Forgetting fear associations through tES: Which memory process might be critical?

We read with interest the article by Abend and colleagues1 titled 'Modulation of fear extinction processes using transcranial electrical stimulation', which adds relevant insights to the extremely limited literature on the effect of non-invasive brain stimulation on fear extinction mechanisms. Given the interest in using brain stimulation for treatment of anxiety disorders and post-traumatic stress disorder, research examining the impact of non-invasive brain stimulation on mechanisms involved in the maintenance and treatment of these disorders is critical. In their study, Abend and colleagues examined the effects of two different types of non-invasive transcranial electrical stimulation (tES; that is, direct current (DC) and alternating current (AC) stimulation) on fear extinction processes in healthy humans to assess a potential relevance/application of these protocols in therapeutic context. Thus, the authors decided to test three separate groups of participants (that is, DC, AC and Sham stimulation) by targeting the medial prefrontal cortex, which is known to mediate fear extinction mechanisms (for example, Milad and Quirk2), in a 3-day protocol. On the basis of previous research, they expected that excitability-enhancing anodal tDCS over the ventromedial prefrontal cortex would improve extinction, most probably via activation of GABAergic neurons of the amygdala,3 and that low-frequency tACS during extinction might reduce fear memory consolidation via long-term depression-like effects. Skin conductance and self-report responses were examined to assess the effect of the provided treatments in fear extinction.