirhinal Cortex., Murray, Bussey

Brain and Mind Institute Researchers' Publications

It is widely acknowledged that the perirhinal cortex, located in the ventromedial aspect of the temporal lobe, is essential for certain types of memory in macaque monkeys. For example, removal of the perirhinal cortex yields severe impairments on tests of stimulus recognition and stimulus-stimulus association. There is considerable disagreement, however, about the most accurate way to characterize the function of the perirhinal cortex; some views emphasize a role in perception whereas others posit a role exclusively in declarative memory. In this article, we review recent findings from anatomical, physiological and ablation studies in monkeys, and discuss related findings obtained in …

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Uwomj Volume 69, No 2, Spring 1999, Western University Jan 1999

Uwomj Volume 69, No 2, Spring 1999, Western University

University of Western Ontario Medical Journal

An interdisciplinary medical science publication; established 1930.

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Functionally Dissociating Aspects Of Event Memory: The Effects Of Combined Perirhinal And Postrhinal Cortex Lesions On Object And Place Memory In The Rat., T J Bussey, J L Muir, J P Aggleton Jan 1999

Functionally Dissociating Aspects Of Event Memory: The Effects Of Combined Perirhinal And Postrhinal Cortex Lesions On Object And Place Memory In The Rat., T J Bussey, J L Muir, J P Aggleton

Brain and Mind Institute Researchers' Publications

Reciprocal interactions between the hippocampus and the perirhinal and parahippocampal cortices form core components of a proposed temporal lobe memory system. For this reason, the involvement of the hippocampus in event memory is thought to depend on its connections with these cortical areas. Contrary to these predictions, we found that NMDA-induced lesions of the putative rat homologs of these cortical areas (perirhinal plus postrhinal cortices) did not impair performance on two allocentric spatial tasks highly sensitive to hippocampal dysfunction. Remarkably, for one of the tasks there was evidence of a facilitation of performance. The same cortical lesions did, however, disrupt …

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Fornix Lesions Can Facilitate Acquisition Of The Transverse Patterning Task: A Challenge For "Configural" Theories Of Hippocampal Function., T J Bussey, E Clea Warburton, J P Aggleton, J L Muir Feb 1998

Fornix Lesions Can Facilitate Acquisition Of The Transverse Patterning Task: A Challenge For "Configural" Theories Of Hippocampal Function., T J Bussey, E Clea Warburton, J P Aggleton, J L Muir

Brain and Mind Institute Researchers' Publications

Configural theories of hippocampal function predict that hippocampal dysfunction should impair acquisition of the transverse patterning task, which involves the concurrent solution of three discrimination problems: A+ versus B-; B+ versus C-; and C+ versus A-. The present study tested this prediction in rats using computer-graphic stimuli presented on a touchscreen. Experiment 1 assessed the effects of fornix lesions when the three problems were introduced sequentially (phase 1: A+ vs B-; phase 2: A+ vs B-, B+ vs C-; phase 3: A+ vs B-, B+ vs C-, C+ vs A-). Fornix lesions significantly facilitated acquisition of the complete transverse patterning …

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Identifying Global Anatomical Differences: Deformation-Based Morphometry, J Ashburner, C Hutton, R Frackowiak, Ingrid Johnsrude, C Price, K Friston Jan 1998

Identifying Global Anatomical Differences: Deformation-Based Morphometry, J Ashburner, C Hutton, R Frackowiak, Ingrid Johnsrude, C Price, K Friston

Brain and Mind Institute Researchers' Publications

The aim of this paper is to illustrate a method for identifying macroscopic anatomical differences among the brains of different populations of subjects. The method involves spatially normalizing the structural MR images of a number of subjects so that they all conform to the same stereotactic space. Multivariate statistics are then applied to the parameters describing the estimated nonlinear deformations that ensue. To illustrate the method, we compared the gross morphometry of male and female subjects. We also assessed brain asymmetry, the effect of handedness, and interactions among these effects.

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Right Medial Temporal-Lobe Contribution To Object-Location Memory, B Milner, Ingrid Johnsrude, J Crane Oct 1997

Right Medial Temporal-Lobe Contribution To Object-Location Memory, B Milner, Ingrid Johnsrude, J Crane

Brain and Mind Institute Researchers' Publications

An important aspect of normal human memory, and one humans share with many other species, is the ability to remember the location of objects in their environment. There is by now strong evidence from the study of epileptic patients undergoing brain surgery that right temporal-lobe lesions that encroach extensively upon the hippocampal and parahippocampal gyrus impair the delayed, but not the immediate, recall of the location of objects within a random array. These findings have now been extended to a multiple-trial, spatial-array learning task; by including not only patients tested after unilateral anterior temporal lobectomy but also those with a …

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Triple Dissociation Of Anterior Cingulate, Posterior Cingulate, And Medial Frontal Cortices On Visual Discrimination Tasks Using A Touchscreen Testing Procedure For The Rat., T J Bussey, J L Muir, B J Everitt, T W Robbins Oct 1997

Triple Dissociation Of Anterior Cingulate, Posterior Cingulate, And Medial Frontal Cortices On Visual Discrimination Tasks Using A Touchscreen Testing Procedure For The Rat., T J Bussey, J L Muir, B J Everitt, T W Robbins

Brain and Mind Institute Researchers' Publications

Four experiments examined effects of quinolinic acid-induced lesions of the anterior cingulate, posterior cingulate, and medial frontal cortices on tests of visual discrimination learning, using a new "touchscreen" testing method for rats. Anterior cingulate cortex lesions impaired acquisition of an 8-pair concurrent discrimination task, whereas posterior cingulate cortex lesions facilitated learning but selectively impaired the late stages of acquisition of a visuospatial conditional discrimination. Medial frontal cortex lesions selectively impaired reversal learning when stimuli were difficult to discriminate; lesions of anterior and posterior cingulate cortex had no effect. These results suggest roles for the anterior cingulate, posterior cingulate, and medial …

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Uwomj Volume 66, No 2, Summer 1997, Western University Jan 1997

Uwomj Volume 66, No 2, Summer 1997, Western University

University of Western Ontario Medical Journal

An interdisciplinary medical science publication, established in 1930.

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Uwomj Volume 65, No 2, Spring 1996, Western University Jan 1996

Uwomj Volume 65, No 2, Spring 1996, Western University

University of Western Ontario Medical Journal

An interdisciplinary medical science publication, established in 1930.

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Uwomj Volume 65, No 1, Winter 1995-96, Western University Jan 1995

Uwomj Volume 65, No 1, Winter 1995-96, Western University

University of Western Ontario Medical Journal

An interdisciplinary medical science publication, established in 1930.

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