The executive control network is involved in novel situations or those in which prepotent responses need to be overridden. Previous studies have demonstrated that when control is exerted, conscious perception is impaired, and this effect is related to the functional connectivity of fronto-parietal regions. In the present study, we explored the causal involvement of one of the nodes of this fronto-parietal network (the right Supplementary Motor Area, SMA) in the interaction between executive control and conscious perception. Participants performed a dual task in which they responded to a Stroop task while detecting the presence/absence of a near-threshold Gabor stimulus. Concurrently, transcranial magnetic stimulation (TMS) was applied over the right SMA or a control site (vertex; Experiment 1). As a further control, the right Frontal Eye Field (FEF) was stimulated in Experiment 2. Diffusion-weighted imaging (DWI) tractography was used to isolate the three branches of the superior longitudinal fasciculus (SLF I, II and III), and the frontal aslant tract (FAT), and to explore if TMS effects were related to their micro- and macrostructural characteristics. Results demonstrated reduced perceptual sensitivity on incongruent as compared to congruent Stroop trials. A causal role of the right SMA on the modulation of perceptual sensitivity by executive control was only demonstrated when the microstructure of the right SLF III or the left FAT were taken into account. The volume of the right SLF III was also related to the modulation of response criterion by executive control when the right FEF was stimulated. These results add evidence in favor of shared neural correlates for attention and conscious perception in fronto-parietal regions and highlight the role of white matter in TMS effects.
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