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 thalamorecipient portion of Field 'L' (i.e. centered in Field L2a) in budgerigars at 3-5 weeks posthatching and as adults. The calls of birds sustaining Bas lesions before fledging, or as adults, were markedly abnormal in that they showed little frequency modulation and individual distinctiveness. 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 ventrolateral nucleus of the lateral lemniscus to Bas) and thalamotelencephalic (i.e., direct projections from nucleus ovoidalis thalami to Field L2a) auditory pathways in providing auditory feedback during vocal learning and performance are different and that the isthmofrontal pathway plays an essential role in these processes throughout the life of the animal.