We think the world activates our brain to create experience but recent research into psychedelics suggests the reverse is sometimes true. External stimuli can mute brain activity. The brain is busy filtering reality when faced with the world. Take the world away, and the brain can go to new and exciting places, writes Pedro Mediano.
Most scientists seek to understand the world around us. Other scientists, like myself, seek to explain the world within us – the elusive nature of the human mind, the physical basis of consciousness, and the seemingly impenetrable barrier between external reality and first-person experience. Therefore, as consciousness neuroscientists, our task is to elucidate how our consciousness is altered in response to changes in our brain and our environment. And there is no alteration quite as powerful and encompassing as that elicited by psychedelic substances.
In the realm of neuroscience, the study of psychedelics has long been a captivating yet enigmatic pursuit. It is only recently that research has started illuminating the intricate relationship between psychedelics, consciousness, and brain activity, revealing a fascinating interplay that extends beyond mere simple hallucinations and the geometric patterns that are commonly associated with these substances. Adding another layer of complexity, we must also take into account the contextual backdrop against which these experiences unfold – how we feel, where we are, and what’s around us – elements collectively called ‘set and setting’. All these factors make up a formidable research endeavour, with deep philosophical implications and convoluted technical challenges. How the outside world shapes inner experience not only informs how we can use set and setting therapeutically – it can also tell us about what that experience is and how it works.
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A rich and diverse inner life, with many different contents springing in and out of consciousness, must be generated by equally diverse activity in the brain, through the interplay of complex patterns of neural activity.
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One of the tools that scientists are using to find signal in the noise is the concept of entropy – a mathematical construct, derived independently in both physics and computer science, that measures the amount of ‘disorder’ in a system. In neuroscience, entropy measures the complexity or ‘signal diversity’ of neural activity, i.e. the number of different patterns in which neurons in your brain activate and send messages to one another. Most of us in fact use this concept of entropy in our daily life, every time we compress a computer file. An image that shrinks greatly in size when compressed does so because it has low visual diversity and a lower entropy, whereas a more visually diverse image would harder to compress, requiring more information to describe it truthfully.
A simple yet powerful account of the relationship between brain entropy and consciousness was put forward in Carhart-Harris’ influential Entropic Brain Hypothesis (Carhart-Harris et al., 2014). This hypothesis stems from a very simple intuition: that a rich and diverse inner life, with many different contents springing in and out of consciousness, must be generated by equally diverse activity in the brain, through the interplay of complex patterns of neural activity. Accordingly, a wealth of studies have shown dramatically increased brain entropy under psychedelics, to the extent that this entropy increase has become one of the most distinctive features of psychedelic neuroscience. ‘Distinctive’ is used here deliberately, rather than ‘unique’, as there are other known examples of increased entropy in the brain, such as states of deep meditation and states of ‘flow’ associated with musical improvisation.
Of the many studies linking entropy and psychedelics, very few of them have taken the importance of context – or ‘setting’ – with the rigour it deserves. To fill this gap, myself and a group of colleagues from across the UK and New Zealand set out to quantify the interplay between the neural effects of setting and the psychedelic substance lysergic acid diethylamide (LSD), in a study published recently in the journal Chemical Neuroscience.
Central to this investigation was the pivotal role of context – the environmental milieu in which the psychedelic voyage unfolds. Recognizing the profound impact of context on subjective experience, the study explores how variations in external stimuli shape the psychedelic journey. The settings ranged from inward-focused, eyes-closed introspection, to serene melodies of ambient music, to the captivating allure of vast natural landscapes in video scenes. Study participants had their brains scanned with a technique called ‘magnetoencephalography’, and we calculated the entropy of their brain activity by (quite literally) compressing the files that came out of the scanner.
The study found that, in the absence of the drug (when subjects received a placebo), there is a direct link between the entropy of brain activity and the entropy of external stimuli: the more complex the environment is, the more complex the brain’s response becomes. This form of ‘complexity matching’ between the brain and its environment already shows that our brains are finely attuned to the richness of the world around us. When participants were under the influence of LSD, as expected, brain entropy surged dramatically in response to the psychedelic compound.
More surprising, perhaps, is the synergistic relationship between psychedelics and context: as the environment became more complex, the entropy-inducing effects of LSD actually decreased. In other words, the effects of LSD on brain entropy were much larger when participants were in an introspective, eyes-closed state, than when they were watching a movie.
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As external stimuli fight for attention, the internal landscapes of LSD-induced imagery recede into the background, overshadowed by the sensory bombardment from the outside world.
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Although the dust is yet to settle and more studies are needed, one can speculate on what neural and mental processes may be responsible for this unexpected result. One tempting interpretation is that brain entropy moves in a subtle dance – a delicate interplay between external and internal worlds. As external stimuli fight for attention, the internal landscapes of LSD-induced imagery recede into the background, overshadowed by the sensory bombardment from the outside world. This tug-of-war between the hallucinations conjured by the drug and the sensory input from the environment paints a picture of the brain grappling with conflicting signals, struggling to maintain coherence amidst the chaos. Moving forward, we hope to elucidate precisely what these results mean for the future of the entropic brain hypothesis: are there different ‘kinds’ of entropy in the brain? How can we measure them? And what do they mean for consciousness?
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More fundamentally, this study is one of a growing list of findings that call into question some of our deeply ingrained views about consciousness. We tend to believe consciousness is purely intrinsic – generated in our brain, by and for ourselves, siloed from the external world. These results, like others before, show that this is simply not the case: our minds are inextricably tied to our bodies and the environment around us, in a complex and fascinating interplay. Your brain, in a sense, ‘filters’ the world around you in synergistic combination with your memories, emotions, and expectations. Two people might see the same thing yet have completely different experiences, since their perception of the world is unavoidably shaped by their brain’s unique dynamics. Psychedelics cause such dramatic alterations of conscious experiences by altering this filter in ways we are yet to fully understand.
Beyond the scientific study of consciousness, in the realm of healing and introspection, a fascinating frontier has emerged where the mystical meets the therapeutic: the world of psychedelic-assisted psychotherapy. When used in a therapeutic setting, the entropic effect of psychedelics opens a window of opportunity when ingrained negative beliefs can be uprooted, shaken, and reformed to give individuals control of their own mind.
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Multiple studies have linked brain entropy during the psychedelic experience with changes in psychological attitudes after the ‘trip’ – opening the door to quantitative approaches to psychedelic psychotherapy.
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The results of this study add another small piece to this daunting puzzle that neuroscientists and psychotherapists are trying to solve. Thanks to these new links between setting and the brain’s response to psychedelics, therapists will be better able to tailor experiences for individuals based on their specific needs. By manipulating context, be it choosing music or allowing time for introspection, we can now make more informed decisions to guide individuals in their own journey.Although the search for the underlying therapeutic mechanisms of psychedelics is still on, multiple studies have linked brain entropy during the psychedelic experience with changes in psychological attitudes after the ‘trip’ – opening the door to quantitative approaches to psychedelic psychotherapy.
As promising as it is, psychedelic psychotherapy is still undergoing clinical trials across the globe, and many questions must be answered before we can use it confidently.
As we delve deeper into the world of psychedelic therapy, we're discovering new ways to support individuals on their journey towards healing and self-discovery. By integrating insights from neuroscience, we're paving the way for innovative approaches to mental healthcare that offer hope and healing to those in need while shedding new light on the deep mysteries of consciousness.
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