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Altered state of consciousness
Altered state of consciousness
Altered state of consciousness
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An altered state of consciousness (ASC),[1] also called an altered state of mind, altered mental status (AMS) or mind alteration, is any condition which is significantly different from a normal waking state. It describes induced changes in one's mental state, almost always temporary. A synonymous phrase is "altered state of awareness".

History of the term

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By 1892, the expression was in use in relation to hypnosis,[2] though there is an ongoing debate as to whether hypnosis is to be identified as an ASC according to its modern definition. The next retrievable instance, by Max Mailhouse from his 1904 presentation to conference,[3] however, is unequivocally identified as such, as it was in relation to epilepsy, and is still used today. In academia, the expression was used as early as 1966 by Arnold M. Ludwig[4] and brought into common usage from 1969 by Charles Tart.[5][6]

Definitions

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There is no general definition of an altered state of consciousness, as any definitional attempt would first have to rely on a definition of a normal state of consciousness.[7] Attempts to define the term can however be found in philosophy, psychology and neuroscience. There is no final consensus on what the most accurate definition is.[8] The best-established and latest definitions are provided below.

Arnold M. Ludwig attempted a first definition in 1966.

An altered state is any mental state(s), induced by various physiological, psychological, or pharmacological maneuvers or agents, which can be recognized subjectively by the individual himself (or by an objective observer of the individual) as representing a sufficient deviation in subjective experience of psychological functioning from certain general norms for that individual during alert, waking consciousness.[9]

Starting from this, Charles Tart focuses his definition on the subjective experience of a state of consciousness and its deviation from a normal waking state.

Altered states of consciousness are alternate patterns or configurations of experience, which differ qualitatively from a baseline state.[note 1][10]

Farthing's definition of an altered state of consciousness (ASC) is based on Charles Tart's terminology. Charles Tart described an altered state of consciousness as a profound change in the "overall pattern of subjective experiences".[11] In order to define an ASC, Tart focuses on the importance of subjective experience.

Farthing adds to his definition that an ASC is short-termed or at least reversible and that it might not even be recognized as an ASC at that moment. His definition relies only on subjective experience, leaving aside behavioral changes and physiological response.

An altered state of consciousness (ASC) may be defined as a temporary change in the overall pattern of subjective experience, such that the individual believes that his or her mental functioning is distinctly different from certain general norms for his or her normal waking state of consciousness. (Farthing, 1992, p. 205)

He lists fourteen dimensions of changed subjective experience. To account for an ASC, multiple dimensions need to be altered.[12]

A working definition for empirical research based on these previous definitions was by Schmidt in 2016:[7]

[Translated from German]: As a working definition for neuroscientific research, it might suffice to presume that most people have a strong intuition concerning which variability in their everyday wakeful state feels normal to them. This variability of experience is considered as normal fluctuation, while any state that is experienced to diverge significantly from it can be called an ASC. From an experimental perspective, it is also reasonable to compare ASC conditions to a baseline state – a state subjectively judged as average, or normal. The comparison with a 'normal' baseline requires that the ASC under investigation is of relatively short duration (minutes to hours), which differentiates ASCs from most pathological conditions. Importantly, it has been emphasized that an ASC is not a mere quantitative change in a single cognitive function (e.g. elevated arousal). Instead, it is a multidimensional phenomenon. Thereby, the relative intensity of multiple consciousness aspects constitutes a 'phenomenological pattern' characterizing a particular state. Such 'patterns' have also been referred to as relative changes in the '(basic) dimensions of consciousness'. For empirical research, such patterns correspond to a multivariate combination of independent 'consciousness factors', which can be quantified via questionnaires. The 'phenomenological pattern' results from the factor structure of the applied psychometric assessment, i.e. the individual ratings, or factor scores, of a questionnaire.

History

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History of utilization of ASCs

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Altered states of consciousness might have been employed by humans as early as 30,000 years ago.[10] Mind-altering plants and/or excessive dancing were used to attain an ecstatic or mystic state.[13] Examples of early religious use of altered states of consciousness are the rites of Dionysus and the Eleusinian Mysteries,[14] as well as yoga and meditation.[10] Followers of various shamanic traditions "enter altered states of consciousness in order to serve their community."[14] Terence McKenna has suggested that the use of psychedelic mushrooms in prehistoric times has led to the "evolution of human language and symbol use".[15] Some theorists propose that mind-altering substances, such as soma, might have pushed the formation of some of the world's main religions.[14][16]

Meditation in its various forms is being rediscovered by modern psychology because of its therapeutic potential and its ability to "enable the activity of the mind to settle down".[17] In psychotherapy, techniques like hypnosis and meditation support psychological processes.[18]

History of scientific study

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See also: Scholarly approaches to mysticism

Due to the behaviourist paradigm in psychology altered states of consciousness were dismissed as a field of scientific inquiry during the early 20th century.[19] They were pathologized and merely seen as symptoms of intoxication or demonic possession.[20]

Their return into psychology began with William James's interest into a variety of altered states, such as "mystical experiences and drug-induced states".[8] James' investigations into first-person-subjective-experience contributed to the reconsideration of introspection as a valuable research method in the academic community.[8]

The social change of the turbulent 1960s has decisively led to a change of the scientific perspective to the point that introspection as a scientific method and ASCs as valid realms of experience became more widely accepted.[21] Foundations for the research have been laid out by various scientists such as Abraham Maslow, Walter N. Pahnke, Stanislav Grof and Charles Tart.[22] They focused on seemingly beneficial aspects of ASCs such as their potential to "promote creativity or treat addiction".[9] Rather oppressive states such as dissociation from trauma were neglected.

