The foremost physiological effect of psychedelics in the brain is to significantly reduce activity in multiple brain areas, which contradicts the mainstream reductionist expectation. Physicalist neuroscientists have proposed that an increase in brain noise explains the subjective richness of a psychedelic experience, but a psychedelic experience isn’t akin to TV static, argues Bernardo Kastrup.

Before 2012, the generally accepted wisdom in neuroscience was that psychedelic substances—which lead to unfathomably rich experiential states—stimulate neuronal activity and light up the brain like a Christmas tree. Modern neuroimaging, however, now shows that they do precisely the opposite: the foremost physiological effect of psychedelics in the brain is to significantly reduce activity in multiple brain areas, while increasing it nowhere in the brain beyond measurement error. This has been consistently demonstrated for multiple psychedelic substances (psilocybin, LSD, DMT), with the use of multiple neuroimaging technologies (EEG, MEG, fMRI), and by a variety of different research groups (in Switzerland, Brazil, the United Kingdom, etc.). Neuroscientist Prof. Edward F. Kelly and I published an essay on Scientific American providing an overview of, and references to, many of these studies.

These results contradict the mainstream metaphysics of physicalism for obvious reasons: experience is supposed to be generated by metabolic neuronal activity. A dead person with no metabolism experiences nothing because their brain has no activity. A living person does because their brain does have metabolic activity—or so the story goes. And since neuronal activity supposedly causes experiences, there can be nothing to experience but what can be traced back to patterns of neuronal activity (otherwise, one would have to speak of disembodied experience). Ergo, richer, more intense experience—such as the psychedelic state—should be accompanied by increased activity somewhere in the brain; for it is this increase that supposedly causes the increased richness and intensity of the experience.

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Since brain activity doesn’t increase in the psychedelic state, physicalist neuroscientists then conclude that something else in the brain must.

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Notice that physicalism would remain consistent with an overall decrease of brain activity in the psychedelic state, provided that one could still find localized increases in parts of the brain consistent with the experience. The reason for this is that, under physicalism, not all neuronal processes lead to experience; only the so-called ‘Neural Correlates of Consciousness’ (NCCs) supposedly do. It is thus conceivable that psychedelics could reduce activity in processes not related to conscious experience, while leading to localized increases in the NCCs. In particular, it is conceivable that psychedelics could impair inhibitory processes that, once impaired, disinhibit the NCCs. The problem is that all this relies on there being plausibly sufficient increases of activity somewhere in the brain—corresponding to the now-disinhibited NCCs—compared to the baseline, so as to account for the increase in the richness and intensity of experience. But no such a thing has been seen.

Since brain activity doesn’t increase in the psychedelic state, physicalist neuroscientists then conclude that something else in the brain must. And so the hunt is on for something in the brain that increases under the effect of psychedelics. Many possibilities have been proposed and somewhat fallen by the wayside, such as brain activity variability and functional connectivity. But one remains and is significantly hyped as the best physicalist hypothesis for accounting for the psychedelic experience. It goes by various names, such as ‘brain entropy,’ ‘complexity,’ ‘diversity,’ and so on. But what it means is very straightforward: brain noise—i.e., residual brain activity that unfolds according to no discernible pattern; brain ‘TV static,’ if you like.

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The idea here is that, although brain activity decreases with psychedelics, the residual activity that remains is desynchronized by the drug, thereby becoming relatively more random than in the baseline. And this relative increase in randomness or entropy—the latter meaning the degree of disorder of the remaining brain activity—is supposed to account for the unfathomable experiential immensity of the psychedelic state. The logic is that more random activity contains more Information than synchronized activity with discernible patterns. Under a certain definition of ‘Information,’ which I shall elucidate below, this is indeed true. And thus, the extra Information physiologically imparted by psychedelics supposedly accounts for the extra richness and intensity of the psychedelic experience.

There are many reasons why this ‘entropic brain hypothesis’ is implausible to be point of being bizarre, so let’s tackle them systematically, starting with the underlying logic discussed above. The fallacy of trying to account for richer, more intense experience in terms of higher Information content is that it relies on conflating two completely different definitions of the word ‘information.’

