When neuroscientist Dr Robin Carhartt-Harris and his team wanted to study the effects of Psilocybin mushrooms, a type of psychoactive fungi, on the brain, his initial hypothesis was that the psychedelic experience produced would increase cerebral blood flow. They predicted that, in an fMRI scanner, this would show up as increased oxygen levels across the brain. They noticed, however, that there was a significant decrease in oxygen level concentrated around one specific brain structure, the default mode network.

The default mode network (also known as the DMN) was discovered in 2001 by neurologist Marcus Raichle. When Raichle was studying volunteers in an fMRI scanner, he noticed that when they were waiting in the scanner to take part in a test, several parts of the brain showed heightened activity. This was the brains ‘default mode’ and this network of structures light up when the brain has no task to perform. In other words, the DMN is where our minds go to daydream, self reflect and worry.

The DMN also plays a key role in creating mental constructs. One of these constructs is what psychologist Sigmund Freud called the ‘ego’, and which some neuroscientists call “the me network”. The ego is a mental mechanism that the mind creates to distinguish the ‘I’ as a separate entity from ‘them’ and ‘that’. It is the ego which is concerned with how we are viewed and how we form our identity based on our experiences. This is why the DMN lights up when we get ‘likes’ on social media and when we go back into our autobiographical memory.

Philosopher Aldous Huxley believed that when it comes to our perception of reality, the ego acts as a filter. This is so that we use energy resourcefully and so that our brains do not process everything that is received from the world. While we may believe that we view the world in its totality, Huxley suggested that we only percieve part of reality. This is because the ego acts like a ‘reducing valve’ which only lets in the information we need to survive.

This is also the reason why human consciousness is so different from the consciousness of other animals. For example, while we can see specific colours, bees can perceive electrical signals from plant petals, and they can distinguish between different signals like we do colours. The human brain and bee brain differs in what it is conscious of and neither is fully conscious of all that is out there. Because of this reducing valve, our everyday awareness is an inhibited version of full awareness.

The evolution of the ego was a great evolutionary step as it allowed humans to focus on the advancement of the self. This is because the ego is only concerned with being conscious of that which is needed for getting ahead, getting food and reproducing. But this mechanism also comes with some drawbacks. As the ego distinguishes our self from others and the world, it separates us from everything external from us, leading to a sense of isolation.

“A human being is part of the whole called the ‘Universe’, a part in time and space. he experiences himself, his thoughts and feeling as something separated from the rest – a kind of optical delusion of his consciousness. This delusion is a kind of prison for us.” Albert Einstein, The Einstein Papers: A Man of Many Parts

Furthermore, if the DMN is faulty it can lead to excessive self-reflecting and worrying, and the ego’s rigid filter will hinder the mind from opening up to more than its current thoughts. This inevitably leads to destructive behaviours. Studies similar to the one conducted by Dr Robin Carhartt-Harris show that once consumed, psychedelics dis-inhibit the reducing valve of the ego and quieten the DMN. The psychedelic experience loosens the filter and frees the mind to enter other realms of consciousness. It allows the mind to create new thoughts.

Carhartt-Harris theorised that some psychological disorders were the result of excessive order in the mind and not a lack of order. He suggested that when the DMN settles into the same rigid patterns of thought, the mind is unable to create new mental states and ways of thinking. Research has shown that a hyperactive DMN causes individuals to be trapped in repetitive and destructive loops of self-reflection which eventually shut the person off from the outside world. Disorders such as depression, obsessive-compulsive disorder (OCD) and addiction are characterised by excessively rigid patterns of thought.

Psychedelics have been shown to disrupt these patterns. The exact way they do this is uncertain but research points to their neurochemical effects on the brain. Psychedelic compounds bind to serotonin receptors causing neurons to fire in a certain way. This firing of new signals disrupts the usual oscillations of the DMN. One way to imagine this if you think of an audience clapping in the same rhythm. If there a few people who produce some wayward claps, the entire rhythm will desynchronise to chaos.

Once these patterns are disrupted, the mind is then free to create new possibilities. In the picture above is a simplified model of the number of neurological connections in the brain between a non-active placebo (left) and psilocybin (right). As we age, the filtering of our perception becomes habit and consequently, our brains become efficient machines in dealing with life’s everyday situations. This causes the neural connections in our brain to act automatically as these connections become ingrained. This is what the image on the left is showing. The image on the right shows all the new connections the mind makes when on a psychedelic.

Studies show that the psychedelic experience has profound effects on those with addiction issues particular. In one study, 80% of addicted smokers who were given psilocybin achieved cessation of their habit, a rate that has yet to be achieved by other smoking cessation treatments. Other studies showed that after psychedelic experiences, addicts admitted a sense of awe at being connected to the world and others and because of this, recognised the harm that they were doing.

“Psychedelics would be for psychiatry what the microscope is for biology and the telescope is for astronomy.” Dr. Stanislav Grof

While the use of psychedelics are a potential way to ease suffering for the unwell, they may be equally useful for the well. In studies where healthy people were given a psychedelic, many described their experience as mystical. The mystical experience is represented by many factors which include a sense of awe, attainment of insightful knowledge and the fusion of the personal self into a larger whole. After these experiences, people come away feeling more grateful for being alive, they implement what they’ve learned to make changes in their behaviour and they feel that they’re not a small separate entity in the universe but that they’re part of it. They escaped their prison of perception and now have new meaning in their life.