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Brain Adapts to Signing

by Carl Marziali
Hanna Damasio, co-director of the Brain and Creativity Institute

Persons fluent in American Sign Language have greater brain mass in the insula than non-signers, according to a recent study.

The insula is a part of the cerebral cortex associated with emotion, cravings and language. The latest findings further confirm that the insula is also involved in communication and that it is capable of adapting to the language demands placed on the brain.

“We have suspected that the insula is involved in many functions, and the new work confirms that idea,” said senior author Hanna Damasio, co-director of the Brain and Creativity Institute and the director of the Dornsife Imaging Center at USC College.

Damasio co-authored a widely-cited study, published in Science in 2007, that showed insula damage makes it easier for smokers to quit.

In this study, Damasio’s group found that both deaf and hearing signers have more white matter in the right insula than non-signers.

Deaf signers also have more gray matter in the posterior left insula than hearing subjects, the researchers found.

Gray matter contains neurons. White matter contains the nerves, or axons, that connect neurons to each other.

The researchers used magnetic resonance imaging to measure the volume of the insula in 25 congenitally deaf subjects, 25 hearing subjects with no knowledge of American Sign Language and 16 hearing subjects who grew up around deaf relatives and learned sign language at a young age.

The results were published online Nov. 12 in The Journal of Neuroscience.

“We interpreted the increase in white matter in the right insula as a possible result of the complexity of multisensory integration necessary for a signer, particularly a hearing signer, to produce both spoken language and sign language,” Damasio said.

“This is probably related to the fact that signers are regularly involved in a very demanding task.”

As for the larger volume of gray matter in the left insula of deaf subjects, Damasio said it could be a result of serving multiple processes, including visual, body-sensory and motor.

“For example, deaf signers do a lot of lip reading and visual perception of ASL signs made with the hands,” Damasio said.

Damasio’s co-authors were first author John Allen, associate professor of anthropology and senior fellow at the Brain and Creativity Institute; Karen Emmorey of San Diego State University; and Joel Bruss of the University of Iowa.

The National Institutes of Health funded the study.