Neural correlates of the psychedelic

Posted by Simon Raggett on 21 February 2012 | 0 Comments

Tags: Zen meditation, altered states of consciousness, spiritual experience, sensory cortex

A reecent neuroscience paper further undermines the persistent claim within mainstream consciousness that all that needs to be done is to deconstruct the self (a relatively easy process), and then declare the consciousness problem solved. Altered states of consciousness have always appeared to contradict this claim, but the evidence for this tended to be at a rather anecdotal level. Compiled by several prominent universities, this paper demonstrates that it is likley that the self can be deactivated by a drug or other means, while the subject continues to have conscious experiences.

In their paper, the authors use psilocybin, present in so-called 'magic mushrooms', to study the transition from a normal to an altered state of consciousness. Subjects receiving psilocybin were compared to a control group receiving a placebo. The authors were surprised that a markedly altered state correlated with a reduction in blood flow and BOLD signal, rather than their expectation of increased neural activity.

The biggest reductions were observed in the thalamus and the cingulate cortex. The larger the decrease observed, the greater was the reported strength of the subjective experiences. The decreases were localised in associative regions of in hub/connector regions such as the thalamus and parts of the prefrontal. The biggest reductions were observed in the thalamus and the cingulate cortex. In particular, psilocybin caused a large decrease in interaction between the medial prefrontal cortex and the posterior cingulate cortex.

This is taken by the authors to imply that the altered state correlates with decreased connectivity between neural hubs involved in connecting and organising the brain. One possibility suggested is that deactivation in frontal areas such as the posterior cingulate leads to enhanced influence from sensory areas. Presumably it is this which allows an altered perception of the world.

Some theorists have suggested that the posterior cingulate and the associated 'default-mode network' have a role in the experience of the 'self' or self-consciousness. The default network of which  the posterior cingulate is part also involves the largest concentration of cortico-cortical connections in the brain. Deactivation of such connections may relate to alterations in conscious states. This idea is seen by the authors as being consistent with Aldous Huxley's concept of the brain as a reducing valve.

The authors consider the results of their study unexpected, and therefore in need of some explanation. Previous studies had shown an increase in brain activity in terms of glucose metabolism, and there has been an assumed connection between psychedelics and increased neural activity. The authors suggest that stimulation of serotonin transmission by the drug, leading to increases in GABA transmission, could in turn cause the inhibition of pyramidal cells, and the observed deactivation in some brain areas.

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