The improvement of positive emotional memories for target and distractor words through the rTMS stimulation of left DLPFC

The prefrontal cortex is supposed to be crucial in emotion-memory integration: it was shown to be particularly sensitive to the encoding and retrieval of emotional contents. Furthermore, the valence model of emotional cue processing may explain the distinct role of the left and right hemisphere involvement in positive/negative valenced emotional information recall. The present research explores the role of the dorsolateral prefrontal cortex (DLPFC) in memory retrieval process of positive vs. negative emotional stimuli when old (target) and new (distractor, semantically related and unrelated to the target) stimuli were presented. A rTMS (repeated Transcranial Magnetic Stimulation) paradigm inducing an increased cortical activation of the left DLPFC was used. Subjects were required to perform a task consisting in an encoding-phase, where some lists composed by positive and negative emotional words were presented to the subjects; and a retrieval-phase, where a recognition performance on the old stimuli and the new stimuli were required during the rTMS stimulation over the left DLPFC. We found that the rTMS stimulation over this area affects the memory retrieval efficiency (shorter Response Times) of positive emotional material. Moreover, related and unrelated distractors were better discarded when they were positively valenced, specifically related distractors were recognized with an increased effectiveness (better accuracy) and efficiency (reduced RTs). This result suggested that left DLPFC activation favour the memory retrieval of positive emotional information and that it is able to induce a more appropriate selective process to distinguish target from distractor stimuli.