Erich Jarvis (Duke University)
Venue: Room 218, Henry Wellcome Building
Date: 7th September 2009
Time: 13:00 - 14:00
Understanding how the brain controls complex behavioral traits has been a mysterious question in the field of science for generations. One such complex trait is vocal learning, a critical behavioral substrate for song in song learning birds and spoken language in humans. A common feature for species that have this trait is that they have forebrain and brainstem systems that control vocalizations, whereas those that produce only innate sounds have only the brainstem vocal systems. Using behavioral, molecular, electrophysiological, and anatomical approaches we have found that the song brain systems of distantly related song learning birds are embedded within a motor system that is involved limb and body movements in all birds. The song learning and adjacent motor systems share many properties in common, including motor-driven gene expression cascades and connectivity into two sub-networks – an anterior pathway that in songbirds is involved in song learning and a posterior pathway that is involved in song production. Comparative analyses with human brain systems for spoken language, suggested that these parallels exist in them as well. Based on these and other findings, we propose a motor theory for the origin of vocal learning, where unique brain systems used to learn and produce song and spoken language evolved out of a pre-existing system that control movement and motor learning. We further propose these brain systems follow a fundamental design in tetrapod vertebrates consisting of the two motor sub-pathways (anterior and posterior) of the vertebrate brain that during development form parallels systems that control different muscle groups, and are innervated by sensory systems for feedback control of different motor behaviors. When vocal learning evolves, this pre-existing motor system is then connected to muscles of the vocal organ (syrinx in birds, larynx in humans) to control a specialized form of learned movement for song and speech. In this manner, the evolution of brain pathways for vocal learning can evolve independently of a common ancestor, but dependent on the pre-existence of a motor pathway neural substrate. We suggest that this could be a possible mechanism for evolution of complex behavioral traits beyond vocal learning.
Host: Tom Smulders