Tonotopic and somatotopic representation in the nucleus basalis of the barn owl, Tyro alba

We have investigated the somatosensory and auditory representations in the nucleus basalis of the barn owl. In pigeons and finches, the nucleus basali s contains a representation of the beak and an auditory area. In the barn o wl, the nucleus basalis also contains a complete somatotopic map of the hea d and body (as in the budgerigar), with a tonotopically organized auditory area in close proximity to the representation of the facial ruff and the pr eaural area. Recordings within and around the nucleus basalis revealed pred ominantly (about 80%) contralateral responses to somatic stimulation. The s omatotopic map was oriented with the head down and rostral, Penetrations re vealed an over-representation of the feet in dorsal basalis, followed by th e rest of the body and wings more ventrally. Towards more rostral positions in nucleus basalis, responses from the head and beak predominated ventrall y. The auditory response area was encountered below the region that respond ed to stimulation of the facial ruff and preaural flap regions and above a region responsive to beak stimulation. Auditory responses were tonotopicall y organized, with low best frequencies dorsal. Some penetrations yielded pr edominantly monaural responses with a fairly broad dynamic range, similar t o those recorded from the ventral nucleus of the lateral lemniscus (LLV) an d the cochlear nucleus angularis, whereas other penetrations contained pred ominantly binaural responses sensitive to interaural time differences (ITD) . The physiological responses could be predicted on the basis of auditory p rojections to the nucleus basalis, An injection of biotinylated dextran ami ne (BDA) in the auditory region of nucleus basalis retrogradely labeled cel ls in both the caudal and rostral parts of the intermediate lateral lemnisc al nucleus (LLlc and LLlr), and a few cells in the anterior part of the dor sal lateral lemniscal nucleus (LLDa, previously known as nucleus ventralis lemnisci lateralis, pars anterior, or VLVa) and in the posterior part of th e dorsal lateral lemniscal nucleus (LLDp, previously known as nucleus ventr alis lemnisci lateralis, pars posterior, or VLVp). A large injection of cho lera toxin B-chain (CTB) into the nucleus basalis also produced dense retro grade labeling of a previously unidentified nucleus on the lateral aspect o f the rostral pens, that we here call nucleus pontis externus (PE). An inje ction of CTB into PE produced dense retrograde labeling of the contralatera l dorsal column nuclei and anterograde labeling of the ipsilateral lateral and dorsolateral nucleus basalis. Together these results define major somat osensory and auditory projections to the owl telencephalon that bypass the thalamus. Copyright (C) 2001 S. Karger AG. Basel.