An avian basal ganglia - forebrain circuit contributes differentially to syllable 1 versus sequence variability of adult

27 28 Behavioral variability is important for motor skill learning but continues to be 29 present and actively regulated even in well-learned adult behaviors. In adult songbirds, 30 two types of song variability can persist and are modulated by social context: variability 31 in syllable structure and variability in syllable sequencing. The degree to which the 32 control of both types of adult variability is shared or distinct remains unknown. The 33 output of a basal ganglia-forebrain circuit, LMAN (the lateral magnocellular nucleus of 34 the anterior nidopallium), has been implicated in song variability. For example, in adult 35 zebra finches, neurons in LMAN actively control the variability of syllable structure. It is 36 unclear, however, whether LMAN contributes to variability in adult syllable sequencing 37 because sequence variability in adult zebra finch song is minimal. In contrast, 38 Bengalese finches retain variability in both syllable structure and syllable sequencing 39 into adulthood. We analyzed the effects of LMAN lesions on the variability of syllable 40 structure and sequencing and on the social modulation of these forms of variability in 41 adult Bengalese finches. We found that lesions of LMAN significantly reduced the 42 variability of syllable structure but not of syllable sequencing. We also found that LMAN 43 lesions eliminated the social modulation of the variability of syllable structure but did not 44 detect significant effects on the modulation of sequence variability. These results 45 demonstrate that LMAN contributes differentially to syllable versus sequence variability 46 of adult song and suggest that these forms of variability are regulated by distinct neural 47 pathways. 48 49