P1086: DLPFC and left supramarginal gyrus increases the recognition of instrumental and functional violations in transitive action representation

The correct outcome of transitive actions depends on an object’s, use considering both the instrumental and functional features. Indeed, the representation of object-related action includes the correct/incorrect instrumental use and the congruous/incongruous functional use of the object. Objectives: The contribution of frontal (dorsolateral prefrontal cortex, DLPFC, experiment 1) and posterior supramarginal gyrus, experiment 2) areas to process these semantic violations (instrumental vs. functional) in action semantic representation was explored. Methods: The DLPFC and supramarginal gyrus activity was appositely modulated by tDCS (transcranial direct current stimulation). The effect of tDCS (anodal, excitatory) when subjects processed congruous/incongruous object-related actions was verified by measuring the modulation of the ERs (Error Rates) and RTs (Response Times). Forty-three subjects performed the detection task within a dynamic context (video tapes representing a sequence of four action frames ending with a congruous vs. incongruous action). Results: Significantly decreased RTs were observed for incongruous stimuli in the case of DLPFC stimulation compared to the sham condition. This effect was related to both the instrumental and functional semantic violations, suggesting that the activation of the DLPFC may increase the ability to analyse the semantic anomaly independently from the anomaly type, which would limit the cognitive costs. In contrast, parietal stimulation reduced RTs only in response to functional semantic violations. Conclusion: Thus, different cortical contributions by anterior vs. posterior areas occurred in response to semantic anomalies respectively for generic expectancy violations (more frontally distributed) and specific functional violations (more frontally distributed).