Projections of the medial geniculate nucleus to layer 1 of the auditory cortex in the cat traced with horseradish peroxidase.

Thalamic afferents to layer 1 of the auditory cortex in the cat have been studied using retrograde axonal transport of horseradish peroxidase. The magnocellular part of the medial geniculate nucleus sends fibers to layer 1 of the primary and secondary auditory areas and of the dorsal division of the posterior ectosylvian area. The dorsal principal part and the ventromedial portion of the ventral principal part send only a few fibers to layer 1 of these cortical areas.