What exactly goes on in the brain when one is on a high? What causes the heightened sensory perceptions that one experiences after a drug trip?

A new study published in Human Brain Mapping examined the psychedelic effects magic mushrooms had on the brain, and found that the brain shows the same pattern of activity while consuming drugs that it does while dreaming. Magic mushrooms contain the hallucinogenic compound psilocybin. The effects of the drug include enhanced aesthetic responses such as heightened awareness of colors, textures, contours, and even sounds. It often enables users to have dream-like states.

To understand the brain activity during this experience, researchers injected 15 volunteers with psilocybin and analyzed their brain activity through functional magnetic resonance imaging (fMRI). Their brain activity was also measured when injected with a placebo. It was found that under the influence of psilocybin, activity in the more primitive brain network linked to emotional thinking became more pronounced, with several different areas in this network — such as the hippocampus and anterior cingulate cortex — active at the same time.

This similar activity occurs in the brain when we are dreaming. Conversely, volunteers who had taken psilocybin had more disjointed and uncoordinated activity in the brain network that is linked to high-level thinking, including self-consciousness.

"What we have done in this research is begin to identify the biological basis of the reported mind expansion associated with psychedelic drugs," said Dr. Robin Carhart-Harris from the Department of Medicine, 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."

The research mainly used blood-oxygen level dependent (BOLD) fMRI to map the cerebral blood flow changes that are linked to the activity in the brain. This revealed that psilocybin greatly affected the activity in important brain networks linked to high-level thinking in humans, making it unsynchronized and disorganized. One particular network that was especially affected plays a central role in the brain, essentially "holding it all together" and it's linked to our sense of self. 

In contrast, the more primitive parts of the brain, such as areas of the hippocampus associated with memory and emotion, and the anterior cingulate cortex, which is related to states of arousal, became more co-ordinated under the influence of the drug. 

"A good way to understand how the brain works is to perturb the system in a marked and novel way. Psychedelic drugs do precisely this and so are powerful tools for exploring what happens in the brain when consciousness is profoundly altered," said lead author Dr. Enzo Tagliazucchi from Goethe University, Germany, in a press release. "It is the first time we have used these methods to look at brain imaging data, and it has given some fascinating insight into how psychedelic drugs expand the mind. It really provides a window through which to study the doors of perception." 

Dr. Carhart-Harris added, "Learning about the mechanisms that underlie what happens under the influence of psychedelic drugs can also help to understand their possible uses. 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 1950's and 1960's 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."

The current research was built upon previous studies conducted by Carhart-Harris and his team. To further analyze the changes in brain activity associated with the intake of the drug, the team made use of mathematical models of brain networks.

These models made use of the concept called entropy, a tool that provides a quantitative index of a dynamic system's randomness or disorder and often used to assess brain states and functions. When applied to the context of the brain, increased entropy suggests increased uncertainty or puzzlement.

In this study, researchers found that in the psychedelic state there was a remarkable increase in the entropy in primitive areas, which suggests increased activity in these areas under the influence of psilocybin.

Previous researchers have put forth the theory of "self-organized criticality," which refers to the changes that occur in a complex system when an external input of energy forces the system away from its equilibrium. Every complex system, including our brain, has a critical point, which is the relatively narrow transition zone between the two extremes of order and chaos.

In the brain, this critical point is maintained by a fixed number of dynamic networks. These networks maintain the equilibrium between the stability and flexibility of consciousness. If the number of networks goes above the critical point, the brain enters into a chaotic state. Psilocybin can manipulate this critical operating point, according to the researchers.

Source: Tagliazucchi E et al. 'Enhanced repertoire of brain dynamical states during the psychedelic experience' Human Brain Mapping. 2014.