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192 Brain imaging studies of callosal transmission
Abstracts
/International
Journal
spheric pathways. Callosal pathology should thus affect interhemispheric comparisons and integration to a less extent. In agreement with this, the subjects who showed tactile deficits on the trunk had no difficulties comparing bilateral thermal stimulations, even at midline. The auditory system also has many cross-over points. Recordings of CC projection neurons do not show a bias for hearing at midline (as deduced from their sensitivity to interaural intensity and time disparities). Similarly, callosal recipient neurons do not show this preference and their relative proportion analyzing midline vs lateral positions is unchanged following CC transection. This lack of midline bias is confirmed behaviorally with the above patients, who localize sounds with a slight deficit but independently of its position on the sound perimeter. We have, however, shown that the direction of a simulated moving sound presented on the sagittal plane, hence using spectral cues for discrimination, is less well perceived by the acallosal subjects than by normals. In conclusion, the midline rule does apply, but not in all cases.
191 LATERALIZATION OF TASTE PERCEPTION CALLOSOTOMY PATIENT
IN A
G. Berlucchi’*, G. Tassinari’, S. Aglioti’, M.C. Corballis’ ‘Dip. Scienze Neurologiche e della Visione, Universita di Verona, Strada Le Grazie 8, Verona 37134, Italy *Department of Psychology, University of Auckland, New Zealand
A patient with a complete section of the corpus callosum and a right prefrontal lesion was tested for discrimination of sapid stimuli applied to the right or left sides of the tongue. The basic taste stimuli (bitter, salty, sour and sweet) were used, but most tests were run with acid and salt stimuli. Responses were made either by naming the stimulus or by pointing with either hand to written words corresponding to the stimuli. Accuracy and speed of performance were good when stimuli were applied to the left hemitongue, whereas the patient performed virtually at chance and with overlong response times when stimuli were applied to the right hemitongue. This right-left difference occurred independent of the type of response. The results are consistent with the hypothesis that the organization of the gustatory pathways is strictly uncrossed, the taste receptors in each hemitongue projecting to the ipsilateral hemisphere, and that the corpus callosum is necessary for interhemispheric transfer of taste information. Considering that in this patient language is normally lateralized to the left hemisphere, the disconnected right hemisphere may have had difficulties in performing the task either because responses were based on language, or because the right prefrontal lesion may partially encroach upon cortical gustatory areas, or because of both reasons.
of Psychophysiology
30 (1998)
192 BRAIN IMAGING SMISSION
7-94
STUDIES OF CALLOSAL
15 TRAN-
C.A. Marzi’*, D. Perani’, G. Tassinari’, A. Colleluori3, A. Maravita’, C. Miniussi’, E. Paulesu3, F. Fazio2,3,4 ‘Dept. of Neurological and Visual Sci., Univ. of Verona, Strada Le Grazie, Verona 37134, Italy *Institute of Neuroscience and Bioimaging C.N.R., Milan, Italy 31RCCS H San Raffaele, Milan, Italy 4Dept. Nuclear Medicine, University of Milan, Milan, Italy We studied with PET the intra- and interhemispheric pathways subserving a simple speeded visuomotor task. Six normal subjects and one patient with a complete section of the corpus callosum (M.E.) had their rCBF measured with PET under conditions of lateralized tachistoscopic visual presentations in a manual simple reaction time (RT) paradigm. Confirming previous behavioural findings, we found that on average crossed hand/hemifield conditions, i.e. those requiring an interhemispheric transfer, yielded a longer RT than uncrossed conditions and that this difference was markedly larger in the split-brain subject. In normal subjects, the Brodmann areas (BA) specifically activated in the uncrossed conditions (47,45, 31, 8,) were anterior to the VCA plane (verticofrontal plane passing through the anterior commissure) whereas activation foci posterior to this plane were activated only in the crossed conditions (BA 7, 19,391. These results suggest that visuo-motor interhemispheric transfer takes place through the widespread callosal fibres interconnecting the parietal cortices of the two hemispheres. The pattern of activation in the two transfer conditions was markedly different in M.E. and this reflects the subcortical nature of interhemispheric transfer in this subject and possibly the contributions of the intact anterior commissure.
