NEURAL PATHWAYS FOR THE CONTROL OF BIRDSONG PRODUCTION

As in humans, song production in birds involves the intricate coordina tion of at least three major groups of muscles: namely, those of the s yrinx, the respiratory apparatus, and the upper vocal tract, including the jaw. The pathway in songbirds that controls the syrinx originates in the telencephalon and projects via the occipitomesencephalic tract directly upon vocal motoneurons in the medulla. Activity in this path way configures the syrinx into phonatory positions for the production of species typical vocalizations. Another component of this pathway me diates control of respiration during vocalization, since it projects u pon both expiratory and inspiratory groups of premotor neurons in the ventrolateral medulla, as well as upon several other nuclei en route. This pathway appears to be primarily involved with the control of the temporal pattern of song, but is also importantly involved in the cont rol of vocal intensity, mediated via air sac pressure. There are exten sive interconnections between the vocal and respiratory pathways, espe cially at brain-stem levels, and it may be these that ensure the neces sary temporal coordination of syringeal and respiratory activity. The pathway mediating control of the jaw appears to be different from thos e mediating control of the syrinx and respiratory muscles. It originat es in a different part of the archistriatum and projects upon premotor neurons in the medulla that appear to be separate from those projecti ng upon the syringeal motor nucleus. The separateness of this pathway may reflect the imperfect correlation of jaw movements with the dynami c and acoustic features of song. The brainstem pathways mediating cont rol of vocalization and respiration in songbirds have distinct similar ities to those in mammals such as cats and monkeys. However, songbirds , like humans, but unlike most other non-songbirds, have developed a t elencephalic vocal control system for the production of learned vocali zations. (C) 1997 John Wiley & Sons, Inc.