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Psilocybin and Brain Function

A brain imaging study of psilocybin revealed unexpected findings.

This post is in response to
Psilocybin and Personality

As reported in a previous article, a number of fascinating studies recently have focused on the effects of the drug psilocybin, a classic psychedelic drug. Scientists still do not have a good understanding of the brain mechanisms by which psilocybin produces its effects. A recent study used brain scanning (specifically, functional magnetic resonance imaging) to obtain a window into the brain of 30 volunteers injected with this drug in order to understand what happens during the transition between normal waking consciousness and the onset of drug effects (Carhart-Harris et al., 2012). The researchers were surprised to discover that drug effects were associated with decreases in activity in a number of key brain areas, rather than the expected increase. This finding has led to speculations about the relationship between brain activity and mystical states experienced under psychedelic drugs. However, the actual implications of the study’s findings are far from clear.

In this study, participants received two brain scans each, once after receiving a saline injection, and once after receiving a psilocybin injection. The effects on brain activity were then compared. After receiving psilocybin brain blood flow decreased, indicating reduced activity. In particular, activity in areas regarded as important network hubs that maintain the connectivity of the various areas of the brain showed the most consistent deactivation. These areas are known as the medial prefrontal cortex (mPFC) and the posterior cingulate cortex (PCC). (If you’re put off by neuroscience please don’t quit reading just yet! I’ll try to keep the brain science as simple as possible.) These two areas appear to play important roles in the regulation of self-awareness as they are particularly activated when people are asked to think about themselves for example (Wicker, Ruby, Royet, & Fonlupt, 2003). The authors thought it was quite interesting that these areas actually show much higher activity than other parts of the brain under normal conditions, yet showed the greatest deactivation under the drug. Additionally, the intensity of the alterations of conscious experience reported by the volunteers was proportional to the decrease in brain activity. That is, the more brain activity decreased, the more vivid the “trip” experienced.

Why psilocybin might induce reductions in brain activity is not known, but it is natural to speculate. The authors argued that the findings are consistent with Aldous Huxley’s idea that normal consciousness acts like a “reducing valve” that actually constrains how much information a person normally takes in, so that one is not overwhelmed by chaotic stimuli. Therefore, the apparent “mind-expanding” effect of psychedelic drugs is due to a relaxation of this constraining effect. The reduced activity of the brains connector hubs might permit an “unconstrained style of cognition” producing psychedelic effects (Carhart-Harris, et al., 2012).

In an article for Time magazine, Carhart-Harris takes these speculations even further. Under high doses of psilocybin many people experience a sense of ego-transcendence in which the boundaries of the self appear to dissolve resulting in a blissful state of oneness with the universe. As noted earlier, areas of the brain associated with self-awareness, the mPFC and the PCC, showed a marked reduction in activity under psilocybin. This could imply that ego-transcendence might be facilitated by reduced activity in these brain areas. This idea seems appealing when considering that contemplative traditions aim to produce ego-transcendence by quietening the mind.

However, let’s not jump to conclusions just yet. There is a potential problem with Carhart-Harris et al.’s interpretation of their results that they appear to have overlooked. Previous research has found that a number of areas of the brain, including the mPFC and the PCC actually show heightened levels of activity when a person is simply at rest and show decreased activity when concentrating attention on various tasks unrelated to thinking about oneself (D'Argembeau et al., 2005; Wicker, et al., 2003). So while it is true that these brain areas are important for self-awareness, simple tasks such as looking out a window or thinking about another person can reduce activity in these areas under normal circumstances. In the Carhart-Harris et al. study brain activity under psilocybin was compared to brain activity when simply resting. This is potentially a problem because activity in the mPFC and PCC tends to be highest when at rest. Therefore, reduced activity in these regions under psilocybin might simply be because volunteers were paying attention to the unfolding hallucinatory experience as opposed to thinking of nothing in particular. Future studies could test this by using a comparison condition where participants were engaged in an attentional task as opposed to simply resting. If there were noticeable differences in the degree of deactivation in the key brain areas this might provide evidence that these particular brain areas do play a special role in the psilocybin experience.

In spite of these concerns, I do think the idea that psilocybin permits an “unconstrained style of cognition” is an intriguing one. As discussed in my previous article there is a strong association between the personality trait absorption and the degree to which a person experiences alterations in consciousness under psilocybin (Studerus, Gamma, Kometer, & Vollenweider, 2012). Absorption is associated with a tendency to have unusual ideas and loose associations, suggesting that high absorption is associated with a style of cognition that is much less constrained than that of the average person. Additionally, one study of volunteers who had never taken psychedelic drugs before found that volunteers who experienced a profound mystical experience under psilocybin underwent a long-term increase in openness to experience (MacLean, Johnson, & Griffiths, 2011), a personality trait closely related to absorption. This suggests that for some people, taking psilocybin could lead to a lasting change in their cognitive style, perhaps related to the intensely “unconstrained” style experienced under psilocybin.

The study of the effects of psilocybin on brain function is in its infancy. More research into this area could lead to some intriguing findings about the relationship between the brain and consciousness.

Further reading

Another critique of the Carhart-Harris et al. study can be found here.

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© Scott McGreal. Please do not reproduce without permission. Brief excerpts may be quoted as long as a link to the original article is provided.

Other posts about psychedelic drugs and/or spirituality

Psilocybin and personality

Psilocybin for anxiety and depression in cancer

Can the Experience of Awe Open the Mind?

DMT, aliens and reality – part 1

DMT, aliens and reality – part 2

DMT: Gateway to Reality, Fantasy or What?

The Spirituality of Psychedelic Drug Users

Troubled Souls: Spirituality as a Mental Health Hazard

Peak Experiences in Psilocybin Users - Users who trip without drugs

LSD, Suggestibility, and Personality Change


Carhart-Harris, R. L., Erritzoe, D., Williams, T., Stone, J. M., Reed, L. J., Colasanti, A., . . . Nutt, D. J. (2012). Neural correlates of the psychedelic state as determined by fMRI studies with psilocybin. Proceedings of the National Academy of Sciences. doi: 10.1073/pnas.1119598109

D'Argembeau, A., Collette, F., Van der Linden, M., Laureys, S., Del Fiore, G., Degueldre, C., . . . Salmon, E. (2005). Self-referential reflective activity and its relationship with rest: a PET study. NeuroImage, 25(2), 616-624. doi: 10.1016/j.neuroimage.2004.11.048

MacLean, K. A., Johnson, M. W., & Griffiths, R. R. (2011). Mystical Experiences Occasioned by the Hallucinogen Psilocybin Lead to Increases in the Personality Domain of Openness. Journal of Psychopharmacology. doi: 10.1177/0269881111420188

Studerus, E., Gamma, A., Kometer, M., & Vollenweider, F. X. (2012). Prediction of Psilocybin Response in Healthy Volunteers. PLoS ONE, 7(2), e30800. doi: 10.1371/journal.pone.0030800

Wicker, B., Ruby, P., Royet, J.-P., & Fonlupt, P. (2003). A relation between rest and the self in the brain? Brain Research Reviews, 43(2), 224-230. doi: 10.1016/j.brainresrev.2003.08.003

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