There is a large body of evidence, from psychophysics to brain imaging studies, that have shown in deaf human a functional reorganization that affects the remaining sensory modalities. Here, in a congenital deaf cat (CDC), we search for the possibility that the thalamo-cortical pathway could be the origin of such a cross-modal reorganization in the auditory system. Pairs of retrograde dyes injections were performed in the primary auditory cortex of CDC and normal hearing animals (NHC).
Preliminary results in the CDC showed that the main inputs (over 80%) to the primary auditory cortex originate from auditory nuclei of the ventral, dorsal and median division of the median geniculate body of thalamus (MGB) and from PO. The topographical organization of projection was similar to that observed in NHC with respect to the tonotopy of the MGB. We only found in CDC a sparse projection arising from the lateral posterior nuclei of thalamus (LP) that could relay non-auditory information to A1. These preliminary findings suggest that the cortical crossmodal reorganization observed in human subjects suffering of deafness, is probably mediated by a network outside the thalamo-cortical pathway.
Grant support: ANR-06-NEUR-021-01. BQR ATUPS 2007 Université Paul Sabatier.