(An improved and updated version of this material has appeared in some of my academic papers. The version below is kept for legacy purposes.)
As regular readers know, I have cited before a very interesting study recently done in the UK on the effects of psilocybin (the active ingredient of magic mushrooms) on the brain. The study caught my attention because preliminary reports suggested that the researchers observed only reductions in brain activity while subjects were having unfathomable psychedelic trips. This, of course, is counter-intuitive: If the hallucinations are not being caused by drug-induced brain activations, where does the trip come from? Now, finally, the complete scientific paper containing the results of the study has been published in the Proceedings of the National Academy of Sciences of the USA. Summaries have also been published in Nature and in Scientific American. Here, I'd like to discuss these results in a little more depth than I did before.
To me, what is of significance in this work is not the psychedelic connection, but the idea that extremely intense subjective experiences can occur without accompanying brain activations; a kind of disembodied experience, if you will, which seems to contradict the currently-accepted notion that the brain generates consciousness. Preliminary reports on this study already indicated that the researchers had observed a reduction of brain activity, but the explanation could have been that the drug selectively affected inhibitory brain processes, thereby allowing excitatory processes to grow unchecked elsewhere. Let me unpack this a bit for you: Inhibitory brain processes are like bouncers guarding the entrance of the club of consciousness. Excitatory brain processes become conscious if they get into the club, but the bouncers prevent many from entering, so we never become aware of them. If the drug takes out the bouncers, the idea is that many excitatory processes that would otherwise remain unconscious now can flood into the club. This would explain the 'trip.'
The problem, having now studied the paper carefully, is that the researchers observed no brain activation anywhere. Quoting the paper: "we observed no increases in cerebral blood flow in any region." You see, if the club of consciousness got flooded because the bouncers were taken out, the researchers should still have seen the increases in blood flow corresponding to the excitatory processes now invading the unguarded club of consciousness. But they didn't. In fact, they observed that the more the drug de-activated the brain, the more intense were the subjective experiences reported by the subjects. This is profoundly anomalous. Subjects reported experiences like "geometric patterns," "extremely vivid imagination," seeing their "surroundings change in unusual ways," as well as experiences with a "dream-like quality." Without brain activations observed anywhere, and with the subjects stuck inside an fMRI scanner, I ask you: Where did all these experiences come from? One would expect, for instance, visions of geometric patterns to be caused by activations of visual areas of the brain. But the researchers not only did not observe these activations, they reported that "there were ... additional ... signal decreases ... in higher-order visual areas." How is this possible? It suggests that the unfathomable experiences of a psychedelic trip are disembodied, occurring somehow outside the brain; a disembodied tripper, if you will.
If you want to have an idea of the kind of structured, coherent, evocative, and unfathomably intense subjective experiences that people have under the effect of psilocybin, I recommend the Erowid experiences vault. If you browse through those reports, you will likely convince yourself that, if consciousness is indeed merely the result of brain activity, it is inconceivable that such experiences could occur without the brain lighting up like a Christmas tree. Yet, the opposite happens; the brain largely goes to sleep. Who, then, is having the trip? It doesn't seem to be the brain.
As I mentioned earlier, I have cited this British study before as a way to substantiate my hypothesis that the brain is a mechanism for localizing and limiting consciousness to a space-time locale, but does not generate consciousness. Surprisingly, the researchers acknowledged this explicitly in the paper by referring to Aldous Huxley's analogous idea of the brain as a reduction valve of consciousness. They wrote: "This finding is consistent with Aldous Huxley's 'reducing valve' metaphor ... which propose[s] that the mind/brain works to constrain its experience of the world." To help you know precisely what Huxley's hypothesis was, here is a quote from pages 10 and 11 of his book The Doors of Perception and Heaven and Hell (2004 edition):
The suggestion is that the function of the brain and nervous system and sense organs is in the main eliminative and not productive. Each person is at each moment capable of … perceiving everything that is happening everywhere in the universe. The function of the brain and nervous system is to protect us from being overwhelmed … by shutting out most of what we should otherwise perceive or remember at any moment, and leaving only that very small and special selection which is likely to be practically useful.Also interesting is the researchers' observation that the highest de-activations of the brain occurred in areas associated to what we normally call "ego functions;" namely, the default-mode network. This is consistent with the age-old idea that the ego prevents us from seeing reality as it truly is; from perceiving the unity and transcendence of conscious experience. As I wrote earlier in this blog, I like the metaphor of the brain as a whirlpool of consciousness, which localizes consciousness like a whirlpool localizes the water of a stream. When I read this part of their paper, I couldn't help but visualize the de-activation of the ego functions as analogous to someone inserting one's hand in a whirlpool, disrupting the "loopy" flow that maintains it, and thereby allowing the water molecules originally trapped in it to escape.
Technically, the study seems extremely well designed. To counter the uncertainties of measuring brain activity with an fMRI scanner, the researchers used two different signals: Arterial Spin Labelling (ASL) and a Blood-Oxygen Level-Dependent (BOLD) signal. The results across the two were consistent. Several other protocols were used to tackle each conceivable loophole and ensure the reliability of the results. Moreover, the researchers were able to explain why earlier studies on the effect of psychedelics on brain activity seemed to lead to different conclusions: Because earlier studies used PET scan measurements over much greater time scales, they may have detected merely a "rebound" of the psilocybin effects on glucose metabolism. All in all, the study is compelling and clearly carried out with great care and professionalism.
To conclude, I think that, although this research represents a milestone in our understanding of the relationship between mind and brain, it is just one study. Its results must be replicated before definite conclusions can be arrived at. Yet, there is a broader pattern associating peak subjective experiences with reduced blood flow to the brain, as I wrote in another article. Taken together, this study and that broader pattern are extremely compelling. They strongly indicate that the brain is a mechanism for limiting and localizing consciousness, but does not generate consciousness. When some specific brain functionality is taken out, consciousness relaxes and expands. Death, seen this way, may be the ultimate liberation of subjective experience.