193 ELECfROPHYSIOLOGICAL EVIDENCE FOR INTERHEMISPHERIC INTERACTION IN CALLOSAL AGENESIS M. Lassonde’, C.D. Saron2, H.G. Vaughan, Jr.*, J.J. Foxe283, S.P. A&hors2 and G.V. Simpson2 ‘Universite de Montreal, Montreal, USA *Albert Einstein College of Medicine and Iona College The corpus callosum is the major interhemispheric pathway in neurologically normal adults. In individuals presenting a congenital absence of the corpus callosum, neuropsychological studies have focused on the absence of a disconnection syndrome and several have maintained that interhemispheric communication was performed via either the anterior or subcortical commissures in these subjects. The aim of the present
/International
Journal
spheric pathways. Callosal pathology should thus affect interhemispheric comparisons and integration to a less extent. In agreement with this, the subjects who showed tactile deficits on the trunk had no difficulties comparing bilateral thermal stimulations, even at midline. The auditory system also has many cross-over points. Recordings of CC projection neurons do not show a bias for hearing at midline (as deduced from their sensitivity to interaural intensity and time disparities). Similarly, callosal recipient neurons do not show this preference and their relative proportion analyzing midline vs lateral positions is unchanged following CC transection. This lack of midline bias is confirmed behaviorally with the above patients, who localize sounds with a slight deficit but independently of its position on the sound perimeter. We have, however, shown that the direction of a simulated moving sound presented on the sagittal plane, hence using spectral cues for discrimination, is less well perceived by the acallosal subjects than by normals. In conclusion, the midline rule does apply, but not in all cases.
191 LATERALIZATION OF TASTE PERCEPTION CALLOSOTOMY PATIENT
IN A
G. Berlucchi’*, G. Tassinari’, S. Aglioti’, M.C. Corballis’ ‘Dip. Scienze Neurologiche e della Visione, Universita di Verona, Strada Le Grazie 8, Verona 37134, Italy *Department of Psychology, University of Auckland, New Zealand
A patient with a complete section of the corpus callosum and a right prefrontal lesion was tested for discrimination of sapid stimuli applied to the right or left sides of the tongue. The basic taste stimuli (bitter, salty, sour and sweet) were used, but most tests were run with acid and salt stimuli. Responses were made either by naming the stimulus or by pointing with either hand to written words corresponding to the stimuli. Accuracy and speed of performance were good when stimuli were applied to the left hemitongue, whereas the patient performed virtually at chance and with overlong response times when stimuli were applied to the right hemitongue. This right-left difference occurred independent of the type of response. The results are consistent with the hypothesis that the organization of the gustatory pathways is strictly uncrossed, the taste receptors in each hemitongue projecting to the ipsilateral hemisphere, and that the corpus callosum is necessary for interhemispheric transfer of taste information. Considering that in this patient language is normally lateralized to the left hemisphere, the disconnected right hemisphere may have had difficulties in performing the task either because responses were based on language, or because the right prefrontal lesion may partially encroach upon cortical gustatory areas, or because of both reasons.
of Psychophysiology
30 (1998)
192 BRAIN IMAGING SMISSION
7-94
STUDIES OF CALLOSAL
15 TRAN-
C.A. Marzi’*, D. Perani’, G. Tassinari’, A. Colleluori3, A. Maravita’, C. Miniussi’, E. Paulesu3, F. Fazio2,3,4 ‘Dept. of Neurological and Visual Sci., Univ. of Verona, Strada Le Grazie, Verona 37134, Italy *Institute of Neuroscience and Bioimaging C.N.R., Milan, Italy 31RCCS H San Raffaele, Milan, Italy 4Dept. Nuclear Medicine, University of Milan, Milan, Italy We studied with PET the intra- and interhemispheric pathways subserving a simple speeded visuomotor task. Six normal subjects and one patient with a complete section of the corpus callosum (M.E.) had their rCBF measured with PET under conditions of lateralized tachistoscopic visual presentations in a manual simple reaction time (RT) paradigm. Confirming previous behavioural findings, we found that on average crossed hand/hemifield conditions, i.e. those requiring an interhemispheric transfer, yielded a longer RT than uncrossed conditions and that this difference was markedly larger in the split-brain subject. In normal subjects, the Brodmann areas (BA) specifically activated in the uncrossed conditions (47,45, 31, 8,) were anterior to the VCA plane (verticofrontal plane passing through the anterior commissure) whereas activation foci posterior to this plane were activated only in the crossed conditions (BA 7, 19,391. These results suggest that visuo-motor interhemispheric transfer takes place through the widespread callosal fibres interconnecting the parietal cortices of the two hemispheres. The pattern of activation in the two transfer conditions was markedly different in M.E. and this reflects the subcortical nature of interhemispheric transfer in this subject and possibly the contributions of the intact anterior commissure.
193 ELECfROPHYSIOLOGICAL EVIDENCE FOR INTERHEMISPHERIC INTERACTION IN CALLOSAL AGENESIS M. Lassonde’, C.D. Saron2, H.G. Vaughan, Jr.*, J.J. Foxe283, S.P. A&hors2 and G.V. Simpson2 ‘Universite de Montreal, Montreal, USA *Albert Einstein College of Medicine and Iona College The corpus callosum is the major interhemispheric pathway in neurologically normal adults. In individuals presenting a congenital absence of the corpus callosum, neuropsychological studies have focused on the absence of a disconnection syndrome and several have maintained that interhemispheric communication was performed via either the anterior or subcortical commissures in these subjects. The aim of the present