Differential neural projections to regions of the inferior colliculus of the cat responsive to high frequency sounds.

Iontophoretic injections of horseradish peroxidase were made in the vicinity of high best frequency neurons in the central nucleus of the inferior colliculus of the cat. Retrogradely labelled cells were found in most major auditory nuclei known to provide afferent input to the central nucleus, and were distributed in accordance with the known tonotopic organization of these nuclei. However, different injection sites gave rise to patterns of brain stem labelling that differed from one experiment to the next, in spite of the similarities in injection site best frequency. With each injection a small group of nuclei contained the majority of labelled cells. The results confirm previous anatomical findings of convergence of ascending input in relation to the tonotopic organization of the central nucleus. Additionally it is suggested that different subregions of the central nucleus may have different roles in the integration of acoustic information because of the varying patterns of brain stem terminations in each region.