Editors' ChoiceNeuroscience

Higher Consciousness

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Science Translational Medicine  22 Feb 2012:
Vol. 4, Issue 122, pp. 122ec31
DOI: 10.1126/scitranslmed.3003870

Psychedelic drugs such as “magic mushrooms” have been used for centuries in religious ceremonies and more recently have been investigated for potential therapeutic effects in psychiatry. Although there are extensive anecdotal descriptions of the effects of psychedelic drugs, there is little known about which neural brain circuits are affected. It is tempting to imagine that these “mind-expanding” drugs activate dormant brain areas and fuel connections that cannot be accessed during waking life. Now, Carhart-Harris and colleagues put this lore to rest by demonstrating that the psychedelic drug psilocybin is associated with reduced cerebral blood flow in the brain and functional disconnection of key brain areas.

Healthy volunteers who had prior experience with psychedelic drugs underwent a functional magnetic resonance imaging (fMRI) protocol under the influence of psilocybin, the primary psychoactive component of hallucinogenic mushrooms. Analysis of cerebral blood flow before and after taking the drug revealed reductions in blood flow in key subcortical areas such as the thalamus, as well as in cortical regions such as the prefrontal and posterior cingulate cortex. Most of the reduced blood flow was observed in higher association areas rather than in primary sensory areas. Importantly, communication between the prefrontal and posterior cingulate cortices appeared to be uncoupled as subjects transitioned from the waking state to the psychedelic state.

These findings undermine the prior assumption that psychedelic drugs lead to brain activation and furthermore suggest that the coupling of critical hubs in human brain networks regulates normal waking consciousness. The fact that psilocybin can uncouple cognitive modules to facilitate “higher” consciousness has important therapeutic implications. Psychiatric disorders such as depression have been posited to result from overly stable brain networks with impaired flexibility. Psychedelic or similarly psychoactive drugs may one day be able to uncouple rigid neural connections and provide a return to the versatile processing required for normal conscious experience.

R. L. Carhart-Harris et al., Neural correlates of the psychedelic state as determined by fMRI studies with psilocybin. Proc. Natl. Acad. Sci. U.S.A. 109, 2138–2143 (2012). [Abstract]

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