THE STRUCTURAL BASIS OF CORTICAL SYNCHRONIZATION. II. EFFECTS OF CORTICAL
LESIONS.
MUNK, M.H.J., NOWAK, L.G., NELSON, J.I., BULLIER J.
Cerveau et Vision, INSERM Unit[acute]e 371, 18 avenue du Doyen
L[acute]epine, 69500 Bron/Lyon France, t[acute]el: (33) 72 13 15 83, fax: (33)
72 13 15 99.
APStracts 2:0260N, 1995.
SUMMARY AND CONCLUSIONS
1. In order to understand the structural basis of the different types of
interhemispheric synchronizations described in the preceding paper, we made
sections of the corpus callosum and lesions of extrastriate cortex. We
measured the effects of such operations on the frequency of encounter, width
and strength of T, C and H peaks in cross-correlation histograms (CCHs)
computed from single and multi-unit recordings from areas 17-18 of opposite
cortical hemispheres in the cat. 2. Section of the corpus callosum led to a
complete abolition of T and C couplings and a strong reduction of encounter
rate and strength of H coupling. A section limited to the posterior half of
the corpus callosum abolished completely T and C couplings. This suggests that
T and C couplings are mediated by the direct reciprocal connections between
visual cortical areas circulating through the posterior part of the corpus
callosum. 3. The encounter rate of H peaks depended upon the extent of the
callosal cut. Larger lesions gave a more pronounced reduction of the number of
H peaks. From this observation we conclude that H peaks are, at least
partially, mediated by polysynaptic pathways involving widely distributed
cortical regions. 4. Extensive lesions of extrastriate cortex were made by
aspiration of the grey matter or injections of ibotenic acid. These lesions
removed the direct inputs from cortical areas sending ipsilateral as well as
contralateral inputs to the area 17-18 border region. Encounter rate and
coupling strength of C and H peaks were decreased whereas little effect was
observed on T peaks. 5. These results demonstrate that all types of
interhemispheric synchronization are mediated by corticocortical connections
and that T and C peaks are generated by reciprocal connections between areas
17/18 of each hemisphere. Feedback connections play a role in mediating or
facilitating the C and H types of interhemispheric synchronization.
Received 12 May 1995; accepted in final form 27 July 1995.
APS Manuscript Number J258-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 15 September 1995.