Single Session of tACS in a Depressive Episode

Participants will report for a study visit and will review and sign a consent form. Participants will complete several clinical assessments and also take a urine drug test and urine pregnancy test (if applicable). Eligibility will be re-assessed by the investigators before the participant moves on to the next phase. If the participant still qualifies, the participant will first be fitted with two 5x5cm electrodes placed over F3/F4 (10-20 measurement system) and one 5x7cm electrode placed over Cz. In addition, the participant will have a 128-channel EEG net placed on their head. Participants will provide a saliva sample to assess for brain-derived neurotrophic factor (BDNF), which may affect how the participant's brain responds to stimulation. Once the participant is fitted with this equipment, the participant will complete two interactive EEG tasks, then 2-minute resting state EEG with the participant's eyes closed, then a 5-minute resting state EEG with the participant's eyes open. Following these recordings, participants will respond to additional questionnaires. Immediately following this, the participant will receive 40 minutes of stimulation (tACS or sham tACS). During this stimulation, participants will sit comfortably upright and awake. After stimulation has completed, participants will respond to additional questionnaires. Once completed, participants will then complete an additional 5-minute resting state EEG with the participant's eyes open, as well as complete one of the additional interactive EEG tasks. Finally, participants will respond to a blinding questionnaire to assess if the participant thought that the participant received stimulation. Once complete, the participant will leave. This session is estimated to last about 4 hours.