The findings of the famous Good Friday Experiment by Pahnke suggest that mystical experiences can be triggered by psilocybin. Later investigations by Rick Doblin found that participants valued those experiences as "spiritual high points of their lives".[10]

In the midst of the rise of new-age subculture Stanislav Grof and others formed the new field of transpersonal psychology, which emphasized "the importance of individual human experience, validity of mystical and spiritual experience, interconnectedness of self with others and the world and potential of self-transformation".[23]

Abraham Maslow's research on peak experiences, as moments of "highest happiness and fulfillment",[23] further contributed to the depathologization of altered states.

A first summary of the existing literature was carried out by Charles T. Tart in his book Altered States of Consciousness, which led to a more common use of the term.[23] Tart coined the key terms discrete[note 2] and baseline states of consciousness, and thought about a general classification system for ASCs.[24] He also called for "state specific sciences"[10] in which researchers should do science on ASCs from within such states.

Classification

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A simple classification scheme for ASC. Sleep and dream states are distinguished from waking consciousness since they account for substantially different ways of the ability of memory formation and retrieval. Psychiatric diseases that go along with persistent changes of consciousness, like schizophrenia, are covered with the term "pathological conditions". In contrast, the classification scheme includes intended and induced ASCs as well as general fluctuations of neurotransmission, which are reversible and short-termed. One step further the graph suggests splitting induced ASCs in persistent and reversible states. Translated from German Schmidt & Majic.[7]

A classification of Altered States of Consciousness is helpful for comparing or differentiating induced ASCs and other variations of consciousness. Various researchers have attempted the classification into a broader framework. The attempts of classification discussed in the following focus on slightly different aspects of ASCs. Several authors suggested classification schemata with regard to the genesis of altered states and with regard to the type of experiences:

A classification with five categories was suggested by Dieter Vaitl[25] to distinguish ASCs according to how they were induced:

  • Pathological (Epilepsy, brain damage)
  • Pharmacological (psychoactive substances)
  • Physical and physiological (fasting and sex)
  • Psychological (music, meditation, hypnosis)
  • Spontaneous (day-dreaming and near death experience)

Vaitl[26] further suggests four basic aspects of experiences: (1) activation (2) awareness span (3) self-awareness (4) sensory dynamics. Alternatively Roland Fischer[26] suggests a classification along ergotropic (i.e., ecstasy) or trophotropic (i.e., meditation) properties. The work of Adolph Dittrich[26] aimed to empirically determine common underlying dimensions of consciousness alterations induced by different methods, such as drugs or non-pharmacological methods. He suggested three basic dimensions, which were termed: (1) oceanic boundlessness (2) dread of ego dissolution (3) visionary restructuralization. Further, Ken Wilber[10] proposes a multidimensional system and adds that the individual experience of an ASC is shaped by a person's unique psychological development.

Michael Winkelman argues that there are four different "modes of consciousness": (1) the waking mode (2) the deep sleep mode (3) the REM sleep / dreaming mode (4) the integrative mode.[27] Within this framework, many ASCs (psychedelics, hypnosis, meditation, etc.) are defined as belonging to the integrative mode.

Induction methods

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Pharmacological

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An altered state of consciousness may be defined as a short-term change in the general configuration of one's individual experience, such that the rational functioning is clearly altered from one's usual state of consciousness.[28] There are many ways that one's consciousness can be altered, such as by using psychoactive drugs, which are defined as chemical substances that pass through the blood-brain barrier and disturb brain function, causing changes in awareness, attitude, consciousness, and behavior.[28]

Cannabis is a psychoactive drug that is known to alter the state of consciousness. Cannabis alters mental activity, memory, and pain perception. One who is under the influence of cannabis may experience degrees of paranoia, increased sensitivity, and delayed reactions not normal for their usual conscious state. A 2009 review of anxiety and cannabis studies concluded that "frequent cannabis users appear to have higher levels of anxiety than non-users," and that "a considerable number of subjects developed anxiety disorders before the first symptoms of cannabis dependence." That led researchers to believe that anxiety-prone people tend to use cannabis as a self-prescribed anxiety medicine, opposing the idea that cannabis is what's causing the anxiety.[29]

MDMA (ecstasy) is a drug that also alters one's state of consciousness. The state of consciousness brought about by MDMA ingestion includes a rise in positive feelings and a reduction in negative feelings (Aldridge, D., & Fachner, J. ö. 2005). Users' emotions are increased and inhibitions lowered, often accompanied by a sensation of intimacy or connection with other people.

Opioids are a class of drugs that alter consciousness. Examples of opioids include heroin, morphine, hydrocodone, and oxycodone. Opioids produce analgesia and often feelings of euphoria in users. Opioid abuse may result in decreased production of endorphins in the brain, natural pain relievers whose effects may be heightened by drugs.[30]

Cocaine alters one's state of consciousness. Cocaine affects the neurotransmitters that nerves use to communicate with each other. Cocaine inhibits the reuptake of norepinephrine, serotonin, dopamine, and other neurotransmitters in the synapse, resulting in an altered state of consciousness or a "high" (Aldridge, D., & Fachner, J. ö. 2005).

