UCSF

The neuromodulator acetylcholine has a well-establi¬shed role in enhancing sensory perception in states of heightened arousal, but whether acetylcholine acts centrally to exert an analogous influence on behavioral outputs is largely unknown. Here we use the quantifiable nature of birdsong to investigate how cholinergic tone modulates the cortical song premotor nucleus HVC, and influences vocal output. We found that dialysis of the cholinergic agonist carbachol into HVC enhanced the vigor of vocal output by increasing the pitch, tempo, amplitude and stereotypy of song. These effects did not require input from basal-ganglia circuitry, indicating direct cholinergic modulation of song premotor circuitry. Moreover, blockade of muscarinic acetylcholine receptors in HVC attenuated natural increases in vigor observed when song is directed at females in a courtship context. Neural recordings revealed that both dialysis of carbachol and courtship song were associated with higher firing rates in HVC, with conspicuous enhancement of low-frequency activity locked to the underlying rhythm of song. Further, neural activity in HVC predicted behavioral variability on a trial-by-trial basis, consistent with the possibility that natural variation in cholinergic tone influences acoustic output. Our findings establish that acetylcholine exerts a potent influence on forebrain premotor circuitry that acts to invigorate motor output, and indicates that such modulation contributes to the natural invigoration of song during courtship.