P165. Effects of transcranial direct current stimulation on training cognitive control over emotional distraction

Abstract

Various psychiatric disorders are characterised by insufficient cognitive control on emotion processing. Patients with major depressive disorder (MDD) show a biased attention towards negative information, which leads to impaired cognitive abilities. Previous studies have shown that the dorsolateral prefrontal cortex (dlPFC) is critically involved in cognitive control processes. In MDD the dlPFC has been found to be hypoactivated during emotion processing. Modulating the activity of the dlPFC with noninvasive brain stimulation could be a tool for ameliorating cognitive control in patients. In the present study we use transcranial direct current stimulation (tDCS) over the dlPFC to modulate cognitive control during the training of a working memory task with emotional content. We further assess the activity of the dlPFC with near infrared spectroscopy (NIRS) in order to understand its role during emotion control. In our main experience (EXP I), 24 healthy individuals performed three sessions of a delayed response working memory task (DWM) with pictures of varying content (negative vs. neutral) presented during the delay period. During the first session dlPFC activity was recorded via NIRS. In the second session, participants either received 20 min of 1 mA anodal tDCS or sham stimulation. In the third session, the stimulation condition was reversed. A second experiment (EXP II) with the same task and session number was conducted with 16 other healthy participants in order to observe activation changes of the dlPFC throughout the DWM training. No stimulation was applied during this second experience, but NIRS was recorded during all three sessions. In both experiments, an attentional bias (longer response times after negative distractors) was found in the first DWM session. In EXP I, anodal tDCS over the dlPFC increased working memory performance when neutral distractors were present. In EXP II we found that while the attentional bias was eliminated by training, the activity of the dlPFC during negative compared to neutral distractors increased. Therefore, the tDCS-induced performance increase specifically with neutral distractors could be explained by lower dlPFC activation in the neutral as compared to the negative distractor condition in the course of repeated DWM sessions. This lower prefrontal activity might be more susceptible to anodal, activity increasing tDCS than the higher prefrontal activity observed during the negative condition.