Lysergic acid diethylamide, or LSD, activates serotonin receptors (the amine transmitter of nerve urges) in brain matter. LSD acts on certain serotonin receptors, and its effects are most prominent in the cerebral cortex, an area involved in attitude, thought, and insight, which obtains sensory signs from all parts of the body. LSD's main effects are emotional and psychological. The ingester's feelings may alter quickly through a range from fear to ecstasy (Humphrey, N. 2001). This may cause one to experience many levels of altered consciousness. It has also been shown to induce ego death (or ego dissolution).[31][32]

Alcohol alters consciousness by shifting levels of neurotransmitters. Neurotransmitters are endogenous chemicals that transmit signals across a synapse from one neuron (nerve cell) to another "target" cell (often another neuron). Neurotransmitters can cause inhibitory or excitatory effects on the "target" cell they are affecting.[33] Alcohol increases the effect of the neurotransmitter GABA (gamma-Aminobutyric acid) in the brain. GABA causes slow actions and inaudible verbal communication that often occur in alcoholics.[30] Alcohol also decreases the excitatory neurotransmitter glutamate. Suppressing this stimulant results in a similar type of physiological slowdown. In addition to increasing the GABA and decreasing the glutamate in the brain, alcohol increases the amount of the chemical dopamine in the brain, which is one of the addictive causes of alcoholism.

Non-pharmacological

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Altered states of consciousness may also be induced by:[original research?]

Emotions influence behavior that alters the state of consciousness. Emotions can be influenced by various stimuli.[34]

Pathologies/other

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Pathological or accidental induction may refer to unforeseen events or illnesses. According to Jeffrey R. Avner, professor of clinical pediatrics, a crucial element to understanding accidental and pathological causes of altered states of consciousness (ASCs) is that it begins with reduced self-awareness followed by reduced awareness in the environment (2006). Those with personal experience of conditions such as Depersonalisation often cite the opposite, that it is an increased awareness of the environment and the self that results in altered states of consciousness.[35] When the reduction of self-awareness and environmental awareness take effect, they produce altered states of consciousness. The specific conditions below provide clarity on the types of conditions compromise accidental and pathological causes.

Traumatic experience

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The first condition, traumatic experience, is defined as a lesion caused by an external force (Trauma. (n.d.) In Merriam-Webster Dictionary online, 2013). Examples include impact to the brain caused by blunt force (i.e., a car accident). The reason a traumatic experience causes altered states of consciousness is that it changes how the brain works. The external impact diverts the blood flow from the front of the brain to other areas. The front of the brain is known as the prefrontal cortex responsible for analytical thought (Kunsman, 2012). When the damage becomes uncontrollable, the patient experiences changes in behavior and impaired self-awareness. This is exactly when an altered state of consciousness is experienced.[36]

Epilepsy

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Another common cause of ASCs is epilepsy. According to Medlineplus[37] epilepsy is as a brain disorder that causes seizures (2013). During the seizure, the patient will experience hallucinations and loss of mental control,[38] causing temporary dissociation from reality. A study that was conducted with six epileptic patients and used functional magnetic resonance imaging (fMRI) detected how the patients did indeed experience hallucinations while a seizure is occurring.[39] This not only altered the patient's behavioral pattern but also made them dissociate from reality during that particular time frame.

Oxygen deficiency

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Oxygen deficiency impacts the brain, which is why ASCs can occur when there is oxygen deprivation in an environment.

Infections

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In addition to oxygen deprivation or deficiency, infections are a common pathological cause of ASC. A prime example of an infection is meningitis. The medical website WEBMD[40] states that meningitis is an infection that causes the coverings of the brain to swell. This particular infection occurs in children and young adults. This infection is primarily viral. Viral meningitis causes ASC and its symptoms include fevers and seizures (2010). The Impairment becomes visible the moment seizures begin to occur, this is when the patient enters the altered state of consciousness.

Sleep deprivation

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Sleep deprivation is also associated with ASCs, and can provoke seizures due to fatigue. Sleep deprivation can be chronic or short-term depending on the severity of the patient's condition. Many patients report hallucinations because sleep deprivation impacts the brain. An MRI study conducted at Harvard Medical School in 2007 found that a sleep-deprived brain was not capable of being in control of its sensorimotor functions,[41] leading to impaired self-awareness. Patients were also much clumsier than if they had not been experiencing sleep deprivation.

Fasting

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Fasting is another form of deprivation. Fasting can be deliberate, including for religious reasons or from psychological conditions such as anorexia.[42] Fasting refers to the ability to willingly refrain from food and possibly drinks as well. The dissociation caused by fasting is not only life-threatening but it is the reason why extended fasting periods can lead to ASC. Thus, the temporary dissociation from reality allows fasting to fall into the category of an ASC following the definition provided by Avner (2006).[43]

Psychosis

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Another pathological cause is psychosis, otherwise known as a psychotic episode. Psychotic episodes often include delusions, paranoia, derealization, depersonalization, and hallucinations (Revonsuo et al., 2008). Studies have not been able to clearly identify when a person is reaching a higher level of risk for a psychotic episode (Schimmelmann, B., Walger, P., & Schultze-Lutter, F., 2013),[44] but the earlier people are treated for psychosis the more likely they are to avoid the devastating consequences which could lead to a psychotic disorder (Schimmelmann, B., Walger, P., & Schultze-Lutter, F., 2013).[44] Unfortunately, there are very few studies which have thoroughly investigated psychotic episodes, and the ability to predict this disorder remains unclear. (Schimmelmann, B., Walger, P., & Schultze-Lutter, F., 2013).[44]

Reviewing the previous conditions for accidental and pathological causes, we can come to understand that all of these accidental or pathological causes share the component of reduced self-awareness. Therefore, ASCs cannot only be caused naturally but they can be induced intentionally with methods including hypnosis meditation, amongst others. There are also ASCs which are caused by less recreational purposes; people who utilize illegal substances, or heavy dosages of medications, as well as large amounts of alcohol, can indeed comply with the definition of an ASC (Revonsuo et al., 2008).

