It’s called transcranial direct-current stimulation (tDCS) and it involves applying mild electrical currents to the head.
TDCS belongs to a group of techniques known as ‘non-invasive brain stimulation’ because they don’t involve surgery. It is still experimental, but even in 2010, it was showing promise not only for alleviating pain, but for boosting the brain, improving memory and attention in healthy people. The US Department of Defense (DoD) wondered whether it might benefit military personnel. By the time Ryan became sick, Clark had led DoD-funded studies that explored this question, and produced remarkably good results.
Seems like this would be interesting to research for schizophrenia: