- Written by Scott A. McGreal, MSc.
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).