Language mastery goes native in the brain.

A core network of structures in the left hemisphere of the brain underwrites the understanding of a native language, whether it's spoken or signed, a new investigation finds. The data also suggest that initial experience with either English or sign language exerts specific effects on cerebral language organization.

Surprisingly, sign language comprehension is accompanied by substantial neuronal activity in parts of both the right and left hemispheres of native signers, reports psychologist David P. Corina of the University of Washington in Seattle.

"Our data imply that specialized language systems are established within the left hemisphere with the acquisition of a fully grammatical, natural language, even if it is not a spoken language," Corina contends. "But the right hemisphere is also involved in processing sign language." Corina and another participant in the international project, Daphne Bavelier of Georgetown University Medical Center in Washington, D.C., presented the findings last week at the annual meeting of the Society for Neuroscience in Washington, D.C.

Corina's group used functional magnetic resonance imaging to compare cerebral blood flow in volunteers as they read English sentences and random strings of consonants and as they watched the presentation of sentences and nonsense signs in American Sign Language. Elevated blood flow provides an indirect measure of surges in neural activity.

Participants consisted of eight hearing, native English speakers who did not know sign language, 16 native signers who had been deaf from birth but had learned English as young adults, and 13 hearing adults who were born to deaf parents and learned American Sign Language before acquiring English.

When reading English, both native speakers and hearing offspring of deaf parents displayed increased activity largely in left brain areas previously linked to language. Deaf signers exhibited patchy increases on both sides of the brain.

When interpreting signed sentences, deaf signers and hearing offspring of deaf parents experienced left brain activity boosts like those in native speakers reading English, as well as increased blood flow in the right brain. The activity in the right side reflects linguistic processing rather than simply the spatial analysis of signs, Bavelier argues.

"These data show that spoken language is part of a larger linguistic system in the brain," notes psychologist Ursula Bellugi of the Salk Institute in La Jolla, Calif. "The right hemisphere's role in processing sign language will need to be explained in future work."