Neurobiological models of altered state experiences

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Entropic brain hypothesis

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See also: Default mode network, Psychosis, and Psychedelic drug

The entropic brain hypothesis by Robin Carhart-Harris in 2014[45][46][47] is a theory informed by neuroimaging research that uses the hallucinogen-induced neurological state to make inferences about other states of consciousness. The expression "entropy" is applied here in the context of states of consciousness and their associated neurodynamics, where high entropy means a high level of disorder. The theory proposes a general distinction between two fundamentally different modes of cognition, referred to as primary and secondary consciousness.

Primary consciousness is associated with unconstrained cognition and less ordered (higher-entropy) neurodynamics that preceded the development of modern, normal waking consciousness in adults. Examples include the rapid eye movement sleep (REM),transcendental state between REM sleep and sensory awareness(the psychedelic state), or the onset phase of psychosis. Secondary consciousness is associated with constrained cognition and more ordered neurodynamics. Examples include normal waking consciousness, the anesthetized or the depressed state.

The theory further proposes that via pharmacological induction of psychedelic substances psilocybin, the brain is able to enter into the primary state of consciousness (the psychedelic state) from normal waking consciousness. This "phase transition" between these two fundamentally different poles of consciousness is facilitated by a collapse of the normally highly organized activity within the default mode network (DMN) and a decoupling between the DMN and the medial temporal lobes (MTLs), which are normally significantly coupled.[47] The DMN is closely associated with higher-order cognitive functions such as supporting the neurological basis for the self (e.g. self-reflection, subjectivity, introspection), thinking about others (e.g. theory of mind), remembering the past and thinking about the future (e.g. episodic memory). Task-positive networks are associated with the inverse of these things e.g., focus on and scrutiny of the external world.

The entropic brain hypothesis emphasizes the great research potential of the psychedelic state of mind for gaining more insight into general human consciousness.

CSTC-loop

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See also: Sensory gating, Psychosis, and Psychedelic experience

Extensive scientific investigation on altered states of consciousness and their relationship to drug interactions with receptors in the brain have been performed. Particularly the study of the neurotransmitter serotonin and the effects of psychedelic drugs on the brain has been intensively researched over the past sixty years. It has been hypothesized that hallucinogens act either as an antagonist or an agonist at 5-HT2A (serotonin-2A) receptors and will elicit a state that shares some common phenomenological features with early acute stages of the group of schizophrenia disorders.[48]

Findings implicate that abnormalities of serotonin function and the serotonergic system could be responsible for psychiatric disorders such as the spectrum of schizophrenia (gating) disorders and therefore, that serotonin agonist or antagonists might be useful in the treatment of disorders such as schizophrenia. To investigate the underlying causative neurotransmitter mechanisms of this phenomenon, the CSTC (cortico-striato-thalamo-cortical) loop model has been formulated based on empirical neurobiological work. It is indicated that the common hypofrontality (underactivation of frontal brain regions) and cortical activation pattern induced by serotonergic and glutamatergic hallucinogens is due to a common disruption of thalamic gating of sensory and cognitive information. The CSTC feedback loop plays a major role in gating or filtering out external and internal information to the cortex. Thereby it influences the regulation of the level of awareness and attention.

Disruption of the CSTC loop system is proposed to significantly influence information processing, for instance the ability to screen out, inhibit, filter, or gate extraneous stimuli and to direct selective attention to salient features of the environment. Failures of these attentional gating mechanisms might overload patients with the excessive processing of both sensory and cognitive stimuli, which could lead to a breakdown of cognitive integrity and difficulty in distinguishing self from non-self and failure to integrate an overwhelming flood of information. Descriptive elaboration of the mentioned effects can be found in the literature on schizophrenia as well as in descriptions of hallucinogenic drug action.

Despite strong evidence linking serotonin and psychosis, novel research indicates that some behavioral effects of drugs such as psilocybin appear to be independent of the classical 5-HT2A receptor-agonist actions, implying that the model described here is not the only underlying framework at play. Interdisciplinary research enterprises have set out to study the convergence of serotonergic and glutamatergic models of psychosis and dynamic neurotransmitter interactions, derived from the study of hallucinogenic drugs, in the future.[48]

Synthetic surprise

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Synthetic surprise is a theoretical concept explaining the altered states of consciousness induced by psychedelic substances like LSD and psilocybin. Central to this concept is the activation of the 5-HT2A receptor by psychedelics. The hypothesis suggests that these substances induce a state of synthetic surprise through the selective activation of the 5-HT receptors system, based on recent insights supporting a role of 5-HT in signaling surprise. This state aligns with the 'prediction error' in the predictive coding framework of brain function, where there's a discrepancy between the brain's expectations and the actual sensory input. The precision of this sensory data is crucial in modifying the brain's pre-existing beliefs or 'priors'. Under the influence of psychedelics, the interplay between top-down expectations and bottom-up sensory information is altered, leading to the characteristic changes in consciousness. Hallucinations in this context can be explained by the previously proposed "Strong priors" theory.[49] This understanding of synthetic surprise has significant implications for the clinical use of psychedelic substances. The ability of psychedelics to induce surprise is proposed to be central to their therapeutic potential, especially in disrupting maladaptive cognitive and perceptual patterns.[50]

See also

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Notes

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References

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Sources

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Further reading

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Altered state of consciousness