The first definition was that coined by Claude Shannon, father of information theory, in his seminal 1948 paper, ‘A Mathematical Theory of Communication.’ The idea there is that Information is a measure of the level of ‘surprise’ embedded in a message or signal. More specifically, the more alternative possibilities are eliminated by a message or signal, the more ‘surprise value’—and, therefore, Information—it contains. For example, if a message stated simply that a certain person is married, then only one other possibility would be eliminated: namely, that the person is single. The level of ‘surprise’ here is only 50%, since only one out of two possibilities can be eliminated by the message. But if a message were to contain, say, a picture of the cloud cover over your city, countless other possible patterns of cloud cover would be eliminated by it, and the level of ‘surprise’ would be much greater. That picture would thus contain a lot more Information.

One way to operationalize this particular definition of Information is to think in terms of compression. A photograph—playing the role of message, or signal—with clear and repeated visual patterns is compressible and can, therefore, be stored in a smaller computer file. The discernible patterns allow the compression algorithm to discard many pixels from the original image, since the algorithm can later reconstruct those pixels based on knowledge of the patterns according to which they appeared in the first place. For example, a photograph of an empty chessboard is highly compressible, because the black and white pixels appear on it according to a very regular pattern, so there is no need to store each and every pixel; all we need is to know the pattern of a chessboard. But a photograph of TV static is much less compressible, for the black and white pixels do not follow any recognizable pattern. In this latter case, nearly all pixels need to be stored.

Shannon’s definition of Information means that, the more compressible a signal is, the less Information it has, for knowledge of the associated patterns reduces the degree of ‘surprise’ we have when we analyze the signal. By the same token, the less compressible a signal is, the more Information it contains, for our inability to recognize underlying patterns renders many ‘pixels’ in it unexpected and, therefore, ‘surprising.’ When I use the word ‘Information’ in Shannon’s sense, I capitalize it, as I have already been doing.

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Now, Shannon’s definition of ‘Information’ is a very technical one, invented for very specific purposes in communications engineering. It doesn’t—and was never meant to—replace the colloquial use of the word. In the colloquial sense, the word ‘information’ (this time not capitalized) means the amount of semantic content of a message or signal. This way, a message or signal has a lot of information if it means a lot. On the other hand, a message that means nothing has no information.

The crucial thing to notice here is that, in a very important sense, Information and information are opposites. A completely random and uncompressible signal has maximum Information, but no information; for a random signal means nothing: it has no discernible structures or patterns that could be recognized and therefore unlock cognitive associations. TV static has near-maximum Shannon Information, but it means nothing. Therefore, it has no information in the colloquial sense, this being the reason why we don’t sit in the living room to watch TV static; instead, we watch TV programs, which have a lot of recognizable—and, therefore, compressible—patterns in the form of objects, people, and events. As such, a signal with a lot of information has, by definition, lots of recognizable patterns, therein residing its meaning. Yet—and precisely for this reason—it has relatively little Information in Shannon’s sense.

When claiming that psychedelics increase the amount of Information in the brain, the proponents of the ‘entropic brain hypothesis’ are using Shannon’s technical definition of Information. But when claiming that an increase in the information content of the brain accounts for the richness and intensity of the psychedelic experience, they can only be appealing to the colloquial definition of information. Alas, these two denotations not only aren’t the same, they effectively are opposites. The proponents’ conflation of the different meanings of the word ‘information’ renders their entire logic nonsensical. They seem to stick to the mere word without understanding what it means in different contexts. The intuitive appeal of their hypothesis is thus no more than a linguistic phantasm; and a rather superficial one at that.

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After all, a psychedelic experience isn’t random or unstructured; it isn’t akin to TV static.

