A soft, 20-minute flow of electrons into both sides of the brain may cut violent impulses in half, according to a University of Pennsylvania study published Monday.

Transcranial direct-current stimulation was originally developed for people suffering from brain injuries, such as a stroke, or psychiatric conditions, such as depression. Roy Hamilton, a neurologist who directs Penn's Laboratory for Cognition and Neural Stimulation, where the new study was done, said the results "may be the first step towards helping people with pathological levels of aggression," but cautions that "we are a long way from being able to apply this."

The randomized, placebo-controlled study was conducted by a trio of criminologists and brain scientists.

>>READ MORE: In despair from major depression, I turned to a last resort: Magnets

The study enrolled 81 healthy Philadelphia men and women in their late teens and early 20s who randomly received either a single dose of the brain stimulation or a sham treatment. The next day, each was given a series of short stories to read describing physical or sexual aggression. Participants were asked to anticipate the likelihood that they would carry out the aggressive acts described in the stories. Responses ranged from zero (no chance at all) to 10 (absolutely certain).

On average, subjects who got the treatment were 47 percent less inclined to see themselves carrying out physical assault and 70 percent less inclined toward sexual assault. The effect was detected in both men and women, and did not depend on the subjects' past criminal history, if any.

Participants were also asked to judge how morally wrong it would be to act as the aggressor in the stories.

The treated group reported a small increase in moral queasiness over the prospect of sexual assault, compared with the placebo group. No change was detected for physical assault.

Roy Hamilton is researching non-invasive procedures for changing people’s mind.
Eric Sucar / University of Pennsylvania
Roy Hamilton is researching non-invasive procedures for changing people’s mind.

When given a lab test for aggressive behavior, subjects given the therapy behaved the same as the placebo group. On average, both groups used the same number of pins to stab at a voodoo doll on a screen. The authors acknowledged that "a single session […] may have a limited effect on behavioral change." They plan to try repeat sessions in the future.

The researchers chose to focus on adults without diagnosed psychopathy or major criminal records. "If an offender's brain is scanned, we don't really know if it's the brain deficit that leads to the behavior or if it's the other way around," said co-author Olivia Choy in a statement. "One of the main objectives of this study was to see whether there was a causal role of this brain region on antisocial behavior."

"Much of the focus in understanding causes of crime has been on social causation," said co-author Adrian Raine in a statement. "That's important, but research from brain imaging and genetics has also shown that half of the variance in violence can be chalked up to biological factors. We're trying to find benign biological interventions that society will accept, and transcranial direct-current stimulation is minimal risk. This isn't a frontal lobotomy."

"Historically we haven't taken this kind of approach to interventions around violence," Raine continued. "We only did one 20-minute session and we saw an effect. What if we had more sessions? What if we did it three times a week for a month?"

The team focused on a region of the brain near the temples called the dorsolateral prefrontal cortex, which had previously been linked to moral judgments, aggression, and antisocial behavior.

Were they jump-starting the moral center of the brain? "That's not really how brains work," noted Hamilton. Most complex thinking is scattered throughout the brain; the dorsolateral prefrontal cortex may be just "part of the constellation of brain areas that are engaged in moral judgment making."

Hamilton (who has applied current to his own brain "to make sure it wasn't noxious") said the procedure feels "tingly – kinda itchy, burny. I've heard people describe it as pinchy, too." None of the subjects dropped out due to discomfort.

Those assigned to get placebo treatments did receive an electric current, but only long enough (a few seconds) for them to think they might be getting the real therapy.

Hamilton believes low-current stimulation "nudges" brain cells closer to firing, rather than the more dramatic impact seen in shock therapy. "It's a very small effect," he said. "But multiply that times the millions and millions of cells that are constantly making that calculation."

Low-current brain stimulation has been studied for years, and is different from transcranial magnetic stimulation, which is increasingly being used to treat depression. A recent analysis by researchers from Europe, New Zealand, and the United States found that among high-quality studies involving more than a handful of subjects, low-current stimulation can offer limited benefits for depression, cravings, and fibromyalgia. It remains an experimental treatment in rehabilitation for stroke.