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An (ASC) is a temporary condition of psychological functioning that qualitatively differs from the normal waking state, involving changes in , , , or sense of self. These states manifest as shifts in the patterning of mental processes, often induced by physiological, pharmacological, or psychological factors, and have been empirically observed through neurophysiological markers such as altered wave patterns or connectivity in . Pioneering work by researchers like Charles T. Tart emphasized discrete ASCs as distinct modes of information processing, challenging reductionist views by highlighting their functional utility beyond . ASCs encompass a spectrum from everyday variations like or intense focus to profound experiences elicited by psychedelics, , or , each producing measurable deviations in subjective reports and objective biomarkers. Empirical studies, including those using EEG and fMRI, reveal distinct neural signatures, such as reduced activity in psychedelic-induced states, supporting causal mechanisms rooted in brain dynamics rather than mere epiphenomena. schemes propose dimensions like intensity, control, and emotional tone to systematize ASCs, aiding and interdisciplinary . Notable applications include therapeutic uses in psychedelic-assisted for conditions like depression, where ASCs facilitate insight and , backed by controlled trials showing efficacy over placebos. Controversies persist regarding demarcation from mental disorders, with some empirical data indicating ASCs' role in and problem-solving, countering dismissals as illusory or harmful; however, risks of dissociation or in vulnerable individuals underscore the need for rigorous, context-specific evaluation over ideological prohibitions. Recent revivals in research, driven by technological advances, affirm ASCs' relevance to understanding baseline , prioritizing causal neural models over speculative interpretations.

Definitions and Phenomenology

Defining Altered States of Consciousness

An altered state of consciousness (ASC) refers to a temporary deviation in an individual's psychological functioning that significantly differs from the ordinary waking state, characterized by changes in subjective of , environment, or the itself. These states are typically self-reported and involve qualitative shifts in , , or affect, distinguishable from baseline by the experiencer's own judgment of difference. Arnold M. Ludwig's 1966 analysis provided an early empirical framework, identifying 10 shared phenomenological dimensions across ASCs induced by diverse means such as , drugs, or : alterations in thinking (e.g., increased fantasy or illogical patterns), sense of time, , emotional tone, control over mental processes, feelings of pleasure or numbness, awareness of the environment, sense of reality of the phenomenal world, and capacity for memory or . Ludwig emphasized that these features manifest variably but converge to demarcate ASCs from normal states, based on clinical observations and experimental data from mid-20th-century studies. Charles T. Tart, building on such work, formalized ASCs as discrete patterns of mental structures and processes that maintain internal stability yet differ holistically from ordinary consciousness, often requiring specific induction to access state-specific knowledge or perceptions unavailable in baseline states. Tart's systems-oriented approach, detailed in his 1975 book States of Consciousness, posits that ASCs involve reconfiguration of psychological subsystems like and , supported by psychophysiological evidence from EEG and behavioral metrics showing distinct neural correlates. This definition underscores causal mechanisms, such as reduced sensory input or pharmacological modulation, that disrupt habitual cognitive filters, enabling empirical validation through reproducible shifts in brain wave patterns or response latencies.

Core Phenomenological Features

Altered states of consciousness (ASCs) exhibit core phenomenological features that distinguish them from baseline waking through qualitative shifts in subjective experience, encompassing changes in , , , self-boundaries, and temporal flow. These features arise across diverse induction methods, from pharmacological agents to meditative practices, and are empirically documented in systematic analyses of self-reports and behavioral observations. A foundational delineation comes from Arnold M. Ludwig's review, which synthesized reports from , drug-induced, and mystical states to identify recurrent hallmarks: alterations in thinking patterns, such as symbolic or illogical associations; disturbed time sense, including dilation, contraction, or timelessness; impaired attentional focus with narrowed or expanded awareness; heightened bodily sensations and modifications in , like feelings of or dissolution; shifts in emotional tone from profound to intense fear; and perceptual distortions, encompassing illusions, hallucinations, or . These elements reflect a reconfiguration of mental processes, often accompanied by reduced volitional control and increased suggestibility, as corroborated in subsequent and experimental studies of ASCs. More recent psychometric assessments, such as the 5-Dimensional Altered States of Consciousness Rating Scale (5D-ASC), operationalize these into measurable subscales, capturing oceanic boundlessness (dissolution of ego boundaries with unity experiences), visionary restructuralization (intensified and ), auditory alterations (enhanced or transformed ), anxious ego dissolution (threats to self-integrity with dread), and reduced vigilance (impaired reality testing and control). Empirical data from psychedelic and non-pharmacological inductions validate these dimensions' reliability, with factor analyses showing consistent loadings across participants, though intensity varies by context—e.g., trials report peak oceanic boundlessness scores exceeding 50% above baseline on visual analog scales. Such features underscore ASCs' departure from ordinary consciousness without implying , emphasizing instead adaptive or exploratory potentials in controlled settings.

Historical Development

Pre-Scientific and Cultural Contexts

In pre-scientific societies, altered states of consciousness were frequently interpreted as portals to spiritual realms, enabling interaction with deities, ancestors, or supernatural entities for purposes such as healing, divination, and communal guidance. These states were induced through rhythmic drumming, fasting, sensory deprivation, or ingestion of psychoactive plants, with practitioners like shamans serving as intermediaries who navigated these experiences to retrieve lost souls or combat malevolent forces. Archaeological evidence, including ancient medicinal plants from South American sites dated to at least 30,000 years ago, indicates early ritual use of hallucinogens to facilitate trance states for shamanic healing and prophecy. Shamanic traditions, documented across indigenous cultures from Siberia to Mesoamerica, emphasized voluntary entry into trance as a controlled technique for ecstatic flight or soul journeying, distinct from pathological dissociation. In Mesoamerican civilizations, such as the Olmec by 1500 BCE, shamans employed hallucinogenic substances like morning glory seeds and toad venom to access visionary states, as evidenced by iconography depicting transformed figures and ritual artifacts. Similarly, Siberian shamans used fly agaric mushrooms to induce altered perception, interpreting the resulting visions as direct communion with spirit guides, a practice corroborated by ethnographic accounts from the 18th century onward. In ancient Mediterranean contexts, priestesses at oracular sites like entered trance-like states, possibly via vapors from geological fissures or ritual fasting, to deliver prophecies attributed to Apollo, influencing decisions in Greek city-states from the 8th century BCE. These experiences were culturally framed not as mere psychological phenomena but as divine possession, with the Pythia's frenzied utterances requiring priestly interpretation. Cross-culturally, such practices underscore a near-universal pre-scientific recognition of ASCs as functionally adaptive for social cohesion and existential inquiry, though interpretations varied by worldview without empirical validation of supernatural claims.

