VISUAL AND SOMATOSENSORY INPUTS TO THE AVIAN SONG SYSTEM VIA NUCLEUS UVAEFORMIS (UVA) AND A COMPARISON WITH THE PROJECTIONS OF A SIMILAR THALAMIC NUCLEUS IN A NONSONGBIRD, COLUMBA-LIVIA

Nucleus uvaeformis (Uva), previously identified as a component of song control circuitry in songbirds, and nucleus dorsolateralis posterior thalami, pars caudalis (DLPc) in pigeon, were compared with respect to their relative positions in the dorsolateral part of the posterior th alamus, their cell types, and their afferent and efferent projections. Both nuclei are closely related to the habenulointerpeduncular tract, have similar cell types, and receive a dense projection from deep lay ers of the optic tectum, predominantly ipsilaterally, and a distinct p rojection from the dorsal column and external cuneate nuclei, predomin antly contralaterally. Recordings of multiple unit activity evoked by visual and somatosensory stimuli were used to guide injections of trac er into either DLPc or Uva, and the projections to the telencephalon w ere charted. Both nuclei were found to have a major terminal field in the medial part of the ipsilateral neostriatum intermedium (NI), known as nucleus interfacialis (NIf) in songbirds, and a minor terminal fie ld in the roof of the neostriatum caudale (NC). In pigeon, the DLPc te rminations in NC were within a region known as neostriatum dorsale (Nd ), and, in male songbirds, the Uva terminations were in the high vocal center (HVC): Recordings of visual and somatosensory evoked activity were then used to guide injections of tracer into NI, and the afferent and efferent projections were again compared in pigeon and songbirds. The projections from either DLPc or Uva were confirmed, and terminal fields were observed either in Nd in pigeon, the dorsolateral part of NC in female songbirds, or HVC in male songbirds, Injections df tracer into either Nd or HVC confirmed their sources of afferents in DLPc or Uva, respectively, and in NI, but there was incomplete overlap of the distribution of retrogradely labelled cells in NI and the terminal fi elds of DLPc or Uva. It is concluded that DLPc and Uva are comparable nuclei having similar afferent and efferent projections relaying visua l and somatosensory information to the telencephalon, The possible rol e of this information in vocal control is discussed. (C) 1994 Wiley-Li ss, Inc.