Song-selective auditory input to a forebrain vocal control nucleus in the zebra finch.

Neurons in nuclei on the motor pathway for vocalizations in songbirds are known to respond to sound stimuli. The auditory responses in one such nucleus, robustus archistriatalis (RA), were characterized by making multi-unit recordings in awake and anesthetized adult male zebra finches and in birds that had received lesions of the input to RA from the lateral part of the magnocellular nucleus of the anterior neostriatum (LMAN) or the Higher Vocal Center (HVC). In awake birds, RA neurons have a high level of spontaneous activity and vigorous auditory responses to song stimuli. Significantly greater responses are seen to the bird's own song (BOS) than to BOS played in reverse (REV) or to the songs of conspecifics (CON). Under ketamine-xylazine anesthesia, spontaneous activity is reduced, response latency increases and responses to BOS, REV and CON are indistinguishable. Responses obtained under urethane anesthesia are similar to those seen in awake birds. Thus, the pattern and selectivity of auditory responses in RA depend on the animal's state. Auditory responses in RA are qualitatively unchanged following lesion of the input to RA from LMAN, indicating that this pathway is not required for the sensory processing that underlies the preference for BOS on the vocal production pathway. Our results show that an input other than that from LMAN must be primarily responsible for auditory responses in RA. The direct projection from HVC is the most likely pathway by which song selective auditory information arrives in RA, since lesioning HVC abolished auditory responses in RA.