Timing matters: Transcranial direct current stimulation after extinction learning impairs subsequent fear extinction retention

Background: Transcranial direct current stimulation (tDCS) has previously been shown to improve fear extinction learning and retention when administered prior to or during extinction learning. This study investigates whether tDCS immediately following extinction learning improves efficacy of extinction memory retention. Methods: 30 participants completed a 2-day fear learning and extinction paradigm, where they acquired fear of a stimulus conditioned to an aversive electric shock on day 1. Extinction learning occurred on day 1, with tDCS or sham tDCS administered immediately following the learning phase. Participants returned for a second day test of extinction memory recall. Skin conductance was measured as the primary outcome. Results/Conclusions: Participants in the tDCS group showed impaired fear extinction retention on day 2, marked by significant generalisation of fear to the safety stimulus. This contrasts with earlier studies showing improved extinction retention when stimulation occurred during encoding of extinction learning, compared to immediate consolidation as in our study. These findings may have important implications for the use of tDCS during exposure therapy for anxiety and trauma disorders.