Context, transparency and culture in motor resonance phenomena: Causal evidence of the motor cortex

A connection between language and movement information in metaphorical and literal expressions activates the motor system. Despite numerous studies exploring distinctions between idioms and metaphors, a notable research gap remains in the specific effect of idioms with different transparency levels concerning motor resonance. Our primary focus was analysing the functional role of the primary motor cortex (M1) in processing hand motor verbs both in literal expressions and in two idiomatic contexts, i.e., opaque and transparent idioms. Additionally, we explored a potential language and cultural effect by comparing Turkish and Spanish speakers. An overt priming task with self-paced reading was used to judge the relatedness of a primer and a target sentence. We implemented a repetitive transcranial magnetic stimulation (TMS) protocol using continuous theta-burst stimulation (cTBS) compared to sham stimulation over the M1 in both Turkish and Spanish native speakers prior to the experimental task. Our findings reveal that the performance of Turkish and Spanish participants in processing hand motor actions was facilitated after the application of cTBS over the left M1. Moreover, brain stimulation specifically facilitated the processing of only transparent-but not opaque-idioms in both Spanish and Turkish participants. Our study reports distinct motor resonance results between different types of idioms with a parallel cross-cultural effect.