Abstract
Action comprehension that is related to language or gestural integration has been shown to engage the motor system in the brain, thus providing preliminary evidence for the gestural-verbal embodiment concept. Based on the involvement of the sensorimotor cortex (M1) in language processing, we aimed to further explore its role in the cognitive embodiment necessary for gestural-verbal integration. As such, we applied anodal (excitatory) and sham transcranial direct current stimulation (tDCS) over the left M1 (with reference electrode over the contralateral supraorbital region) during a gestural-verbal integration task where subjects had to make a decision about the semantic congruency of the gesture (prime) and the word (target). We used a cross-over within-subject design in young subjects. Attentional load and simple reaction time (RT) tasks served as control conditions, applied during stimulation (order of three tasks was counterbalanced). Our results showed that anodal (atDCS) compared to sham tDCS (stDCS) reduced RTs in the gestural-verbal integration task, specifically for incongruent pairs of gestures and verbal expressions, with no effect on control task performance. Our findings provide evidence for the involvement of the sensorimotor system in gestural-verbal integration performance. Further, our results suggest that functional modulation induced by sensorimotor tDCS may be specific to gestural-verbal integration. Future studies should now evaluate the modulatory effect of tDCS on semantic congruency by using tDCS over additional brain regions and include assessments of neural connectivity.
Highlights
The engagement of the sensorimotor system in word comprehension has been an intriguing question in brain research (Hauk et al, 2004; Tettamanti et al, 2005; Pulvermuller and Fadiga, 2010; Vukovic et al, 2017)
Gestures that could not be identified by participants because of their cultural specificity were omitted after task versions validation
We found that atDCS led to significantly faster correct answers compared to stDCS, but only atDCS, anodal transcranial direct current stimulation (tDCS); stDCS, sham tDCS
Summary
The engagement of the sensorimotor system in word comprehension has been an intriguing question in brain research (Hauk et al, 2004; Tettamanti et al, 2005; Pulvermuller and Fadiga, 2010; Vukovic et al, 2017). Studies have reported activation in the primary motor cortex during word comprehension when words involved sensorimotor features (Willems and Hagoort, 2007; Pulvermuller and Fadiga, 2010), using various methodological approaches. These approaches include functional magnetic resonance imaging (fMRI; Kemmerer et al, 2008; Kana et al, 2012, 2015), electroencephalography (Mollo et al, 2016; Schaller et al, 2017) and magnetoencephalography (Klepp et al, 2015; Mollo et al, 2016). Activation of the same fronto-parietal sensorimotor areas in both observing and executing an action enables an individual to understand the observed action more (Rizzolatti et al, 2001)
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