Frequency control during song does not require syringeal muscles in the Great Kiskadee

A. AMADOR, F. GOLLER AND G.B. MINDLIN.

San Diego, California, EEUU

Conferencia; Society for Neuroscience 37th Annual Meeting.; 2007

Society for Neuroscience (SFN)

In the last years, songbirds have been widely studied, as animal models for vocal learning. For this reason, the motor control of their phonating organ (the syrinx) has been explored in detail. An important acoustic feature of the resulting vocalization is the time variation of its fundamental frequency, which presents a variety of patterns across different syllables. In oscines, experimental and theoretical studies have shown that the fundamental frequency is correlated with the activity of ventral muscles that can change the tension of the oscillating labia. The suboscines are taxonomically close to the oscines, but are thought to develop vocal behavior innately.Here we present the first physiological study of the song of the Great Kiskadee (Pitangus sulphuratus), which consists of three stereotyped syllables. We recorded air sac pressure and sound during spontaneously generated song. In all the songs and calls recorded, the modulations of the fundamental frequency and the air sac pressure are highly correlated. To test whether this correlation is a result of coordinated neural instructions to the peripheral system or a result of the interaction of the peripheral system, we denervated the syringeal muscles by bilateral resection of the tracheosyringeal branch of the hypoglossal nerve. After the surgery, the similarity between fundamental frequencies and pressure patterns remained. Quantification of these data in pressure versus frequency plots indicates a single linear relationship in the intact and denervated birds.The lack of an obvious role for the syringeal muscles in the frequency control is surprising, taking into account its strong role in oscine birds. Therefore, we explored a mechanism for transducing pressure into frequency. We implemented the two mass model, commonly used for voice production, which is designed to mimic the dynamics of oscillating membranes with structure. We add the hypothesis of a nonlinear restitution force for the oscillating labia. We show that the synthetic sound that is obtained when the model is driven by the experimentally recorded air sac pressure is in good agreement with the bird s song. With all these results, we show that the time evolution of a syllable s fundamental frequency can be interpreted as the transduction of a respiratory motor pattern into frequency through a biomechanical property of syringeal labia.