Study to examine the extent to which neurophysiological states recorded for a specific person on one day can be induced on a subsequent day

The study will be a single-arm design. It involves a longitudinal design in which subjective, physiological, and brain reactivity will be measured on 3 occasions, between ~2 weeks and ~4 months apart. The first assessment will be on a subjectively "good" day (mood rating above 7/10). The second will be on a subjectively "bad" day (mood rating below 3/10) and the third will be within a week of the second session. At the second and third sessions, participants will work to "restore" their brain state to that of the first assessment.

Inclusion Criteria:

• Adults age 18-65
• have periods of good and bad moods each lasting at least 2 days

Exclusion Criteria:

• Refusal or inability to provide informed consent
• People who report being in frank psychotic episodes or who say they are unable to stay off psychoactive substances during assessments will be excluded. Because we do not want to return participants to manic states, individuals with bipolar I disorder who report being or appear to be in a manic state at their baseline assessment will also be excluded.
• Inability to complete questionnaires written in English. The justification is that many of the primary analyses involve assessment of change in self-reported symptoms using measures normed in English. Participants must thus be able to read those measures to give valid indications of the extent to which they have responded to the intervention.
• Chronic pain that could be exacerbated by electrical stimulation
• Having difficulties in corrected vision or hearing which would prevent efficient processing of the experimental stimuli
• Having a North American Adult Reading Test (NAART) equivalent full scale IQ < 85
• History of a convulsive disorder
• Presence of any neurologic disorder or medication therapy known to decrease seizure threshold (e.g., brain injury, frequent/severe headaches).
• Participants deemed "not a good fit" for the study for other reasons (such as, but not limited to, continually arriving late or rescheduling, not being a trustworthy historian or accurate reporter of symptoms, being belligerent with study staff, or presenting an active suicide risk) can also be excluded.
• Heart condition
• Current severe Diagnostic and Statistical Manual of Mental Disorders (DSM-V) alcohol or substance use disorder, with the exception of nicotine or caffeine. Clinician will access subjects' alcohol and substance use on a case-by-case to determine whether specific cases of mild or moderate alcohol or substance use would also interfere with the effects of the intervention.
• Those who have metal implants in the vicinity of stimulated areas, or who have electrical implants (e.g., pacemakers, vagus nerve stimulator) will be excluded out of an abundance of caution regarding the safety of electrical stimulation.
• Any metal implant or subcutaneous metal in the face or head