Respiratory Control and Neurophysiology
In waterslager canaries, which produce most syllables using the left syrinx, as soon as a unilaterally produced syllable finishes, the right side opens briefly to allow inspiratory airflow through both bronchi before being closed again for left syrinx song production. During this “mini-breath” the left side may remain partially or fully adducted, allowing less inspiratory airflow than the right side while remaining ready to quickly resume singing.
When bilateral airflow and subsyringeal air sac pressure were monitored along with electromyographic activity of expiratory abdominal muscles in brown thrashers (Toxostoma rufum), it was observed that during unilateral production of song, expiratory abdominal muscle activity was the same on both sides. This indicates that while inspiration and syringeal song control may be lateralized, motor control of respiratory muscles possibly remains bilateral.
Muscles of the syrinx are controlled by the tracheosyringeal branch of the hypoglossal nerve. Each syringeal half is ipsilaterally innervated by the hypoglossal motor nucleus (XIIts) in the brain, which in turn receives projections—mainly ipsilateral—from nucleus robustus (RA), an important song control nucleus that also regulates respiratory muscles. Laterality of song control has been observed all the way into the higher vocal center (HVC) brain region; unilateral lesions to HVC produce lateralized effects in the temporal patterning of song in the zebra finch. Also see Bird song: Neurophysiology
Read more about this topic: Lateralization Of Bird Song
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