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|The Psychologist News - A mushroom fuelled trip in a brain scanner|
A mushroom fuelled trip in a brain scanner
The whimsical flights and darker episodes of psychedelic experience have been studied before in detail, but the neural correlates of these experiences are largely unknown. For a new study, 30 participants took a mushroom-fuelled trip inside a brain scanner as part of the first ever fMRI study of the psychedelic state (PNAS: tinyurl.com/86whqj8).
The research team was led by Robin Carhart-Harris at Imperial College, London, and included David Nutt, the former head of the UK's Advisory Council on the Misuse of Drugs. The researchers used fMRI to observe brain changes in participants as they were injected intravenously with psilocybin, the active compound in magic mushrooms.
Two fMRI techniques were used. One relied on the BOLD response. This is the conventional fMRI methodology, which uses changes in the oxygenation of cerebral blood as a marker for local brain-activity fluctuations. The other technique involved arterial spin labelling, which reveals changes in cerebral blood flow. In both cases, participants rested in the scanner as they were infused either with a moderate dose of psilocybin or a placebo. During the scans participants used a button to indicate the subjective intensity of their experience and afterwards they provided more detailed feedback. All psychedelic experiences (including 'I saw my surroundings change in unusual ways' and 'my imagination was extremely vivid') were rated higher in the psilocybin condition, with the exception of 'I felt afraid' and 'I felt paranoid'.
Both imaging techniques produce complementary results. Taking psilocybin was associated with widespread reductions in brain activity and reduced blood flow in a raft of cortical and subcortical regions. There was also marked decoupling between the posterior cingulate cortex and the medial prefrontal cortex - key hubs in the default mode network, which is thought to be involved in consciousness and self-referential processing. Moreover, participants' subjective reports of trip intensity correlated with the observed regional decreases in neural activity.
Carhart-Harris and his colleagues noted that their findings contradicted the popular assumption that psychedelic drugs increase neural activity. However, they said the widespread dampening of brain activity was consistent with reports of the potential therapeutic benefits of taking psychedelic compounds. For example, depression is associated with heightened medial prefrontal cortex activity - a state that returns to normal after successful treatment.
'These studies offer the most detailed account to date of how the psychedelic state is produced in the brain,' the researchers concluded. 'The results suggest decreased activity and connectivity in the brain's connector hubs, permitting an unconstrained style of cognition.'
-- Christian Jarrett
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