For the first time, researchers have measured the level of entropy for different networks in the brain under the influence of psilocybin, the psychedelic chemical in magic mushrooms. They found that activity in the more primitive brain network linked to emotional thinking became more pronounced – a pattern of activity similar to that observed in people who are dreaming.
Psychedelic drugs are unique among other psychoactive chemicals in that users often describe “expanded consciousness,” including enhanced associations, vivid imagination and dream-like states. To explore the biological basis for this experience, researchers analyzed brain imaging data from 15 volunteers who were given psilocybin intravenously while they lay in a functional magnetic resonance imaging scanner. Volunteers were scanned under the influence of psilocybin and when they had been injected with a placebo.
“What we have done in this research is begin to identify the biological basis of the reported mind expansion associated with psychedelic drugs,” said researcher Robin Carhart-Harris, from Imperial College London. “I was fascinated to see similarities between the pattern of brain activity in a psychedelic state and the pattern of brain activity during dream sleep, especially as both involve the primitive areas of the brain linked to emotions and memory. People often describe taking psilocybin as producing a dreamlike state and our findings have, for the first time, provided a physical representation for the experience in the brain.”
Carhart-Harris examined variation in the amplitude of fluctuations in what is called the blood-oxygen level dependent signal, which tracks activity levels in the brain. This revealed that activity in important brain networks linked to high-level thinking in humans becomes unsynchronized and disorganized under psilocybin. One particular network that was especially affected plays a central role in the brain, essentially “holding it all together,” and is linked to our sense of self.
Conversely, activity in the different areas of a more primitive brain network became more synchronized under the drug, indicating they were working in a more coordinated, “louder” fashion. The network involves areas of the hippocampus, associated with memory and emotion, and the anterior cingulate cortex which is related to states of arousal.
As part of the new study, published in the journal Human Brain Mapping, the researchers applied a measure called entropy. This was originally developed by physicists to quantify lost energy in mechanical systems, but entropy can also be used to measure the range or randomness of a system. For the first time, researchers computed the level of entropy for different networks in the brain during the psychedelic state.
This revealed a remarkable increase in entropy in the more primitive network, indicating there was an increased number of patterns of activity that were possible under the influence of psilocybin. “It seemed the volunteers had a much larger range of potential brain states that were available to them, which may be the biophysical counterpart of mind expansion reported by users of psychedelic drugs,” said co-researcher Enzo Tagliazucchi, from Goethe University.
Previous research has suggested that there may be an optimal number of dynamic networks active in the brain, neither too many nor too few. This may provide evolutionary advantages in terms of optimizing the balance between the stability and flexibility of consciousness. The mind works best at a critical point when there is a balance between order and disorder and the brain maintains this optimal number of networks. However, when the number goes above this point, the mind tips into a more chaotic regime where there are more networks available than normal. The new findings suggest that psilocybin can manipulate this critical operating point.
“Learning about the mechanisms that underlie what happens under the influence of psychedelic drugs can also help to understand their possible uses,” said Carhart-Harris. “We are currently studying the effect of LSD on creative thinking and we will also be looking at the possibility that psilocybin may help alleviate symptoms of depression by allowing patients to change their rigidly pessimistic patterns of thinking. Psychedelics were used for therapeutic purposes in the 1950s and 1960s but now we are finally beginning to understand their action in the brain and how this can inform how to put them to good use.”
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