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Brain stimulation reduces aggression, boosts moral judgment in human trial

ABC Health logoABC Health 8/07/2018

© Provided by ABC Health Humans have been coursing current through our grey matter since Victorian times in a bid to supercharge our cognitive prowess.

Now, it appears that a zap to the right part of the brain can reduce aggressive intentions in adults.

A technique called transcranial direct-current stimulation — tDCS for short — passes a mild electrical current between electrodes on a person's scalp.

It is thought to increase or decrease the activity of brain tissue beneath.

In a study published today in the Journal of Neuroscience, a trio from the University of Pennsylvania used tDCS on healthy adults and found their aggressive intentions dropped by up to half the next day.

Still, don't expect to see tDCS added to violence rehabilitation programs soon, said study lead author Olivia Choy, a criminologist now at Singapore's Nanyang Technological University.

"It's still very, very early days."

Neuroscience of aggression

Dr Choy and her colleagues targeted a part of the brain called the dorsolateral prefrontal cortex.

It is associated with, among other things, aggression and moral decision-making.

They recruited 86 healthy adults and told them they would receive 20 minutes of tDCS.

But only half did. The other half — the placebo group — did not.

The next day, the subjects took a battery of tests to assess aggression, such as stabbing pins in a virtual voodoo doll.

Participants who received tDCS treatment showed less intention to commit hypothetical assault, and were more likely to perceive those acts as morally wrong, than the placebo group.

Early days yet

tDCS is already being trialled as a treatment for disorders such as depression and ADHD.

And while tDCS has promise, it can be difficult to get consistent results — even in the lab, said Jason Forte, a University of Melbourne cognitive neuroscientist who was not involved in the study.

Popping a couple of electrodes on a person's scalp and running current between them sounds like a fairly straightforward exercise to replicate, but there are loads of differences between people that can warp results.

Small differences in electrode placement, how much hair a person has, and even the thickness of their skull could all affect how much current ends up getting through to a specific part of the brain, Dr Forte said.

"The skull is a tremendously good electrical insulator," he said.

Any current that makes it past the skull into the brain may not be localised, said Melanie Emonson, a cognitive neuroscientist at Monash University.

The electrodes comprise a pair: an anode and a cathode.

"Current flows from the anode to the cathode, with the idea that brain activity under the anode is increased. But it's not as simple as that," Dr Emonson, who was not involved in the study, said.

"Current can diffuse through the brain in different ways."

The way the brain processes and manipulates information is incredibly complex, Dr Emonson said, with connections running between different areas.

"So just because you're targeting one area, it doesn't mean other brain regions are not being affected by the stimulation."

Then there is the critical question: what happens if tDCS is used on a person for months or years at a time?

Long-term effects unknown

"It's a huge concern," Dr Forte said. "Few studies have used long-term tDCS. It's completely unknown."

To use tDCS to induce long-term behaviour change without delving further into its effects, he added, "would be unethical".

Dr Choy acknowledged her study had limitations.

It used healthy adults, not groups of violent offenders.

And they only followed up the day after a single session of tDCS; so they do not know long the effect lasts.

"But that's certainly a question I hope future research will answer," Dr Choy said.

"If these findings can be replicated and extended, I think the use of tDCS on offenders is not entirely out of the question."

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