What happens in the brain when you take psychedelics?

Short answer

Certain psychedelic drugs bind to specific sites (serotonin receptors) in the brain, causing them to respond in unusual ways. This, in turn, leads to a complex overload of information in the brain, resulting in an altered state of consciousness. This could help explain typical effects such as the sensation of losing one's sense of self and changes in perception and thought patterns. However, much about the mechanism of psychedelics remains unknown.

Longer answer

Psychedelic drugs like LSD, psilocybin, and DMT can induce hallucinations and temporarily alter consciousness. But before we can understand what occurs in the brain when we take these substances, we must first explore how brain cells usually communicate with each other.

Neurotransmitters and receptors
The brain is made up of billions of cells known as neurons. These neurons continuously send and receive information through electrical signals within the brain and body. Neurons connect to other neurons or muscles through synapses, which are the sites where information transfer takes place. When a neuron receives a signal, it releases a chemical substance called a neurotransmitter, which is then picked up by other neurons. Every neuron has components called receptors that capture neurotransmitters to receive the message. Different types of receptors trigger different responses in the receiving neuron. The neuron processes all incoming messages and responds accordingly, such as instructing the next neuron to act or signalling a muscle to contract or relax. Once the message is received, the sending neuron reabsorbs the neurotransmitter. This cycle repeats every time a new message arrives. In this way, neurotransmitters can be seen as the chemical messengers in our body.

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Serotonin is one such neurotransmitter. Typically, serotonin plays a key role in regulating mood. Some psychedelic substances share a chemical similarity with serotonin. It’s like the difference between a car and a truck: although they are not identical, they are built from the same fundamental components. This similarity allows psychedelics to have a huge impact on the serotonin in the brain. For instance, psychedelics can cause serotonin to interact with different receptors than usual. This often happens in neurons related to vision and attention control, which results in altered messaging between these neurons. This helps explain some psychedelic effects, such as visual hallucinations and disorganised thinking. When larger doses of the drug are taken, more receptors become activated, leading to stronger effects.

Filter
One brain region affected by psychedelics is the thalamus. Normally, the thalamus functions as a filter, preventing the brain from becoming overwhelmed by signals from inside and outside the body. Under the influence of psychedelics, serotonin receptors in areas linked to the thalamus are activated. As a result, the thalamus can no longer carry out its filtering role, causing a sensory overload in the brain. This results in a shift in consciousness often likened to psychosis.

Being in the present
Two other brain areas heavily influenced by psychedelics are the ‘temporal-parietal junction’ and the ‘medial-prefrontal cortex.’ These areas are involved in complex functions like ‘mentalising’ – our ability to understand the mental states of ourselves and others. Furthermore, regions typically active during self-reflection, rumination, and daydreaming become less active during a psychedelic experience. This reduces the focus on the self and allows for more flexible thinking. This is likely why individuals on psychedelics often feel wholly immersed in the sensory experiences the drugs create.

Communication
Psychedelics don’t just change how neurons communicate with one another; they also alter the interactions between brain regions that don’t usually communicate while suppressing communication in areas that normally interact more frequently. Essentially, the brain is ‘shaken up’ during a psychedelic trip, leading to new ways of perceiving life. This opens the door for fresh insights and the potential to break old, unhelpful patterns. For this reason, scientists believe psychedelics could be used in the treatment of psychiatric conditions such as depression, anxiety, or addiction. However, it is important to recognise that psychedelics heavily influence brain activity, so they should only be used under professional supervision, particularly when medical or psychological issues are present.

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