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When a subject describes a psychedelic experience as rich and intense, what the subject means is that the experience has a lot of semantic content; i.e., it means a lot to the subject, unlocking many associative links in a cognitive chain reaction. This richness of meaning is evoked by recognizable cognitive structures and patterns, which is the opposite of entropy. After all, a psychedelic experience isn’t random or unstructured; it isn’t akin to TV static. If it were, it precisely wouldn’t be described as rich or intense, but mind-numbingly boring instead; for there is nothing more devoid of evocative semantic content than TV static. A psychedelic ‘trip’ is so unfathomably rich and intense precisely because it has relatively little Shannon Information, and a whole lot of information in the colloquial sense. Random, entropic brain activity is thus precisely the opposite of what one would expect under physicalist premises; provided, of course, that one actually understands information theory. Just about anything else would be less implausible a physicalist account of the psychedelic experience.

Now, even if we ignore the entire discussion above, and pretend, for the sake of argument, that Information and information are the same thing, the ‘entropic brain hypothesis’ still has no legs for obvious other reasons. I’ve discussed this ad nauseum in previous writings, so I shall limit myself to a mere summary here.

Decades of research in the neuroscience of consciousness have demonstrated consistent correlations between patterns of brain activity and reported inner experience. Under physicalism, this suggests that the only plausible account of experience is brain activity. But if the ‘entropic brain hypothesis’ were correct, it would imply that, in the case of psychedelics alone, something totally else must account for experience. What is the likelihood that there are two completely different brain mechanisms that generate experience under physicalist premises? One cannot defend physicalism by proposing a completely different theory of consciousness for each different set of data, as this would be grotesquely inflationary and render physicalism unfalsifiable to the point of being meaningless.

Moreover, the increase in brain noise—pompously called ‘complexity’ or ‘diversity’ by the proponents, which misleads casual readers into concluding that psychedelics induce more ‘complex’ or ‘diverse’ brain activity, in the colloquial sense—measured during the psychedelic state is ludicrously minute: it averages at 0.005 in a scale that runs from 0 to 100! The proponents’ defense here is that, minute as it is, the effect is still statistically significant. But this misses the point entirely: statistical significance only means that the effect isn’t a measurement or methodological artifact; it says precisely nothing about the strength of the effect. And the strength of the effect is key, for the proponents are trying to account for the mind-boggling richness and intensity of the psychedelic experience—a very, very large subjective effect—in terms of a ludicrously minute physiological effect. This stretches plausibility.

Indeed, it seems silly to suggest that a 0.005% increase in brain noise, of all things, accounts for life-changing, imaginary trips to other dimensions, conversations with aliens, insights into the fabric of reality, the nature of the self, life, the universe, and everything. Imaginary and illusory as they may be, these experiences are real as such; i.e., as experiences. And so they must be accounted for, under physicalism, in terms of plausibly comparable physiological effects. Short of an appeal to magic, a minute increase in brain noise just isn’t one such a physiological effect.

Finally, the brain noise increase observed during the psychedelic state is a statistical average. For some of the placebo-drug pairs studied, brain noise went the other way: it decreased. Yet, those subjects also had the psychedelic experience. What, then, accounts for their experiences under physicalist premises?

Analytic idealism accommodates all these empirical observations without the problems and contradictions entailed by mainstream physicalism. Under idealism, the brain and its patterns of neuronal activity are not the cause of inner experience, but the image, the extrinsic appearance of inner experience. In other words, brain activity is what inner experience looks like when observed from the outside. As such, the correlations ordinarily observed between patterns of brain activity and inner experience are due to the trivial fact that the appearance of a phenomenon correlates with the phenomenon. And the break of this correlation observed in the psychedelic state is due to the fact that, unlike a cause, the appearance of a phenomenon doesn’t need to be always complete—i.e., the appearance of a phenomenon doesn’t need to always reveal everything about the phenomenon. For instance, if you were standing right in front of me, facing me, your appearance would not reveal your back, what’s under your skin, the microscopic details of your metabolism, etc.; a great many things would remain hidden, undisclosed by your extrinsic appearance. In just the same way, the appearance of inner experience that we refer to as brain activity isn’t always complete: during the psychedelic state, it leaves out quite a bit about the phenomenon it is an appearance of. And there is nothing extraordinary or counterintuitive about it.

The ‘entropic brain hypothesis’ is a linguistic charade; it is both illogical and empirically inadequate. This leaves mainstream physicalism unsupported as a viable metaphysics of mind.