The contribution of LMAN, the output of an avian basal ganglia-forebrain circuit to song variability and adaptive plasticity in the adult Bengalese finch
The capacity for change in adult behavior and in the adult brain is much greater than previously thought. In songbirds, adult behavior continues to change measurably even after song is well-learned and stable. Whether adult song change serves any function, however, is under debate. LMAN, the output of a basal-ganglia forebrain pathway in the song system, has been broadly implicated in adult song change including adult song variability and sensory feedback plasticity. For adult song variability, previous studies have shown that loss of LMAN by lesion or inactivation reduces variability in syllable structure. These findings, however, have been limited due to the low variability present in the most common songbird species of study, the zebra finch. For adult plasticity, it has been shown that LMAN can prevent degradation in song before auditory feedback manipulations. Although this suggests active regulation of adult song change, it is unclear whether the role of LMAN is adaptive under these circumstances. Here, we have investigated the role of LMAN in the adult Bengalese finch in both adult song variability and adult song plasticity. We first find that adult Bengalese finch retains and modulates a significant amount of variability in song, including variability in syllable structure and variability in syllable sequencing. We then show that LMAN is involved in the regulation of one specific aspect of song variability: syllable structure. Finally, using a new behavioral paradigm for adult plasticity, we extend these findings to demonstrate that LMAN is involved in adaptive recovery of song following injury. Taken together, these data suggest that LMAN in the adult Bengalese finch retains a strong capacity for actively driving adult song change, and that its function remains adaptive long after learning is complete.