Transcranial Direct Current Stimulation and Fear Extinction

Psychiatric disorders characterized by pathological fear and anxiety are common and often disabling. Despite their limitations, exposure therapies are among the most efficacious treatments for these disorders. Extinction learning is thought to be a core mechanism of therapeutic exposure. Extinction learning is mediated by a well-defined circuit encompassing the medial prefrontal cortex (mPFC), amygdala, and hippocampus. This raises the exciting possibility that direct engagement of this circuitry might enhance the response to therapeutic exposure. Transcranial direct current stimulation (tDCS) is a neuromodulation technology that can augment brain plasticity, learning, and memory. The proposed study will evaluate whether tDCS can engage extinction circuitry, and improve extinction learning and memory. This study will enroll psychiatrically healthy volunteers to test whether tDCS applied to the mPFC can augment spontaneous mPFC activity, engagement of extinction circuitry during extinction learning and recall, and classically-conditioned extinction learning and memory. Healthy volunteers will complete a standardized, three-day fear conditioning and extinction learning and memory task. On day 1, participants will complete a fear conditioning task. On day 2, participants will receive sham (placebo) or active tDCS prior to completing a fear extinction learning task. On day 3, participants will complete an extinction recall task. Electrodermal activity and heart rate will be continuously monitored during the conditioning and extinction procedures to assess autonomic arousal. All procedures will be completed in a magnetic resonance imaging (MRI) scanner; imaging data will be collected before and after tDCS and during all conditioning and extinction procedures.