One of the best ways to understand consciousness is to watch what happens when it changes. Sleep, psychedelics, meditation, and anesthesia each alter consciousness in distinct ways — and each reveals something about what consciousness depends on.
Before exploring altered states, it helps to understand the Default Mode Network (DMN) — a set of interconnected brain regions (medial prefrontal cortex, posterior cingulate cortex, angular gyrus, and others) that are most active when the brain is at rest.
The DMN is associated with:
The DMN is, in a sense, the neural basis of the self — the internal narrator that weaves your experience into a continuous story. And it turns out to be a key target of many altered states.
Classical psychedelics — psilocybin (mushrooms), LSD, DMT (ayahuasca), mescaline — work primarily by activating serotonin 5-HT2A receptors. Their effects on consciousness are profound:
A 2023 systematic review found consistent evidence that psychedelics reduce within-DMN connectivity and increase connectivity between the DMN and other networks — and that this reconfiguration correlates with both the intensity of subjective experience and therapeutic outcomes.
Psychedelics reveal that the sense of self — the feeling of being a unified "I" with a continuous narrative — is not a fixed feature of consciousness. It's a construct, generated by specific brain networks, that can be temporarily dissolved.
Consciousness persists during ego dissolution. People still experience. But they experience without the usual frame of self-reference. This suggests that selfhood and consciousness, while usually intertwined, are separable.
It also suggests that the "everyday" sense of self may function more like a filter — constraining consciousness to a manageable, survival-relevant subset of possible experience. Psychedelics loosen that filter.
Long-term meditation practice produces changes in consciousness that overlap remarkably with psychedelic states — but arrived at through training rather than pharmacology:
That psychedelics and meditation produce overlapping effects through completely different mechanisms — one pharmacological, one attentional — is significant. Both reduce DMN dominance. Both can produce ego dissolution. Both report experiences of consciousness without a stable self.
This convergence suggests the default self is a process, not a thing — something the brain actively constructs, and which can be deconstructed.
Every night, consciousness undergoes a radical transformation that we mostly ignore:
Dreams show that consciousness doesn't require external input. The brain generates a complete phenomenal world from its own activity. They also show that self-awareness and consciousness can come apart: in a normal dream you are conscious but not self-aware; in a lucid dream, self-awareness returns.
This dissociation is important for theories of consciousness. GWT struggles to explain dreams (what is being "globally broadcast" to whom?). IIT handles them more naturally (the brain's integrated information structure generates experience regardless of external input).
General anesthesia is the closest thing we have to a controlled experiment in consciousness elimination. Anesthetics don't just eliminate pain (that's local anesthesia) — they eliminate experience itself.
Key findings:
Anesthesia provides perhaps the strongest evidence that consciousness depends on integration — the brain's ability to combine information across regions into a unified whole.
Across all altered states, a consistent picture emerges:
Consciousness, selfhood, and self-awareness are three different things that usually come bundled together but can be pulled apart. Understanding how they come apart may be the key to understanding how they come together.