rTMS on the left dorsolateral prefrontal cortex during an emotional memory task improves the performance of the retrieval process as function of level of anxiety and stimulus valence

Anxiety behaviour showed a consistent attentional bias toward negative and aversive memories, induced by a right prefrontal cortical superiority, based on an “unbalance effect” between the two hemispheres. In the present research we explored the contribution of the left dorsolateral prefrontal cortex (DLPFC) in memory retrieval process of positive vs. negative emotional stimulus, as a function of the anxiety level. The left DLPFC stimulation is supposed to modulate the “right superiority” in high level anxiety profile, by a decreasing of the attentional bias for negative cues. Material: Subjects, who were divided in two different groups depending on their anxiety level (high/low-anxiety, STAI), were required to perform a task consisting in two experimental phases: an encoding-phase (lists composed by positive and negative emotional words); and a retrieval-phase (old stimuli and new stimuli to be recognized). Moreover, new stimuli (distractors) were semantically related or unrelated to the old stimuli to test a possible interference effect induced by the semantic association. The left DLPFC effect was analyzed by using a high frequency rTMS (repeated transcranial magnetic stimulation) sham-controlled paradigm that induced a cortical activation of the left DLPFC. The rTMS stimulation over left DLPFC affected the memory retrieval, as a function of anxiety level and stimulus valence. High-anxiety subjects showed a typical attentional bias for aversive cues in comparison with low- anxiety subjects. However, they benefitted in greater measure to the prefrontal left stimulation with a reduced negative bias (increased accuracy and reduced RT for the positive stimuli) and a significant increased performance for the semantically related distractors (reduced interference effect). These results suggested that left DLPFC activation increases the memory retrieval of positive emotional information and might limit the “unbalance effect” induced by a right hemispheric superiority in high level of anxiety. Moreover, this effect was related to both retrieval of positive old memories and detection of semantically related distractors