Stimulation of the ventromedial prefrontal cortex and the perception of affective faces. An effective connectivity analysis.

The ventromedial prefrontal cortex is widely linked with emotional phenomena, including appraisal, modulation, and reward processing. Its perigenual part is suggested to mediate the appetitive value of stimulation. In our previous study, besides changes in evoked MEG responses, we were able to induce an apparent behavioral bias toward more positive valence while interpreting the ambiguous, morphed faces after the effect of excitatory tDCS stimulation of the perigenual ventromedial cortex (pgVM). In the present study, we reanalyze these data to reveal the importance of functional links between the vmPFC and other brain areas during the perception of emotional (fearful or happy) faces. Using the Directed Transfer Function method, we estimated MEG source-based effective connectivity on the 1.5 sec epochs during the passive presentation of facial stimuli in two counterbalanced sessions, preceded by either an excitatory or inhibitory tDCS session. We observed a prominent session effect as the connectivity changed after excitatory compared to inhibitory stimulation. These included increased outflows from the pgVM to most analyzed cortical regions, especially in the right hemisphere, a massive decrease in source activity in the right temporal region, and increased transfer of visual information towards many network nodes. Some interaction effects were also visible, with no involvement of the pgVM itself but with other nodes of the considered network. Overall, our data show that the stimulation focused at the pgVM elicited widespread network effects, including the areas mediating attention, visual processing, and emotions, as well as those associated with regulatory functions.