Abstract:
The Bengalese finch's song is made up of a limited set of syllables arranged in variable sequences, including two key types of branchpoint syllables: convergent syllables are the syllables that are preceded by different syllables, whereas divergent syllables are the syllables that are followed by different syllables. Prior studies have shown that the acoustic properties of these branchpoint syllables vary depending on the syllable that precedes or follows it, but the relationship between these variations and respiratory control is poorly understood. This study examines the correlation between the acoustic properties of branchpoint syllables and respiratory pressure during singing in Bengalese finches (n=6 birds). We observed differences in peak inspiratory pressure and expiratory waveforms before and after the branchpoint syllables, suggesting a link between respiratory control and syllable transitions. To explore the origins of these differences, we compared expiratory waveforms in three ways: (1) aligned to syllable onset, (2) aligned to syllable offset, and (3) time-warped to the median duration of the syllable. The highest correlation was found in waveforms aligned to syllable offset, indicating that respiratory timing is closely linked to syllable transitions. To understand the neural control of respiration, I recorded in motor nucleus RA (robust nucleus of the arcopallium) in anesthetized Bengalese finches. Dorsal parts of RA project to respiratory motor neurons while the ventral parts of RA project to syringeal motor neurons. RA projection neurons show tonic spontaneous activity and my results reveal lower spontaneous firing rates in dorsal vs ventral RA with the Inter Spike Intervals decreasing from dorsal to ventral. This might correspond to their specialized functional roles. Overall, my results suggest variation in respiration pressure for branchpoint syllables and differences in spontaneous firing in dorsal and ventral RA, suggesting potential functional differences in the control of respiratory and syringeal muscles.
