Transcranial direct current stimulation of the prefrontal cortex: a means to modulate fear memories

Targeting memory processes by noninvasive interventions is a potential gateway to modulate fear memories as shown by animal and human studies in recent years. Modulation of fear memories by noninvasive brain stimulation techniques might be an attractive approach, which, however, has not been examined so far. We investigated the effect of transcranial direct current stimulation (tDCS) applied to the right dorsolateral prefrontal cortex and left supraorbital region on fear memories in humans. Seventy-four young, healthy individuals were assigned randomly to two groups, which underwent fear conditioning with mild electric stimuli paired with a visual stimulus. Twenty-four hours later, both groups were shown a reminder of the conditioned fearful stimulus. Shortly thereafter, they received either tDCS (right prefrontal--anodal, left supraorbital--cathodal) for 20 min at 1 mA current intensity or sham stimulation. A day later, fear responses of both groups were compared by monitoring skin conductance. On day 3, during fear response assessment, the tDCS group had a significantly (P<0.05) higher mean skin conductance in comparison with the sham group. These results suggest that tDCS (right prefrontal--anodal, left supraorbital--cathodal) enhanced fear memories, possibly by influencing the prefrontal cortex-amygdala circuit underlying the memory for fear.