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Psilocybin, a compound found in magic mushrooms, could help patients with depression that can't be treated with standard antidepressants or talking therapies. Rob & Ann Simpson/Getty Images

A psychedelic trip can 'reset' the brain of people with severe, treatment-resistant depression, improving their symptoms in half of patients within just five weeks.

This is the first time the aftereffects of psilocybin – the active component of magic mushrooms – have been mapped in the brain. Researchers at Imperial College London found that one of the key brain circuits involved in depression 'disintegrated' during the trip, and reintegrated in a new way in the following weeks. The findings are published in a study in the journal Scientific Reports.

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This brain circuit – known as the default mode network – is involved in a range of essential functions, such as consciousness and our sense of self. In people with depression, the default mode network goes into overdrive, previous studies have shown.

The Imperial study was the first to take a look at what happens next, after the trip. A total of 19 patients took part in the study. They all had depression that didn't respond to conventional antidepressants or talking therapies. They had brain scans the day after they were given a dose of psilocybin, and then again five weeks later.

"After treatment with psilocybin, the default mode network became reintegrated. It showed a slight increase in its stability or integrity," study author Robin Carhart-Harris told IBTimes UK. "Curiously, its spatial extent widened slightly as well."

Studies since the 1950s have suggested that psilocybin and other 'classic psychedelics', such as LSD, could be used to alleviate depression and anxiety. But exactly how the drug changes the brain to treat these mental health conditions has been unclear.

The study suggests that the therapeutic benefit could be from 'resetting' the brain, particularly the default mode network. The study participants themselves, without prompting from the researchers, used words like reset, rebooted, refreshed and even defragged – a process to declutter a computer's hard drive – to describe how the treatment had made them feel.

About half of the patients with otherwise treatment-resistant depression showed a significant improvement after five weeks. This shows promise for a new therapeutic treatment for depression coupled with psychological support, Carhart-Harris says.

A large trial of psilocybin for treatment-resistant depression, for which Carhart-Harris is an adviser, is being proposed by the healthcare company Compass Pathways. It aims to recruit about 400 patients with severe depression in several European countries, to see if psilocybin could work in a clinical setting.