The Entropic Brain: The Neuroscience of Psychedelic States
In recent years there has been an explosion in the number of experiments on psychedelics, with hundreds of brain scans done on tripping participants—all in the name of science.
While humans have always been able to experience what happens inside the mind after consuming psychedelic plants and fungi, thanks to these experiments we can finally say what is going on inside the brain. Much of this work has taken place at Imperial College in London, under the supervision of Dr. Robin Carhart-Harris. Based on that work, he has constructed a theory of how psychedelic states in the mind relate to activity in the brain: the entropic brain hypothesis.
The brain is a complex, networked system. A network consists of a group of nodes that connect to each other—think of the connections between individuals that form your social network, or the connections between computers and phones that make up the internet. Much of the intelligence of the brain comes from its being a network. This network consists of more connections than there are stars in the known universe. Rather than relying on individual brain cells to perform specialized tasks, the brain funnels vast amounts of information through your senses into its networked structure, with the complexity of the interactions giving rise to intelligent behavior and our perception of the world around us. Modern breakthroughs in AI are all based on the realization of the vast power of networks to process information. Networks are inherently complex. You can’t just study the components; you have to consider layer after layer of interactions. Despite the challenge to our understanding, the power lies in this complexity.
Therefore, we need to understand the complexity itself. Complex systems show novel behavior when the components of the system interact. That is, the whole is greater than the sum of the parts. In a complex system, new features emerge that can’t be explained by reducing the system to its parts. Think of the way that water and temperature interact in our climate to produce clouds, rain, and snow. Considering individual water molecules separately will never give you an explanation for these features of our weather. You have to consider the complex interactions. That can be daunting! It’s much easier to think in reductionist terms. But when it comes to understanding systems like the climate or the brain, it’s what we have to do. Fortunately, there is structure in complexity.
There are some useful concepts we can use to make sense of these vast amounts of interactions. One such concept is the entropy of the system. Entropy is a term that comes from thermodynamics, roughly corresponding to the disorder of a system. A system that is too highly ordered isn’t of much use. If every brain cell were to turn on and off at the same time, it would be highly ordered. In that case, you may as well have one brain cell, as all the rest would be redundant. The power of the system seems to come from the fact that there’s some level of entropy in it.
The system has some level of disorder that makes it possible for interesting things to happen. It’s easy to see how this could be overdone, however. Have complete chaos with every neuron doing its own thing and you’d most likely struggle to keep your heart pumping.
There must be a “sweet spot” in the middle where the interesting dynamics that underpin intelligence and perception emerge. Let’s call this sweet spot a “Goldilocks zone” of the brain and the mind. This is the core of the entropic brain hypothesis: It draws a link between the states of the brain and the states of the mind. It holds that the entropy of brain states is directly related to the richness of mental experience. Before our consciousness develops the familiar, stable character that allows you to read these words, our experience as infants is thought to resemble the psychedelic state. This “primary state” of consciousness is richer than adult waking consciousness and, according to the entropic brain hypothesis, would be characterized by greater entropy in the spontaneous activity of the brain.
The prediction is that psychedelics alter consciousness by increasing the entropy of brain activity.
They move the mind into a primary state of greater experiential richness. Why do we develop out of these primary states, always experiencing the world with the richness of a trip? The answer may be obvious. Consider how you would successfully go about your day if that were the case. Our brains are fundamentally survival machines, crafted by evolution to help us survive with as little energy as possible.
The more you can perform tasks habitually, the more energy you can save physiologically and mentally.
The richness of a trip may be enjoyable for a few hours—but not ideal on the morning commute. We’re constantly developing the routine habits we need to easily navigate the world. As we do so, we lay down physical pathways in the brain that reduce the range of possible states the brain can be in, increasing its order, reducing its entropy—and reducing the richness of experience. For many, however, this order can go too far. We can get trapped in repetitive, depressive thought patterns. We can anxiously ruminate over things that are out of our control. In the framework of the entropic brain hypothesis, people might benefit from an increase in brain entropy, courtesy of a psychedelic. This increase in the entropy of spontaneous brain activity may be a core mechanism that allows psychedelics to be so powerful in treating a range of mental health disorders. However, some disorders, such as schizophrenia, may already involve excessive entropy in brain states. This may account for why psychedelics are not recommended for people at risk of psychosis. What is so special about the psychedelic state? In addition to freeing the brain and mind from oppressive habitual patterns, psychedelics may move the brain into a particularly interesting point on the spectrum from chaos to order. This is where another useful concept in making sense of complexity comes in: criticality. Nature is full of complexity. How do large-scale complex phenomena like trees evolve from small interacting elements? Patterns in nature often have a fractal structure, with the patterns at the large scale resembling the patterns at the small scale. Think of how the veins of a leaf resemble the branching structure of the tree as a whole. It doesn’t matter at what scale you look; the same patterns are there. It turns out this is a powerful way for complexity to emerge out of simple interactions. If you pour sand, it usually forms a pile in the shape of a cone.
The arrangement of the grains at the small scale produces a similar arrangement at the large scale. If you add a few new grains, they can trigger large-scale avalanches down the side of the pile.
The pattern of tumbling of the small grains mirrors the collective pattern of the whole avalanche. At this critical point between chaos and order, complex systems emerge.
The behaviour of the whole is robustly coupled to the behaviour of the small components. When the brain is poised at this point of criticality, small changes in the activity of certain brain areas can trigger avalanches of associations. We can use the idea of psychedelics increasing criticality to make sense of the importance of set and setting to the character of a psychedelic trip. A situation that is anxiety-producing can result in a mental avalanche of associated thoughts. This can lead to panic, or at least a challenging experience. On the positive side, however, an increase in criticality can lead to the unearthing of long-forgotten memories and the production of new insights.
The brain in this state is freed from its old habits. It can effortlessly explore whole new ways of being, and whole new ways of perceiving the world. This newfound flexibility and freedom may be exactly what people stuck in the ruminative patterns of depression and anxiety need. Brain imaging studies of individuals undergoing a psychedelic trip have validated the framework of the entropic brain hypothesis. Functional magnetic resonance imaging (fMRI) studies of people who have taken LSD show increased entropy and criticality of spontaneous brain activity. This is exactly what these experiments predicted.
The entropic brain hypothesis offers a framework for thinking about how brain states relate to mental states. We can apply it to child development, a variety of mental health issues, and comparisons between normal waking consciousness and the psychedelic state. What’s more, it’s a tool for furthering our thinking about how consciousness relates to the brain. For a long time the word “entropy” was largely confined to physics departments in universities. In years to come perhaps we will all watch our brain entropy in the way we watch our weight, as another way of empowering us to live healthier lives.
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