Pattern generator for repetitive avian vocalization: preliminary localization and functional characterization.

Electrical stimulation of the midbrain call areas was used to drive medullary neurons. Their activity was recorded with fine (25 mum) wire electrodes that allowed the nearer ones to be resolved as units. Syringeal (hypoglossal) motor neurons were identified by antidromic activation. Various units were turned on, speeded, slowed, stopped, or caused to fire in repetitive bursts. All units that were antidromically activated by hypoglossal stimulation fired in repetitive bursts with a rhythms which closely resembled that of calling. Many other units also fired in this bursting pattern, and the large majority of them were found at the obex or caudal to it despite extensive search rostrally. The nature of likely inputs to the medullary call neurons is discussed.