I've just been watching DMT The Spirit Molecule with some interest, mainly in the hope of discovering what is known about the chemical and how it affects the brain. It starts out well, with a lot of attention paid to ayahuasca and the shamanistic traditions. Throughout the documentary people describe their experiences under the influence of DMT during scientific tests under controlled conditions. While individual experiences differ markedly, the overall consensus is that there is a lingering sense of wonder, amazement, and improved optimism following its use.
It strikes me in watching this how intensely literally people take the "places" and "experiences" that they have "outside of time" and in altogether "alternate universes." You can't blame them for their enviable enthusiasm, because it's true that DMT makes your brain feel like it's gone through "a thousand years of experience" without the sticky constraints of having to be you, or anyone in particular.
I haven't tried DMT, but I have experienced the very similar effects of Salvia divinorum, and I can attest to all of the above. I left my body but retained a sense of existing, though I had no identity. The concept of time –before and after– became completely meaningless, as did any ability to conceive of self and other. You might say that every mechanism of differentiation or discernment was tuned way way down. Other commonly-reported experiences also came with it, such as the sense of a separate presence, or two, a vision of the universe as a vast living machine, etc.
After subsequent experiences with Salvia I came to the definite conclusion that all these experiences are taking place in the brain, brought on by the chemical, and that the actual content and sensory stuff that people bring back from the experience is entirely synthetic. It doesn't mean in any sense that these experiences aren't highly valuable, but I think it is a mistake to take one person's subjective report about what they saw, heard, and felt, as being anything other than the resultant contents of their brain, which is now re-composed very much as if it had actually had these experiences, as if such experiences were possible in the world that our bodies occupy.
This is one of the great things about the brain. It is a continuous reality generator, and most of the time it deals with inconsistencies and incongruities in our experience by filling in the gaps. In fact it does this continually, to build a picture of the here and now from fragments of our long and short-term memory, from visual images entering the eye, sounds, smells, the temperature, etc., etc. The physical world is real, and our brains are firmly embedded in the physical world. Consciousness is not separate from chemistry, cellular respiration, and neuronal activity. I think DMT The Spirit Molecule actually makes a strong case for this, and simultaneously it's an exhibit of the strong social desire —even of scientists— to take the subjective reports of others literally and give them the same level of credence that the original witness does. We are polite beings to the core, at some level, and a person beaming with a thousand years of transcendent experience is the kind of person to whom we naturally defer.
As I said, I think these experiences are valuable. DMT experiences improve people's sense of well-being and gratitude, feelings of universal connection, personal resilience, optimism, and sociability. They help people to let go of past hurt and fears, and, as a rite of passage, to move forward with their lives and to reconnect with their core selves, beyond limiting conceptions. In short, it is a dose of enlightenment, in the transcendent sense. But in the intellectual sense, the scholarship on DMT is a muddle.
We can't tell people not to take their very vivid experiences as "mere hallucinations," nor should we. The visceral quality of any experience is what lends it its significance, and very often these experiences yield a treasure of unexpected associations and insights. But I think it's important for anyone really seeking to understand how the brain makes consciousness to utilize Dan Dennett's hetero-phenomenological approach for these subjective experiences. From dozens or hundreds of personal reports, we can begin to build a stronger picture of which activities of consciousness are being augmented or dampened by DMT, and correlate those elements with the regions of the brain being affected, which can be determined through FMRI and other technologies arriving in the coming decades.
DMT The Spirit Molecule is not wrong in describing the phenomenon as "spiritual" but I think it's a mistake to connect that with the usual superstitious meaning of the word, which literally invokes spirits from other realms, communication from ancestors, and the usual complement of mythical creatures. What is called "spiritual" here is altogether 100% psychological and physiological. DMT reveals very uncommonly-witnessed aspects of the human potential, which is usually constrained within the personality, which is the activity of relating to the outside world. And for the subjects themselves, it permits a synesthesia that's almost always suppressed, except possibly in sleep, and then only in some brain regions. So, when we discuss "spiritual" transformation we're talking about a marked change in personality that takes place as a result of the experience. The person's voice and hair color won't change, but they get many of the benefits of spiritual exertion without all the exertion, and so they may suddenly make a big life change, do the thing they've been putting off for too long.
When the word "spiritual" comes into play people get caught up in a classic inversion of reality, which I think is completely wrong, but which others feel very strongly about. From the materialist perspective, there is only the physical energy of the universe, and this energy generates all the phenomena that we know and love, including the brain. The experiences of the brain are thus coterminous with the physical processes of the brain. Conscious states are physical states. The "spiritualist" stance might say that physical reality can't be proved to exist out there, and therefore consciousness and the mind could very well be the primary constituent of reality. So a spiritualist would say that when someone takes DMT their consciousness really does go to another continuum, or that it transcends this continuum. They are correct only in the sense that the physical brain and its metabolism of the DMT is happening in space and time, therefore consciousness is "traveling" as it changes, but it is definitely not bound to the usual neuronal limitations, and therefore it is not bound to this plane in the same sense that the brain itself is. The whole reason being, of course, that consciousness really is an epiphenomenon of the activity of the brain. So if the activity of the brain is affected, the consciousness is affected. In the case of DMT the personality has a few minutes to cobble together a consistent narrative for its experiences of late, including making sense of space, time, and self, and in doing so it coalesces meaning from a flood of near chaos.
Until we establish more formal definitions, and maybe add some modifiers, there's always going to be a muddle concerning the concepts of things like free will, consciousness, and determinism. Most of our terms are too broad and more philosophical than scientific. In the case of determinism, quantum physics has rendered the debate meaningless. At the quantum level, the universe is non-deterministic. At the large scale it is largely deterministic. For some this opens the door to ever-more subtle consciousnesses subsisting at ever-smaller scales, which appear to our instruments of observation as quantum particles, waves, and strings. We have a strong prejudice against our minds being complex machines embedded in the physical world. And for most of us it's hard to imagine how it could really do what it does, it seems too miraculous.
If there is no spirit realm that we can visit hand in hand, but only these transcendent states of consciousness that we must experience entirely within our own minds, does that somehow make the universe out there mundane and limited? I personally don't feel that way. Profound experiences of self-transcendence are correlated with overcoming the past and moving forward with renewed purpose, and it doesn't seem to matter if you get there by prayer, climbing Everest, witnessing your first child being born, or ingesting Ayahuasca. They are all spiritual experiences.