Abstract
The present study investigated emotional memory following bilateral transcranial electrical stimulation (direct current of 1 mA, for 20 minutes) over fronto-temporal cortical areas of healthy participants during the encoding of images that differed in affective arousal and valence. The main result was a significant interaction between the side of anodal stimulation and image emotional valence. Specifically, right anodal/left cathodal stimulation selectively facilitated the recall of pleasant images with respect to both unpleasant and neutral images whereas left anodal/right cathodal stimulation selectively facilitated the recall of unpleasant images with respect to both pleasant and neutral images. From a theoretical perspective, this double dissociation between the side of anodal stimulation and the advantage in the memory performance for a specific type of stimulus depending on its pleasantness supported the specific-valence hypothesis of emotional processes, which assumes a specialization of the right hemisphere in processing unpleasant stimuli and a specialization of the left hemisphere in processing pleasant stimuli. From a methodological point of view, first we found tDCS effects strictly dependent on the stimulus category, and second a pattern of results in line with an interfering and inhibitory account of anodal stimulation on memory performance. These findings need to be carefully considered in applied contexts, such as the rehabilitation of altered emotional processing or eye-witness memory, and deserve to be further investigated in order to understand their underlying mechanisms of action.
Highlights
In the present study we examined the effects of Transcranial Direct Current Stimulation on emotional memory
The first Analysis of Variance (ANOVA), testing possible differences in recall percentages depending on image emotional arousal, revealed a significant main effect of the factor Category of Image (F(1,11) = 17.32, p = 0.0016), emotional pictures being remembered better than non-emotional ones (61.63% and 51.04%, respectively), corroborating the solid effect of emotional arousal in enhancing memory performance
In the present Transcranial Direct Current Stimulation (tDCS) study, healthy volunteers received frontotemporal stimulation of both cerebral hemispheres during the encoding of pictures with different affective arousal and valence, in order to measure its effects on a following free recall task
Summary
In the present study we examined the effects of Transcranial Direct Current Stimulation (tDCS) on emotional memory. The specific contribution of each cerebral hemisphere in emotional stimuli processing continues to be controversial, and two main hypotheses have been proposed concerning the involvement of the left and right prefrontal regions. Much evidence supports the right-hemisphere hypothesis, which assumes that the right hemisphere is specialized in processing all emotional stimuli, independently of their pleasantness [12]. A number of convincing data suggest a valence-specific organization of emotional perception, with the left hemisphere specialized in processing pleasant and positive emotions and the right hemisphere specialized in unpleasant and negative ones [13,14,15]
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