Modulation of Gestural-verbal Semantic Integration by tDCS

- We explored the hemispheric asymmetries of gestural-verbal integration.
- Symbolic gestures served as primes for verbal targets.
- Anodal tDCS of right but not left IFG improved symbolic gestures processing.
- Right IFG facilitation was selective to gestures and not the control task.
- Gesture comprehension may be enhanced by improved gesture-language integration.

BackgroundUnderstanding actions based on either language or observation of gestures is presumed to involve the motor system, and reflect the engagement of an embodied conceptual network. The role of the left inferior frontal gyrus (IFG) in language tasks is well established, but the role of the right hemisphere is unclear with some imaging evidence suggesting right IFG activation when gestures mismatch speech.ObjectiveUsing transcranial direct current stimulation (tDCS), we explored the hemispheric asymmetries in the assumed cognitive embodiment required for gestural-verbal integration.MethodsSymbolic gestures served as primes for verbal targets. Primes were clips of symbolic gestures taken from a rich set of emblems and pantomimes. Participants responded by performing a semantic relatedness-judgment under 3 stimulation conditions - anodal tDCS (atDCS) over the left IFG, atDCS over the right IFG, and sham. There was also a non-semantic control task of attentional load.ResultsAtDCS of the right IFG generated faster responses to symbolic gestures than atDCS over the left IFG or sham stimulation. For the attentional load task, no differences were observed across the three stimulation conditions. These results support a right-lateralization bias of the human mirror neuron system in processing gestural-verbal stimuli.ConclusionGesture comprehension may be enhanced by improved gesture and language integration.