An Avian Basal-Ganglia Forebrain Circuit Modulates the Reversal of Externally Reinforced Changes to Adult Zebra Finch Song

Abstract

Songbirds learn their songs through a trial and error process that shows remarkable similarities to human language learning, making them an ideal model for studying the neural substrates of vocal learning. Although adult zebra finch song is generally highly stable, a recent white noise aversive reinforcement learning paradigm has made it possible to shift the pitch of targeted song syllables. When aversive reinforcement is stopped, syllable pitch recovers to its stable baseline value over the course of several days. This recovery provides evidence that zebra finches are intrinsically motivated to match song performance to a previously memorized target version of the song. In this study, I tested the hypothesis that the lateral magnocellular nucleus of the anterior nidopallium (LMAN), a cortico-basal ganglia outflow nucleus implicated in both juvenile and externally reinforced adult learning, is necessary for intrinsically motivated pitch recovery. I drove down the fundamental frequency of targeted song syllables using white noise aversive reinforcement. I then performed bilateral electrolytic lesions of LMAN to determine whether normal pitch recovery would take place without LMAN activity. All three birds lesioned demonstrated significantly reduced recovery rates, providing convincing preliminary evidence that LMAN is implicated in song recovery. However, these results were not conclusive due to small sample size and the lack of histological data to verify lesion efficacy. Further characterization of the role of LMAN in pitch recovery could provide a valuable context for explaining phenomena associated with human language re-learning, such as how stroke victims might have difficulty recovering speech, or how adults are able access and easily re-learn elements of languages to which they were exposed during early childhood.