COMPARISON OF THE EFFECTS OF LESIONS IN NUCLEUS BASALIS AND FIELD-L ON VOCAL LEARNING AND PERFORMANCE IN THE BUDGERIGAR (MELOPSITTACUS-UNDULATUS)

Lesions were placed in either nucleus basalis (Bas) or the primary tha lamorecipient portion of Field 'L' (i.e. centered in Field L2a) in bud gerigars at 3-5 weeks posthatching and as adults. The calls of birds s ustaining Bas lesions before fledging, or as adults, were markedly abn ormal in that they showed little frequency modulation and individual d istinctiveness. Call durations, however, were similar for lesioned and unlesioned birds. In contrast, the calls of Field 'L' lesioned birds were similar to those of siblings and cagemates. This implies that the roles of the isthmofrontal (i.e., direct projections from the ventrol ateral nucleus of the lateral lemniscus to Bas) and thalamotelencephal ic (i.e., direct projections from nucleus ovoidalis thalami to Field L 2a) auditory pathways in providing auditory feedback during vocal lear ning and performance are different and that the isthmofrontal pathway plays an essential role in these processes throughout the life of the animal.