Tonotopic organization in the avian telencephalon

Abstract

The mammalian and avian auditory pathways have distinctly homologous cell groupings. Tonotopic organization has been demonstrated by means of single unit recordings in the cochlear nuclei of both birds and mammals. The avian thalamic nucleus ovoidalis, the homolog of the mammalian medial geniculate body, has a discrete projection to an area of the telencephalic neostriatum caudale, field L (see ref. 6, 17). Although the primary projection of the ascending auditory pathway to the telencephalon of mammals has been shown to have a tonotopic organization, single unit recordings from neither field L of the ring dove nor that of the starling have produced evidence for a tonotopic organization of individual neurons of the avian telencephalon. The absence of tonotopic organization in field L of birds would appear to underscore the dissimilarities between the gross characteristics of field Land primary auditory cortex. We wish to report, however, an initial set of experiments using single unit recordings in a song bird, the zebra finch, which define a point-by-point projection from the avian cochlea to the auditory area of the telencephalon, the first such demonstration in a sensory pathway of an infra-mammalian vertebrate.