Organization of protection from the central nucleus of the inferior colliculus into the medial geniculate body of cat

Orthograde tracer experiments were conducted to define, in detail, projections of the central nucleus of the inferior colliculus (ICC) into the medial geniculate body (MGB). Injections of 3H-1-leucine were introduced at physiologically defined loci within the ICC. The bilateral and spacially symmetrical projection was less dense to the contralateral MGB. The projection into the MGB formed a medial column passing rostrocaudally through the medial and deep dorsal nuclei; and formed a more lateral sheet passing rostrocaudally within the ventral nucleus and continuous through the lateral, transitional, and ovoidal subdivisions of the nucleus. Projections were topographically ordered within all labeled subdivisions of MGB. Bands of periodic light and heavy labeling were often seen approximately normal to the morphological laminations of the lateral division of the ventral nucleus. The basic pattern and topographic (cochleotopic) organization of the ICC projection into the MGB was indistinguishable from the pattern and topographic (cochleotopic) organization of the thalamocortical and corticothalamic projections. [Supported by NIH grant NS-10414 and Hearing Research Inc.]