Body-stimuli related modulation of cognitive conflict induced by Midfrontal-occipital Ɵ-tACS

Mounting evidence from EEG and MEG studies reports that in correspondence of the medial frontal cortex (MFC) is possible to record an electrocortical signature in theta band (ϴ) named Midfrontal theta (MFϴ) that is associated with conflict and error processing and appears related to the temporal synchronization of frontal structures underlying the attempt to achieve top-down control. Interestingly, recent EEG studies reported also theta event-related synchronization increases for hands images processing under the occipito-temporal electrodes corresponding to the extrastriate body area (EBA). In the present single-blind, crossover, controlled, within-subject study, we applied ϴ-tACS (6Hz) over the MFC and over EBA while thirty-two healthy participants were asked to perform two variants of the Flanker task with stimuli representing either human-like hands (i.e. Hand-Flanker) or coloured-matched letters (i.e. Letter-Flanker). More specifically, we aimed at investigating whether: (i) the exogenous alternating current delivered in theta rhythm may modulate the long-range communication between neuronal populations underlying conflict monitoring and visuo-perceptual encoding of hand stimuli, and (ii) EBA, as a specialized cortical area involved in processing body-related stimuli, may play also a functional role in conflict processing. Results showed that response times were faster during correct performance when ϴ-tACS was delivered during the Hand-Flanker compared to γ-tACS (40Hz, gamma band, control frequency) and sham. Importantly, such an effect did not emerge in the Letter-Flanker indicating that theta oscillations over midfrontal-occipital areas did modulate bodily specific, stimulus content driven aspects of cognitive control.