Scientific Investigation and Key Milestones

The scientific study of altered states of consciousness emerged in the early through psychological inquiries into mystical and religious experiences. , in his 1902 work , systematically described these states as possessing four marks: (difficulty in verbal description), noetic quality (imparting insightful knowledge), transiency (short duration), and passivity (sense of being controlled by a ). James argued that such states reveal aspects of consciousness inaccessible in ordinary , advocating empirical respect for subjective reports despite their variability. This approach contrasted with prevailing materialist views, emphasizing first-person phenomenology as valid data for investigation. A pivotal physiological milestone occurred in 1953 when Eugene Aserinsky and identified rapid eye movement () sleep, establishing dreaming as a measurable ASC with distinct brain wave patterns and autonomic changes distinguishable from non-REM sleep. Their polygraphic recordings demonstrated that vivid dream reports correlated with REM epochs, enabling objective study of internally generated hallucinations and challenging prior assumptions that sleep was uniformly unconscious. This discovery spurred psychophysiological research into sleep cycles and laid groundwork for linking ASC to neural oscillations. In 1966, psychiatrist Arnold M. Ludwig published a seminal framework in Archives of General Psychiatry, defining ASC as any differing from normal waking consciousness along dimensions such as , affect, , and volition. Drawing from clinical data on , drugs, and , Ludwig identified 13 phenomenological parameters (e.g., alterations in , time sense, and reality testing) and hypothesized adaptive functions like enhanced or stress relief, while cautioning against overpathologizing them. His analysis integrated diverse inductions, promoting ASC as a legitimate research domain rather than fringe phenomena. The 1950s and 1960s saw intensive exploration of pharmacologically induced ASC via psychedelics. Albert Hofmann's 1943 self-administration of diethylamide () revealed its profound perceptual distortions, prompting clinical trials; by 1957, over 600 subjects had been studied for therapeutic potential in and anxiety. Humphry Osmond's 1957 coinage of "psychedelic" (mind-manifesting) followed experiments, leading to thousands of publications by 1965 on 's effects, including ego dissolution and . Concurrently, Charles T. Tart's 1969 edited volume Altered States of Consciousness synthesized findings from , , and , advocating discrete state models over continuum views. Research declined post-1971 due to U.S. scheduling and cultural backlash, halting most human trials until the revival. Key neuroimaging milestones followed: early (PET) scans in the linked psychedelics to serotonin receptor activation, while a 2006 study used structured interviews to quantify psilocybin-induced mystical experiences in 36 volunteers, replicating James' criteria with 60-70% reporting sustained positive changes. By 2012, functional MRI demonstrated psilocybin's reduction in integrity, correlating with subjective unselfing and entropy increases in brain signaling. These advances, prioritizing controlled designs over anecdotal reports, have informed causal models tying ASC to disrupted predictive processing and thalamocortical dyssynchrony.

Classification Approaches

Phenomenological and Dimensional Classifications

Phenomenological classifications of altered states of consciousness (ASC) emphasize qualitative shifts in subjective experience, distinguishing them from baseline waking awareness through clusters of introspective reports. Common features include perceptual distortions such as visual hallucinations, , or heightened sensory acuity; alterations in , like feelings of or dissolution; temporal disorientation, where time may contract, expand, or cease; emotional intensifications ranging from to terror; cognitive disruptions manifesting as hyperassociative or fragmented thinking; and changes in self-identity, including ego loss or oceanic unity. These characteristics, synthesized from clinical observations and self-reports across hypnotic, drug-induced, and meditative ASC, form the basis for identifying ASC as recognizably deviant patterns of inner experience. Arnold M. Ludwig's 1966 framework formalized 12 phenomenological criteria, including subjective alterations in volition, , and testing, which must occur to a marked degree for an ASC to be classified as such; these criteria have influenced subsequent phenomenological taxonomies by prioritizing experiential deviation over etiological factors. More recent syntheses cluster these features into broader phenomenological domains, such as perceptual restructuring, affective valence shifts, and self-boundary modifications, enabling cross-cultural and cross-modal comparisons of ASC induced by psychedelics, , or states. Such classifications underscore the heterogeneity of ASC phenomenology, where no single feature is universal, but combinations reliably signal departure from ordinary consciousness. Dimensional classifications model ASC as variations along quantifiable continua rather than binary or categorical shifts, often operationalized through validated psychometric scales that assess intensity of experiential dimensions. Charles T. Tart's systems-theoretic approach posits as an aggregate of subsystems (e.g., exteroception, , , ), with ASC emerging when parametric changes in multiple subsystems surpass a reconfiguration threshold, yielding a novel systemic state; this multidimensional view rejects unidimensional metrics like alone, emphasizing patterned deviations. Empirical scales like the OAV (Oceanic Boundlessness, Anxiety-Blissful Dread of Ego Dissolution, Visionary Restructuralization) quantify core phenomenological axes in drug-induced ASC, demonstrating high (Cronbach's α > 0.80) and factor structure stability across , , and sessions. The expanded 5D-ASC scale incorporates additional etiology-specific dimensions—auditory alterations and vigilance reduction—alongside the original three, facilitating nuanced profiling of ASC intensity and quality in psychedelic research; validation studies confirm its reliability (test-retest r > 0.70) and sensitivity to dose-response effects in controlled trials. These dimensional tools enable statistical mapping of ASC variability, revealing, for instance, that oceanic boundlessness correlates with default mode network desynchronization in neuroimaging, while visionary restructuralization aligns with sensory cortical hyperactivity. By treating ASC as graded phenomena, dimensional models support hypothesis-testing and integration with neurobiological data, though they risk oversimplifying gestalt-like holistic shifts emphasized in phenomenological accounts.

