Transcranial direct-current stimulation

Transcranial direct-current stimulation is a medical treatment that consists of using low voltage electricity running into electrodes attached to the head. Although it was once believed it could improve cognitive function, its sole known benefit is the treatment of clinical depression. It has fewer side effects than antidepressants, usually limited to headaches and irritation at the electrode connection sites. It's contraindicated for people who suffer from epilepsy.
Treatment generally lasts about 20 minutes, at which point the risk of side effects start to outweigh the benefits. Treatments are usually performed about once every two weeks.
Transcranial direct-current stimulation at Wikipedia