Context-Dependent Changes in Pre-Bout Activity in Adult Male Zebra Finch HVC

Abstract

Motor preparation is essential for the efficient execution of any motor activity. Prior studies mostly focused on motor preparation before artificially trained motor movements, but the nature of motor preparation before natural, ethologically relevant animal movements remains poorly understood. The zebra finch song is a more ethologically relevant, naturally learned motor sequence consisting of a stereotyped pattern of vocalizations. A song-bout often starts with short vocalizations called introductory notes (INs), followed by a group of syllables called a song motif, which can be repeated one or more times. Two distinct pathways in the brain primarily control song- 1) the Song motor pathway consisting of the song premotor region HVC, downstream nucleus RA, which connects to the avian vocal organ and respiratory muscles, and 2) the Anterior forebrain pathway, which consists of the indirect projection from HVC to RA via the basal ganglia homolog Area-X. Previous studies have shown pre-song-bout activity in HVC hundreds of milliseconds prior to undirected songs, which are songs produced by the bird in isolation. This was suggested to have a role in motor preparation. Zebra finches also produce directed songs in the presence of a female bird. Directed songs are faster and more stereotyped than undirected songs, and directed song-bouts begin with more INs. Whether there are changes in activity before directed song-bouts remains unclear. My thesis focused on examining the context-dependent differences (directed vs. undirected song) in the pre-bout activity. I did not find differences in the average pre-bout firing rate between the two contexts, but I found differences in the latency of change in pre-bout firing. Relative to song-bout onset, the change in pre-bout firing occurred slightly later before directed songs in comparison to the undirected songs. Additionally, directed songs contain more INs, which are suggested to have a preparatory role. My findings suggest a continuum between pre-bout activity and INs, suggesting they may have a shared preparatory role before song onset. Another possibility is that there is a difference in state that causes a sudden abrupt increase in pre-bout activity before directed songs in comparison to the slowly increasing activity before undirected songs.