UCSF

Song production in birds requires planning on two different time-frames: the immediate muscle program for the vocal effectors (vocal and respiratory musculature), as well as the more temporally extended control of sequencing the shorter vocal elements (syllables) into longer vocalizations. The songs of the Bengalese finch exhibit variability in both dimensions: syllables are produced with a small amount of variability from rendition to rendition, and the syllables themselves can be used in a variety of sequences. The following research examines three question in regards to variability in Bengalese finch song.

1. Does a syllable's sequence affect its phonology?

2. Are changes in phonology are a result of differences in brain activity?

3. Is there a correlation between changes in brain activity and changes in phonology?

In analyzing the songs of Bengalese finches, we find that syllable structure is altered by sequence in two different ways: syllable production is modified by the immediate history of the system, as well as long time-scale patterns in the sequencing of syllables. These sequence effects upon syllable production are not the result of purely peripheral influences, however. There are multiple ways in which changes to central neural activity correlate with changes in syllable phonology. Changes in the activity of the robust nucleus of the arcopallium (RA) neurons were correlated with mean changes in syllable production, as well as with changes to syllable production around the mean. The correlation between mean changes in RA activity and syllable structure implies that the RA motor program is phonological in nature. We also find that RA activity correlates specifically with changes in syllable features such as pitch, amplitude and entropy. In taking these results together, a more complete model of syllable control by RA can be constructed. The data suggest that general patterns in RA activity relate to the identity of individual syllables, and that changes in syllable structure are made by increasing or decreasing that activity of specific pools of RA neurons. The results of this research are the first demonstration of phonological encoding by RA neurons.