FUNCTIONAL-ANATOMY OF FOREBRAIN AUDITORY PATHWAYS IN THE BUDGERIGAR (MELOPSITTACUS-UNDULATUS)

Interconnections of forebrain auditory and vocal control nuclei were m apped in the budgerigar using pathway tracing techniques. The anatomic al results indicate four circuits by which auditory information may in fluence the vocal motor system: (1) direct auditory thalamic projectio ns from nucleus dorsomedialis posterior (DMP) to both the neostriatal higher vocal center (HVC) and robust archistriatal nucleus (RA); (2) d irect projections from a neostriatal projection field of DMP (i.e., MA N, the magnocellular nucleus of the neostriatum) to HVC and RA; (3) pr ojections from DMP and other 'accessory' auditory thalamic nuclei to t he ventral paleostriatum (VP), which in turn projects to MAN and RA; ( 4) projections to HVC from the lateral hyperstriatum ventrale (HV), wh ich receives input from nucleus basalis (Pas) as well as from the oval nucleus of the HV (HVo), which receives direct input from RA. Lesion methods were used to evaluate the roles of auditory pathways in call l earning and production. The results show that pathways associated with Bas are essential for call production in both adult and unfledged bud gerigars, while VP efferents influence vocalization only in young, unf ledged budgerigars. Lesions centered in either the primary auditory ne ostriatum (Field L2a) or the neostriatal area in receipt of Field L in put (the ventrolateral neostriatum intermedium or NIVL) did not affect vocalization in juvenile or adult budgerigars.