ORGANIZATION OF AFFERENT AND EFFERENT PROJECTIONS OF THE NUCLEUS BASALIS PROSENCEPHALI IN A PASSERINE, TAENIOPYGIA-GUTTATA

The connections of nucleus basalis (NB) of the rostral forebrain of th e zebra finch were investigated electrophysiologically and with antero grade and retrograde tracing methods to determine their functional org anization, the sources of their pontine afferents, and the targets of their telencephalic efferents. The nucleus was found to be partitioned into three major components, a rostral lingual part that received a h ypoglossal projection via a lateral subnucleus of the principal sensor y trigeminal nucleus (PrV), a middle beak part that received a trigemi nal projection via a medial subnucleus of PrV, and a caudal auditory p art that received a short latency auditory projection via the intermed iate nucleus of the lateral lemniscus. Beak NE also received a project ion from a paralateral lemniscal nucleus, and the dorsocaudal part of auditory NE and the medially adjacent neostriatum also received a proj ection from a lateral subnucleus of the superior vestibular nucleus (V S). The efferent projections of each of the three major parts of NE we re mainly to the adjacent neostriatum frontale (NF), which then provid ed projections to the lobus parolfactorius (exclusive of area X), the lateral archistriatum intermedium (Ail), and the lateral neostriatum c audale (NCl). Ail received a projection from NCI and provided terminal fields to the contralateral NCl and the NF. The major projections of Ail, however, descended bilaterally through the brainstem via the occi pitomesencephalic tracts, with dense terminations in the medial spirif orm nucleus and with extensive bilateral terminations throughout the l ateral reticular formation of the pens and medulla. For the most part, jaw, tongue, and tracheosyringeal motor nuclei did not receive termin ations. The results suggest that NE in zebra finch, like NE in pigeon and duck, is likely to be a major component of trigeminal sensorimotor circuitry involved in feeding and in other oral-manipulative behavior s. Results also show that the auditory component of NE is not directly linked to the vocal control system at telencephalic levels, but the p ossibility remains that the lingual, beak, and auditory parts of NE pl ay a role in vocalization by multisynaptic influences on cranial nerve motor nuclei innervating various parts of the vocal tract. (C) 1996 W iley-Liss, Inc.