Author: Jordan Hall
Institution: Duke University
Date: March 2012
Magic mushroom users often describe a feeling of having their minds expanded, but a new study reveals that this psychedelic state results from diminished brain activity. A recently published study interpreting functional brain scans of volunteers under the influence of the active psychedelic compound in magic mushrooms, psilocybin, has provided scientists with a new view of how the psychedelic state is achieved in the brain—one that may elucidate how to treat depression and headaches.
“It has been commonly assumed that psychedelic [drugs] work by increasing neural activity,” writes Imperial College London neuro-psychopharmacologist David Nutt, lead author of the study published in the Proceedings of the National Academy of Sciences.
This widely held belief is based on the fact that psychedelia involves a rise in consciousness, which until now scientists thought resulted from increased neuronal activity. These changes in activity from normal brain function are believed to cause the strange sensations and visual hallucinations characteristic of the psychedelic trips commonly reported.
To test this theory, 30 healthy volunteers with previous psychedelic experience were injected with psilobyn and given before and after brain imaging scans. The researchers used two types of functional magnetic resonance imaging (fMRI), which measures brain activity by mapping and monitoring blood flow and oxygen levels in the blood. An increase of blood flow and oxygen concentration is associated with higher levels of activity.
Results showed that while participants subjectively experienced expanded mental capacity, psilocybin actually decreased brain activity. The intensity of the subjective effects reported by participants was directly correlated with decreased blood flow and oxygen concentration in specific areas of the brain.
The areas consistently displaying the largest decrease in activity were the medial prefrontal cortex (mPFC) and the posterior cingulate cortex (PCC).
These are vital “hub” regions of the brain connected to numerous other areas responsible for higher-level cognitive functions, including consciousness and self-identity. Consequently, alterations of activity in these highly-integrated regions may explain why psychedelics acutely affect consciousness.
In addition to identifying the underlying neural mechanism of psilocybin, some therapeutic effects of the compound were also identified.
“The activity of the mPFC is known to be elevated in depression… [and] was consistently deactivated by psilocybin,” Nutt writes. While most ant-depressants do in fact target the mPFC, they do have additional side effects that were not observed with psilocybin. Similarly, psilocybin reduced blood flow in the hypothalamus, a region where blood flow is increased during headaches, perhaps explaining case reports of improved symptoms under psilocybin. The authors note that these additional results need further study before any therapeutic conclusions can be established.
This science news brief was written under the guidance of JYI Science Writing Mentor Jake Berkowitz.