Department of Neurobiology, Duke University Medical Center, Durham, North Carolina 27710, USA
Address for correspondence: Eric D. Jarvis, Department of Neurology, Duke University Medical Center, Box 3209, Durham, NC 27710, USA. Voice: 919-681-1680; fax: 919-681-08772.
jarvis{at}neuro.duke.edu;
http://www.jarvislab.net/
Ann. N.Y. Acad. Sci. 1016: 749-777 (2004).
Vocal learning, the substrate for human language, is a rare
trait found to date in only three distantly related groups of
mammals (humans, bats, and cetaceans) and three distantly related
groups of birds (parrots, hummingbirds, and songbirds). Brain
pathways for vocal learning have been studied in the three bird
groups and in humans. Here I present a hypothesis on the relationships
and evolution of brain pathways for vocal learning among birds
and humans. The three vocal learning bird groups each appear
to have seven similar but not identical cerebral vocal nuclei
distributed into two vocal pathways, one posterior and one anterior.
Humans also appear to have a posterior vocal pathway, which
includes projections from the face motor cortex to brainstem
vocal lower motor neurons, and an anterior vocal pathway, which
includes a strip of premotor cortex, the anterior basal ganglia,
and the anterior thalamus. These vocal pathways are not found
in vocal non-learning birds or mammals, but are similar to brain
pathways used for other types of learning. Thus, I argue that
if vocal learning evolved independently among birds and humans,
then it did so under strong genetic constraints of a pre-existing
basic neural network of the vertebrate brain.
