A left-prefrontal lateralized, sympathetic mechanism directs attention towards social threat in humans: evidence from repetitive transcranial magnetic stimulation.

The prioritized processing of threat is suggested to be motivated by anxiety, regulated by the parasympatheticus, and biased to the right hemisphere. However, according to an anterior dimensional model of negative affect this is unlikely to be true when threat is of social origin. Social threat is communicated by the angry facial expression, and recent research indicates that prioritized processing of angry faces is motivated by anger. Anger is a sympathetically dominated emotion, and for its expression and experience, neuroimaging data have demonstrated anterior lateralization to the left hemisphere. To scrutinize the above diverging statements, suprathreshold low-frequency repetitive transcranial magnetic stimulation (rTMS) was applied over the right and the left prefrontal cortex (PFC) of ten healthy subjects during 15min continuously, and the subsequent effects on sympathetic and parasympathetic activity of the heart, and selective attention to angry facial expressions were investigated. Combined rTMS-neuroimaging studies have shown contralateral excitation after unilateral supratheshold low-frequency rTMS, hence the strengthening of contralaterally mediated emotion functions. The earlier reported increases in selective attention to angry facial expressions after right-PFC rTMS were found to be accompanied by and significantly associated with elevations in sympathetic activity. Our data suggest that a left-PFC lateralized, sympathetic mechanism directs attention towards the angry facial expression.