Functional and Etiological Categorizations

Altered states of consciousness (ASCs) are frequently categorized etiologically based on their originating causes or induction mechanisms, which aids in distinguishing underlying physiological, psychological, or pathological processes. A key framework delineates four primary etiological domains: spontaneous occurrences, such as drowsiness, daydreaming, hypnagogic , , dreaming, and near-death experiences; physically or physiologically induced states arising from factors like extreme environmental conditions (e.g., high altitude hypoxia), , sexual , or respiratory maneuvers like ; psychologically induced states elicited through techniques including , rhythmic induction via drumming or dancing, relaxation exercises, , , or ; and disease-induced states associated with conditions such as psychotic disorders, , or . This classification emphasizes the diversity of causal pathways, with spontaneous ASCs linked to natural fluctuations in levels and pathological ones often involving disrupted neural connectivity, as evidenced by altered gamma oscillations in . Etiological schemes extend to method-based categorizations, grouping ASCs by specific induction techniques, such as pharmacological agents (e.g., psychedelics or anesthetics) versus non-pharmacological methods like or , which facilitate targeted experimental studies of variations. In clinical contexts, etiologies for severely altered levels of , such as or , prioritize identifiable triggers like systemic infections (28.6% in settings), metabolic derangements (22.4%), or cerebrovascular events (13.4%), underscoring the need for causal to guide intervention. Functional categorizations of ASCs emphasize their behavioral, adaptive, or maladaptive roles rather than mere phenomenology, viewing them as "final common pathways" for diverse stimuli that serve purposes like emotional resolution, generation, or social bonding. Adaptively, ASCs facilitate in shamanic practices, acquisition of novel through mystical experiences, and group cohesion in ritualistic possessions; maladaptively, they enable escape from conflict via states or self-destructive outlets like rage-induced dissociation. These functions highlight ASCs' evolutionary utility in problem-solving and , though pathological variants may reflect underlying defects in sensory-motor or cognitive integration, as seen in trance states reducing exteroceptive input or heightened emotional arousal. Such perspectives integrate etiological origins with outcome-oriented assessments, informing therapeutic applications like for or psychedelics for psychological flexibility.

Induction Methods

Pharmacological Induction

Pharmacological induction of altered states of consciousness (ASC) relies on psychoactive substances that modulate activity, thereby disrupting normal patterns of neural signaling and perceptual processing. These agents primarily target serotonin, glutamate, or other systems, resulting in transient changes such as vivid hallucinations, distorted , and diminished self-boundaries, as evidenced by increased neural and signal in studies. Unlike endogenous or non-pharmacological methods, drug-induced ASC exhibit dose-dependent intensity and reversibility upon or clearance, with empirical data from controlled administrations confirming reliable phenomenological shifts across individuals. Classic serotonergic psychedelics, including lysergic acid diethylamide () and , bind agonistically to 5-HT2A receptors, promoting cortical desynchronization and enhanced sensory integration that manifests as , ego dissolution, and profound alterations in reality appraisal. , first synthesized in 1938 and subjectively tested by on April 19, 1943, induces these effects at doses as low as 20-30 micrograms, with (MEG) studies showing elevated spontaneous signal diversity indicative of expanded conscious states lasting 8-12 hours. , the active compound in certain mushrooms, similarly elevates brain entropy after conversion to psilocin, correlating with subjective reports of unity and transcendence in clinical trials involving 10-25 mg doses. These substances do not impair executive function or induce , distinguishing their ASC from pathological states. Dissociative anesthetics, such as , antagonize N-methyl-D-aspartate (NMDA) glutamate receptors, producing detachment from body and environment, often termed "dissociative anesthesia," alongside out-of-body experiences and . Administered at sub-anesthetic doses (e.g., 0.5 mg/kg intravenously), reliably triggers these effects within minutes, with meta-analyses of pharmacological studies confirming dissociation prevalence rates exceeding 70% in healthy volunteers. Unlike psychedelics, dissociatives can evoke near-death-like phenomena, supported by neural models linking NMDA to thalamocortical decoupling. Other categories, including cannabinoid agonists like delta-9-tetrahydrocannabinol (THC) from , induce milder ASC characterized by enhanced and sensory amplification at doses of 5-20 mg, via CB1 receptor activation, though effects vary widely due to tolerance and set-setting factors. Deliriants such as , which block muscarinic receptors, produce more chaotic, realistic hallucinations but carry higher risks of and , as documented in toxicological case series rather than controlled induction. Overall, pharmacological ASC induction underscores causal links between receptor-specific pharmacology and experiential phenomenology, with safety profiles differing markedly: psychedelics show low physiological toxicity in supervised settings, while risk emergence reactions.

