Consciousness

Consciousness is the continuous first-person field in which experience unfolds — the subjective what it is like to perceive, think, feel, and move through time. It is not a single faculty but an integrated background against which every mental event occurs.

Neuroscientists commonly distinguish two dimensions. The arousal dimension runs from deep loss of consciousness through sleep to alert wakefulness; this is roughly what medicine tracks when monitoring responsiveness, and what the clinical phrase loss of consciousness describes. The content dimension concerns what fills awareness — which perceptions, thoughts, and feelings are present, and how they cohere into a unified scene.

The term altered consciousness covers any change to either dimension — not just impairment, but heightened clarity, perceptual shifts, time alteration, and changes in the sense of self. Most of what substances and practices do to the mind can be mapped onto one or both axes.

How it works · its role

No single brain region generates consciousness. Evidence points to distributed networks — chiefly the thalamo-cortical system, which relays sensory signals and coordinates activity across the cortex — as the physical substrate for its moment-to-moment content.

One influential framework, global workspace theory, proposes that conscious awareness arises when information is broadcast widely across the brain, making it available to many cognitive systems at once. Unconscious processing, by contrast, stays local and compartmentalised. Another framework, integrated information theory, links consciousness to the degree of causal integration across neural circuits. Both remain actively contested.

What is well-established is that disrupting thalamo-cortical communication — through anesthetics, metabolic crisis, or severe injury — reliably removes conscious experience. The deeper question of how any neural process gives rise to subjective, first-person experience remains an open problem in both neuroscience and philosophy.

Relevance to substances & effects

Psychoactive substances alter consciousness through a range of mechanisms, and the character of that alteration depends on which neural systems they target.

Classic psychedelics — LSD, psilocin, mescaline — act primarily at serotonin 5-HT₂A receptors in sensory and prefrontal cortex, fragmenting the ordinary coherence of the conscious scene: perceptual distortions, dissolution of self-boundaries, and a changed relationship to time. Dissociatives such as ketamine block NMDA receptors, reducing the integration of incoming sensory signals; effects range from mild detachment to near-complete disconnection from the surrounding environment.

Depressants — alcohol, benzodiazepines, general anesthetics — suppress arousal and cortical activity broadly, moving consciousness toward sedation or, at high doses, loss of responsiveness. Stimulants increase dopaminergic and noradrenergic tone, sharpening the arousal dimension: awareness feels more focused and urgent.

Because consciousness is what every substance ultimately acts upon, its structure provides the organising logic for the effects taxonomy used throughout this encyclopedia.