Pre-Bout Neural Activity Changes in Premotor Nucleus HVC Correlate with Successful Initiation of Learned Song Sequence

Preparatory activity, characterized by gradual, longer timescale changes in neural activity, is present in a number of different brain areas before the onset of simple movements and is believed to be important for movement initiation. However, relatively little is known about such activity before initiation of naturally learned movement sequences. The song of an adult male zebra finch is a well studied example of a naturally learned movement sequence and previous studies have shown robust premotor activity immediately before song. Here, I characterize longer timescale changes in neural activity in adult male zebra finch premotor nucleus HVC before onset of song bouts. I show that interneurons and a subset of basal-ganglia-projecting neurons change their activity several hundred milliseconds before song bout onset. Interneurons increased their activity, whereas basal-ganglia-projecting neurons either increased or decreased their activity. Such changes in neural activity were larger, started earlier, and were more common specifically before song bouts that began with the short, repetitive, introductory notes (INs) characteristic of zebra finch song bouts. Further, stronger and earlier changes were also correlated with successful song sequence initiation. Finally, a small fraction of basal-ganglia-projecting neurons that increased their activity before song bout onset did not have song or IN-related activity, suggesting a specialized preparatory role for such neurons. Overall, these data suggest that pre-bout activity in HVC represents preparatory activity important for initiation of a naturally learned movement sequence.

SIGNIFICANCE STATEMENT Changes in neuronal activity well before the onset of simple movements are thought to be important for movement initiation. However, a number of animal movements consist of sequences of simple movements and relatively little is known about neuronal activity before such movement sequences. Using adult zebra finch song, a well studied example of a movement sequence, I show here that neurons in premotor nucleus HVC change their activity hundreds of milliseconds before song bout onset. In most neurons, the presence of such changes correlated with successful song sequence initiation. My results show the presence of preparatory neural activity in HVC and suggest a role for HVC in sequence initiation in addition to its established role in song sequence timing.