Understanding the characteristics of Introductory notes in the presence and absence of HVC

Abstract

The Introductory notes (IN), a series of identical vocal elements which are produced at the beginning of a zebra Finch song, is considered important for the initiation of the song. However, the brain region responsible for IN production is not known. HVC, a song premotor nucleus responsible for song production of which INs are also part of, is known to show neural activity just before INs are produced. Hence to study the role of HVC in IN production, HVC lesions were done and the post-lesion song was studied. Before that, to identify the presence of IN in post-lesion songs and study the effects of HVC lesion on IN, the characteristics of IN in normal birds in which HVC is present were quantified. We found that in a normal bird song INs has a high probability to appear at the first 2-3 positions of a song. The INs were found to have a definite set of acoustic properties which in general are similar to short calls and no other song syllables. Also, the first few positions in a song are distinct from other song syllables in terms of its duration and spacing. In the absence of HVC, the INs are no longer acoustically identical to normal INs, while the distinction of beginning few positions from other song syllables in terms of it duration and spacing remains the same as before. Thus, acoustic properties of INs is controlled by HVC, while the duration, initiation, and spacing of INs are independent of HVC.