Sign language and pantomime production differentially engage frontal and parietal cortices

Abstract

We investigated the functional organization of neural systems supporting language production when the primary language articulators are also used for meaningful, but non-linguistic, expression such as pantomime. Fourteen hearing non-signers and 10 deaf native users of American Sign Language (ASL) participated in an H(2) (15)O-PET 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 "show how 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 non-handling 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 non-manipulable 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 non-signers 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 versus ASL verbs (even those that resemble pantomime) engage partially segregated neural systems that support praxic versus linguistic functions.

Figure 1

Illustration of sample object pictures and the verbs or pantomimes generated in response to these stimuli.

Figure 2

Results of the contrast between pantomime production and baseline task in the deaf participants (row A) and hearing non-signers (row B). Row C shows the results for the between subjects contrast (deaf – hearing non-signers) for the same task comparisons. The color overlay reflects significant increased activity at an uncorrected level, and regions in red reflect increased activity at a RFT corrected level (p < 0.05). Compared to the baseline task, pantomime production by both deaf and hearing participants resulted in greater activity in left superior parietal lobule. For the deaf participants, the increased activity was more extensive, encompassing the right parietal lobule, the left and right precentral gyrus, and right supplementary motor area.

Figure 3

Results of the contrast between handling verb generation and baseline task in the deaf participants (row A) and pantomime production (for the same ‘handling verb’ stimuli) and baseline task in hearing non-signers (row B). Row C shows the results for the between subjects contrast (deaf – hearing non-signers) for the same task comparisons. The color overlay reflects significant increased activity at an uncorrected level, and regions in red reflect increased activity at a RFT corrected level (p < 0.05). Increased activity in the inferior frontal gyrus is observed in the deaf signers but not the hearing participants.