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Role and development of the corpus callosum for the interhemispheric transfer of visual motion

Periodic Report Summary 2 - DIRCALLOSDVPT (Role and development of the corpus callosum for the interhemispheric transfer of visual motion)

Our perception of the world is mainly dynamic. In order to interact adequately with the environment, our brain must analyse rapidly and efficiently various kinds of motion present in the visual world, including complex motions such as the optic flow induced by our own movements. The primary visual cortex, through its direction-selective cells, is the first cortical step toward such integration. Each hemifield is analysed by one hemisphere, and the corpus callosum is thought to link these two representations into a single dynamic scene. Using cat model and optical imaging technique, the DIRCALLOSDVPT project sought to elucidate the role of the corpus callosum in the interhemispheric transfer of visual motion.

Results show that transcallosal signals related to the direction of visual motion are organised and form maps: Neighbouring neurons are generally optimally activated through the corpus callosum by similar directions of motion, although fractures at which neighbouring neurons prefer opposite directions can also be observed. These transcallosal direction maps resemble those activated through the direct geniculo-cortical pathway and suggest that corpus callosum insures the continuity in the perceived visual motion between the two hemispheres. With the help of project partners, functional selectivity of inter-hemispheric connections is also studied by combining optical imaging with anatomical tracer injection. For this purpose, single transcallosal axons are reconstructed in 3D, and bouton terminals location is evaluated with respect to preferred direction of motion.

Involvement of corpus callosum in the perception of spatial frequency is also investigated in order to see how information about fine details of the visual scene is transferred from one hemisphere to the other. As for direction of motion, spatial frequency appears to be organised. A gradient from low to high spatial frequency preference can be observed parallel to the 17/18 border. Voltage-sensitive dye recording experiments moreover show that transcallosal signals carrying low and high spatial frequencies have different time course.
% L DIRCALLOSDVPT expects that the results of this project will offer new insights on how the two hemispheres communicate with each other at the level of the primary visual cortex.