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Abstract
While it is now well accepted that the brain reorganizes following sensory loss, the
neural mechanisms that give rise to this plasticity are not well understood. Anatomical
tract tracing studies have begun to shed light on the structural underpinnings of
cross-modal reorganization by comparing cerebral connectivity in sensory-deprived
animals to that of their non-deprived counterparts. However, so far, full documentation
of connectional patterns within hearing, congenitally deaf, as well as animals deafened
early versus later in life exist only for primary auditory cortex, a region not known
to undergo cross-modal reorganization in the deaf. The purpose of the present investigation
was to examine thalamo-cortical patterns of connectivity in hearing, late- and early-deafened
cats to the dorsal zone (DZ), a region of auditory cortex that cross-modally reorganizes
to mediate enhanced visual motion perception following deafness. In hearing cats,
the largest projections to DZ arose from the dorsal division of the medial geniculate
body (MGB) with lesser projections originating in the medial and ventral MGB and from
the suprageniculate and the lateral posterior nuclei. In general, while some variations
in the strength of specific thalamic projections were noted, the pattern of projections
arising from the thalamus in early- and late-deafened animals remained consistent
with that of hearing subjects. These results complement the existing thalamic connectivity
data described for congenitally deaf animals, which together demonstrate that thalamo-cortical
connectivity patterns to DZ are conserved following deafness, irrespective of the
time of onset and etiology of deafness.