Modulation of prefrontal theta oscillations slows social cognition.

Mentalization, the ability to interpret the mental states of others, is a central component of Theory of Mind (ToM). The medial prefrontal cortex (mPFC) has been consistently implicated in mentalization, but the neural oscillations that support this process are not fully understood. Theta oscillations are a candidate mechanism, because they have been linked to social-cognitive processing and may coordinate information processing through coupling with faster gamma activity. In the present sham-controlled, within-subjects study, we investigated whether mentalizing performance can be modulated using either conventional theta transcranial alternating current stimulation (tACS) or cross-frequency theta-gamma tACS over the mPFC. Thirty-four participants completed a mentalization task during theta, theta-gamma, and sham stimulation. Decision time and accuracy were assessed for affective and cognitive judgments. Theta stimulation slowed decision times compared with sham and theta-gamma stimulation, whereas theta-gamma stimulation did not differ from sham. Theta stimulation slowed both affective and cognitive judgments, with the effect being more pronounced for cognitive judgments. Accuracy was unaffected by stimulation. The observed slowing suggests that theta stimulation may have increased the weighting of competing social information, resulting in slower affective and cognitive judgments rather than improved performance. Together, these findings indicate that mPFC theta oscillations may influence the speed of mentalizing judgments.