Sign language and pantomime production differentially engage frontal and parietal cortices

We investigated the functional organisation of neural systems supporting language production when the primary language articulators are also used for meaningful, but nonlinguistic, expression such as pantomime. Fourteen hearing nonsigners and 10 deaf native users of American Sign Language (ASL) participated in an (H2O)-O-15-positron emission tomography study in which they generated action pantomimes or ASL verbs in response to pictures of tools and manipulable objects. For pantomime generation, participants were instructed to showhow you would use the object. For verb generation, signers were asked to generate a verb related to the object. The objects for this condition were selected to elicit handling verbs that resemble pantomime (e.g., TO-HAMMER, hand configuration and movement mimic the act of hammering) and nonhandling verbs that do not (e.g., POUR-SYRUP, produced with a Y handshape). For the baseline task, participants viewed pictures of manipulable objects and an occasional nonmanipulable object and decided whether the objects could be handled, gesturing yes (thumbs up) or no (hand wave). Relative to baseline, generation of ASL verbs engaged left inferior frontal cortex, but when nonsigners produced pantomimes for the same objects, no frontal activation was observed. Both groups recruited left parietal cortex during pantomime production. However, for deaf signers the activation was more extensive and bilateral, which may reflect a more complex and integrated neural representation of hand actions. We conclude that the production of pantomime vs. ASL verbs (even those that resemble pantomime) engages partially segregated neural systems that support praxic vs. linguistic functions.