Rhythmic Syllable-Related Activity in a Songbird Motor Thalamic Nucleus Necessary for Learned Vocalizations

Abstract

Birdsong is a complex behavior that exhibits hierarchical organization. It is hypothesized that the hierarchical organization of birdsong is the result of activity in the avian song circuit that selects and activates behavioral units in a specific order. While the representation of singing behavior has been studied in some detail in ‘cortical premotor circuits,’ little is known of the role of the thalamus in the organization of adult birdsong. Using a combination of behavioral and electrophysiological studies, we examined the role of the thalamic nucleus Uvaeformis (Uva) in the production of stereotyped, adult song. Complete bilateral lesions of Uva result in a loss of stereotyped acoustic and temporal structure, similar to earlier reports of the effects of HVC lesions. Notably, Uva lesions result in a broad, nearly exponential distribution of syllable durations, characteristic of early vocal babbling. Using a motorized microdrive, we recorded multiunit activity in Uva during singing in adult birds. We find that neural activity in Uva exhibits significant 10Hz rhythmicity locked to song syllables, increasing prior to syllable onsets and decreasing prior to syllable offsets—a pattern of activity observed in HVC during adult and juvenile song. These results suggest that the avian song is functionally organized around a 10Hz rhythm, with one cycle of the 10Hz rhythm being the fundamental ‘unit’ of song.