Altered states of consciousness: Evolving terminology and clinical distinctions

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Altered states of consciousness encompass conditions in which awareness, perception, cognition, emotion, time sense, or responsiveness to the environment are significantly altered. For neurologists, precision in terminology is crucial to diagnosis, prognosis, and ethical communication. Over time, terminology has shifted from descriptive and cultural to operational and mechanistic. This blog entry reviews how that evolution occurred and how modern classifications organize these diverse states.

Historical and phenomenological terms

Early clinical neurology and psychiatry employed loosely defined descriptors, such as stupor, torpor, sopor, somnolence, lethargy, and obnubilation, to denote diminished alertness. These terms lacked objective criteria and have been largely replaced by standardized scales.

Coma, derived from the Greek kōma (deep sleep), remains in use to describe complete unarousable unresponsiveness with absent sleep-wake cycles. The term obtundation has partially replaced stupor in some classifications.

Such gradational vocabulary gave way to formal diagnostic entities during the late 20th century as neurobehavioral scales and imaging studies refined the assessment of consciousness.

Modern operational classifications

Jennett and Plum’s description of the vegetative state (1972) introduced a critical distinction between wakefulness and awareness: patients exhibited preserved eye opening and sleep-wake cycles but no purposeful responses. Later, the persistent vegetative state label was criticized for its dehumanizing tone and replaced by unresponsive wakefulness syndrome (Laureys et al 2010).

The minimally conscious state, defined in 2002, recognized partial but reproducible signs of awareness, such as command-following or purposeful movement. Subcategories (MCS− and MCS+) now distinguish the depth of preserved cognition. Emergence from the minimally conscious state is indicated by consistent communication or object use.

Together, coma, unresponsive wakefulness syndrome, and minimally conscious state are classified as primary disorders of consciousness.

Other altered states of consciousness

Other altered states include both normal physiologic phenomena and states that involve consciousness due to non-neurologic disorders, psychiatric or psychological conditions, and substances.

1. Physiological or naturally occurring states

These include normal variants of consciousness:

• Sleep (REM and non-REM)
• Dreaming and lucid dreaming
• Hypnagogic and hypnopompic transitions
• Daydreaming and mind-wandering
• Flow or deep absorption states
• Meditative and contemplative states
• Prayer or mystical religious ecstasy

These are associated with predictable neurophysiologic patterns such as thalamocortical oscillations and modulation of the default-mode network.

2. Pathological or clinical states

These include disorders directly relevant to neurologic practice:

• Coma
• Unresponsive wakefulness syndrome
• Minimally conscious state
• Locked-in syndrome (intact awareness but absent motor output)
• Delirium (hypoactive or hyperactive)
• Catatonia
• Dissociative or fugue states
• Seizure-related states (absence, complex partial)
• Psychosis or acute schizophrenia
• Functional or psychogenic unresponsiveness
• Near-death experiences
• Lazarus phenomenon (return of vital signs after cardiac arrest, distinct from spinal “Lazarus sign” reflexes)

3. Pharmacologically or externally induced states

These arise from psychoactive drugs, anesthesia, or environmental manipulation:

• Alcohol, cannabis, stimulants, sedatives, opioids
• Hallucinogens (LSD, psilocybin, mescaline, DMT)
• Dissociatives (ketamine, PCP, nitrous oxide, dextromethorphan)
• General or dissociative anesthesia
• Hypnosis, sensory deprivation, or sensory overload
• Virtual reality immersion, biofeedback, or breathwork techniques

4. Extreme emotional or situational states

Severe emotional arousal can also alter consciousness:

• Traumatic dissociation or freeze response
• Ecstatic or religious trance
• Erotic trance
• Shock and acute stress reactions
• Near-death experiences (overlapping with physiologic and psychological domains)

5. Special considerations

Some proposed extensions include:

• Default-mode network suppression states
• Meditative non-dual awareness
• Out-of-body experiences
• Sleep paralysis
• Hypnotic analgesia

Why terminology evolved

Terminological changes have aimed to increase conceptual precision and reduce moral or cultural bias. Older terms reflected philosophical or religious notions of “soul,” “trance,” or “possession.” Modern classifications rely on reproducible behavioral and neurophysiologic markers. The move from vegetative state to unresponsive wakefulness syndrome illustrates this ethical and scientific refinement. Functional MRI and PET have demonstrated covert awareness in some patients once labeled vegetative, underscoring the need for operational criteria.

Clinical assessment and distinction

Distinguishing among altered states depends on multimodal evaluation:

• Structured behavioral scales (Coma Recovery Scale-Revised)
• EEG and evoked potentials
• MRI and PET to assess the integrity of cortical and subcortical networks
• Longitudinal examination for reproducible purposeful behavior

Conclusion

The lexicon of altered consciousness has progressed from descriptive and moralized to mechanistic and ethically neutral. Modern neurology integrates physiologic, pharmacologic, and pathologic frameworks into a unified taxonomy of altered states. For clinicians, precision in language—anchored in observable data and neurobiologic evidence—remains essential for diagnosis, prognosis, and communication with families and multidisciplinary teams.

Further reading

Giacino JT, Ashwal S, Childs N, et al. The minimally conscious state: definition and diagnostic criteria. Neurology 2002;58(3):349-53. PMID 11839831

Gosseries O, Bruno MA, Chatelle C, et al. Disorders of consciousness: what's in a name? NeuroRehabilitation 2011;28(1):3-14. PMID 21335671

Jennett B, Plum F. Persistent vegetative state after brain damage. a syndrome in search of a name. Lancet 1972;1(7753):734-7. PMID 4111204

Laureys S, Celesia GG, Cohadon F, et al. Unresponsive wakefulness syndrome: a new name for the vegetative state or apallic syndrome. BMC Med 2010;8:68. PMID 21040571

Schiff ND. Recovery of consciousness after brain injury: a mesocircuit hypothesis. Trends Neurosci 2010;33(1):1-9. PMID 19954851

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