The contribution of dorsolateral prefrontal cortex and temporoparietal areas in processing instrumental versus functional semantic violations in action representation

In the present study, we explored the contribution of different cortical areas in processing different semantic violations in action representation--that is, instrumental or functional violations. The cortical contribution in object-related action comprehension was verified by measuring changes in event-related potential (N400 effect), error rates (ERs), and response times (RTs), by applying an inhibitory transcranial direct current stimulation (tDCS) on the dorsolateral prefrontal cortex (DLPFC). Thirty-three subjects performed the detection task (action frames ending with a congruous vs. incongruous action). The tDCS effect was analyzed by comparing the N400, ERs, and RTs before and after stimulation. A significant reduction of the N400 and increased RTs were observed for incongruous stimuli in the case of inhibitory stimulation of the DLPFC. These results highlighted that DLPFC inhibition may limit the ability to analyze a semantically incongruous action, with a reduced N400 ERP effect and increased "cognitive costs" (higher RTs). Moreover, functional violation showed also the contribution of the temporoparietal areas to modulate the N400 amplitude. Therefore the existence of different cortical generators was supposed for the instrumental (more frontal) and the functional (more frontal and temporoparietal) semantic anomaly processing.