"When you give a medication, it goes everywhere in brain," Berman said. "But with techniques like tDCS, you can identify neuronal circuits that aren't functioning the way you want."
According to Berman, this is why tDCS is being explored as a treatment in various fields.
"You can vary this technique to target different circuits in the brain, depending on the illness," he said.
However, experts caution that more questions need to be answered before tDCS can be used clinically -- and especially at home, as some advocates have suggested.
"The study supports need for a multicenter study to look at duration of benefits and frequency of treatment," Pascuale-Leone said. "Even though side effects are benign, we still don't know about the long-term side effects that can happen after years of treatment with tDCS."
For now, staunch tDCS supporters like Fugedy -- and his patient, Koeing -- plan to stick to its off-label use.
"The most robust response I've seen is with depression," Fugedy said. "I see it, and I believe in it."
Koeing agreed, reporting that after using tDCS twice a week for the past four months, she has noted an "incredible improvement" in her mood.
"It just works," she said. "I don't need medications for depression anymore."