Abstract
The nature of telencephalic control over premotor and motor circuits is debated. Hypotheses range from complete usurping of downstream circuitry to highly interactive mechanisms of control. We show theoretically and experimentally, that telencephalic song motor control in canaries is consistent with a highly interactive strategy. As predicted from a theoretical model of respiratory control, mild cooling of a forebrain nucleus (HVC) led to song stretching, but further cooling caused progressive restructuring of song, consistent with the hypothesis that respiratory gestures are subharmonic responses to a timescale present in the output of HVC. This interaction between a life-sustaining motor function (respiration) and telencephalic song motor control suggests a more general mechanism of how nonlinear integration of evolutionarily new brain structures into existing circuitry gives rise to diverse, new behavior.
Highlights
Complex behavior arises from motor instructions that are generated by interconnected networks of brain areas
In canaries (Serinus canaria), this model can account for all respiratory patterns underlying song and interprets the diverse respiratory patterns of different syllable types as the outcome of a nonlinear interaction between input from the telencephalon (HVC, RA) and internal dynamics of the respiratory pattern generators
The air sac pressure patterns during song were found to be consistent with the shapes and rhythms of the subharmonic solutions of a driven nonlinear system [2,12,13] similar to systems used by engineers and physicists for exploring complex behavior and chaos [14,15]
Summary
Complex behavior arises from motor instructions that are generated by interconnected networks of brain areas. The air sac pressure patterns during song were found to be consistent with the shapes and rhythms of the subharmonic solutions of a driven nonlinear system [2,12,13] similar to systems used by engineers and physicists for exploring complex behavior and chaos [14,15]. This interactive model is in clear contrast to one proposing more direct control by the telencephalic song control area HVC in the zebra finch (Taeniopygia guttata), such that all timescales present in the song arise directly from the output signal of this nucleus. Support for this model was derived from observations of sparsely coding output neurons in HVC [16,17] as well as experiments in which song was stretched by cooling of HVC [3,18]
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