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Zapping the brain to relieve depression can spark fits of fury in a small number of people, psychiatrists warn.

Transcranial direct current stimulation (tDCS) is increasingly being used to treat a range of conditions, from depression and addiction to obsessive-compulsive disorder (OCD). In it, electrodes attached to the scalp emit weak currents that help strengthen electrical brain circuits.

To treat depression, the current is usually applied to the left dorsolateral prefrontal cortex – a brain area involved in regulating the emotions. There is now good evidence that this lifts mood in some people.

However, it also appears to trigger anger in rare cases, say �����Ի��� at Taipei City Hospital in Taiwan.

They recently reported two people at their psychiatric facility who had uncharacteristic outbursts of fury after receiving tDCS.

Urge to ‘tear everything apart’

The first was a 39-year-old woman with severe depression, low energy and suicidal thoughts who hadn’t responded to antidepressants. Straight after tDCS treatment, she became agitated, began yelling angrily and felt the urge to “tear everything apart”.

The woman had no previous record of angry behaviour and returned to normal after 4 hours. Her depression score improved from 42 to 17 on a 60-point scale over the next four weeks. She had no further episodes of rage, but said she still felt slightly restless and “keyed up” with energy eight weeks after treatment.

The second case was a 28-year-old woman with major depression and OCD who hadn’t benefited from antidepressants and could barely leave her home. Hours after her second session of tDCS, she became intensely angry and began loudly cursing, crying and fist clenching. The same thing happened after her third session.

The woman’s normally passive personality returned after 30 minutes and she had no further attacks. Her depression score dropped from 23 to 16 after four weeks and her OCD symptoms also improved.

 at the University of Cambridge says she has witnessed a single case of tDCS-related anger in her research of more than 100 people undergoing the treatment. A woman with depression reported uncharacteristic feelings of rage during almost all of her eight tDCS sessions.

Real or placebo?

The reason for this phenomenon is a mystery, says Nord. Hung and Huang believe the treatment may cause a surge of the brain’s dopamine reward system in some people’s brains, leading to behavioural excitability and anger, but this is purely speculative. “It would be impossible to know the neural basis of this switch because no one has ever examined it,” says Nord.

It is also unclear why only a handful of people are affected, although it is common for psychiatric treatments to have mixed effects, Nord says. “Because tDCS only alleviates depression in a subset of patients, it also may only cause side effects in specific patients, explaining why this side effect, if it is real, is very rare,” she says.

One possibility is that the rage attacks are actually a placebo effect, says Nord. She has found that just as many side effects are reported by people who receive fake tDCS as by those who receive the real thing. “This is because they are receiving an unusual intervention and so they are hyper-aware of any changes they might experience as a result,” she says.

Further research will help to tease out whether tDCS-related anger is caused by biological or placebo factors and identify who is most at risk, says Nord. “My hope is that with more reports like this, the field may be able to parse out individual differences that make a patient more or less likely to experience it.”