中国科学院行为科学重点实验室知识库

Semantic processing is an amodal process with modality-specific information integrated in supramodal ‘convergence zones’ or ‘semantic hub’ with executive mechanisms that tailor semantic representation in a task-appropriate way. One unsolved question is how frontal control region dynamically interacts with temporal representation region in semantic integration. The present study addressed this issue by using inhibitory double-pulse transcranial magnetic stimulation (TMS) over the left inferior frontal gyrus (IFG) or left posterior middle temporal gyrus (pMTG) in one of eight 40-ms time windows (TWs) (3 TWs before and 5 TWs after the identification point of speech), when human participants (12 females, 14 males) were presented with semantically congruent or incongruent gesture-speech pairs but merely identified the gender of speech. We found a TW-selective disruption of gesture-speech integration, indexed by the semantic congruency effect (i.e., a cost of reaction time due to semantic conflict), when stimulating the left pMTG in TW1, TW2 and TW7, whereas when stimulating the left IFG in TW3 and TW6. Based on the timing relationship, we hypothesize a two-stage gesture-speech integration circuit with a pMTG-to-IFG sequential involvement in the pre-lexical stage for activating gesture semantics and top-down constraining the phonological processing of speech. In the post-lexical stage, an IFG-to-pMTG feedback signal might be implicated for the control of goal-directed representations and multimodal semantic unification. Our findings provide new insights into the dynamic brain network of multimodal semantic processing by causally revealing the temporal dynamics of frontal control and temporal representation regions.