Non-Pharmacological Techniques

Non-pharmacological techniques for inducing altered states of (ASCs) involve deliberate manipulations of , , or sensory input, often drawing on mind-body practices that have been empirically linked to phenomenological shifts such as , unitive experiences, or heightened absorption. These methods, including , , , and breathwork, produce ASCs through mechanisms like thalamo-cortical entrainment or reduced end-tidal CO2 levels, with rates indicating that up to 45% of regular practitioners encounter such states. Empirical studies, primarily from and self-report scales like the Altered States of Consciousness Rating Scale, demonstrate these techniques reliably deviate from baseline waking , though individual susceptibility varies based on factors like trait absorption. Meditation and practices, including and , frequently elicit ASCs characterized by disembodiment, unity, or bliss, with a 2024 randomized controlled trial showing 45% of participants reporting such experiences after eight weeks of training. Neuroimaging evidence reveals associated changes in cortical thickness and activity, supporting causal links to altered and via sustained attentional focus. These states arise from prolonged attentional regulation rather than mere relaxation, as evidenced by EEG shifts toward theta waves during deep practice. Hypnosis induces ASCs through and focused , with empirical data from susceptibility scales indicating enhanced responsiveness in highly hypnotizable individuals, leading to phenomena like time distortion or analgesia. While debates persist on whether it constitutes a distinct neurophysiological state versus , functional MRI studies show prefrontal deactivation and alterations consistent with reduced executive control and heightened immersion. Clinical trials confirm amplifies emotional intensity and absorption, though effects are moderated by and expectancy. Sensory deprivation via flotation-REST (restricted environmental stimulation therapy) tanks minimizes external inputs, prompting ASCs like vivid imagery or boundary dissolution in 60-80% of sessions lasting 60-90 minutes. Physiological measures, including reduced cortisol and EEG theta/delta increases, correlate with these shifts, attributed to deafferentation of sensory cortices and endogenous opioid release. A 2024 study quantified deviations using subscales for altered time sense and oceanic boundlessness, validating its induction reliability across participants. Breathwork techniques, such as holotropic or high-ventilation methods, hyperventilate to lower CO2 saturation, directly correlating with ASC onset via cerebral and pH shifts, as shown in a 2025 experiment where end-tidal CO2 drops predicted intensity (r = -0.65). Holotropic breathwork, involving rapid for 1-3 hours, mimics psychedelic effects through , with self-reports and biosensors confirming unitive states and emotional release in group settings. Empirical reviews link these to brainwave dominance, though risks like transient anxiety necessitate trained facilitation.

Pathological and Spontaneous Occurrences

Pathological altered states of consciousness (ASCs) arise as symptoms of underlying neurological or psychiatric disorders, often involving disrupted neural processing and impaired awareness. In , postictal states following seizures commonly feature altered consciousness, manifesting as confusion, unresponsiveness, or transient , with prevalence up to 80% in generalized tonic-clonic seizures due to cerebral exhaustion and imbalances. is characterized by persistent ASCs, including delusions, hallucinations, and disorganized thinking, linked to hyperactivity in mesolimbic pathways and structural abnormalities in prefrontal and temporal regions observed via . , often from metabolic derangements like or toxic exposures, induces acute fluctuations in and , affecting up to 80% of intensive care patients and correlating with diffuse cortical hypoperfusion. Other pathological instances include migraine auras, where triggers transient visual or sensory distortions resembling ASCs in 20-30% of sufferers, and sequelae like or , involving thalamocortical circuit damage. These states differ from induced ASCs by their involuntary onset and association with morbidity, though distinguishing them from adaptive responses requires etiological assessment, as some psychotic features in mimic but resolve post-seizure. Spontaneous ASCs occur without external induction or clear pathology, often in transitional physiological states. Hypnagogic hallucinations, experienced during the onset of , involve vivid visual, auditory, or kinesthetic in up to 70% of the general population, attributed to hybrid REM-wake neural activity in the reticular activating system. These brief episodes, lasting seconds to minutes, feature involuntary, emotionally charged perceptions without volitional control, distinguishing them from by partial . Near-death experiences (NDEs) represent another spontaneous form, reported by 10-20% of survivors, encompassing out-of-body perceptions, life reviews, and serene amid cerebral anoxia. Empirical studies indicate NDE memories exhibit high detail richness and emotional intensity comparable to real events, with some veridical elements like corroborated observations during clinical , though neurofunctional models attribute them to disinhibited activity and serotonin surges rather than metaphysical claims. Daydreaming and drowsiness also qualify as mild spontaneous ASCs, involving dissociated attention and mild perceptual shifts in 96% of individuals daily, driven by fluctuations without requiring sleep onset. Such occurrences highlight as a dynamic continuum, vulnerable to endogenous perturbations like or stress.

Neurobiological Mechanisms

Neural Correlates and Brain Imaging Evidence

(fMRI), (EEG), and (PET) studies have elucidated neural patterns underlying altered states of consciousness (ASCs), revealing disruptions in and increased signal complexity that correlate with subjective experiential changes. These modalities demonstrate reduced integrity in the (DMN)—comprising regions like the and medial involved in self-referential thought—across multiple ASCs, alongside elevated brain entropy, a measure of signal unpredictability reflecting diminished hierarchical constraints on information processing. Such findings suggest ASCs involve a relaxation of the brain's typical ordered dynamics, enabling novel perceptual and cognitive configurations, though correlational data preclude direct without targeted interventions like , which remain infeasible in humans. In pharmacologically induced ASCs, particularly psychedelics like and , fMRI reveals acute desynchronization of the DMN, with decreased within-network functional connectivity and increased between-network communication, persisting for weeks in some cases. EEG-fMRI during DMT infusion similarly shows widespread desynchronization and heightened entropy, aligning with reports of ego dissolution and vivid hallucinations. PET imaging corroborates reduced metabolic activity in DMN hubs during exposure, correlating with diminished subjective rumination. These patterns contrast with normal waking states' constrained DMN dominance, implying psychedelics perturb serotonin 5-HT2A receptors to broaden the brain's state repertoire. Non-pharmacological ASCs, such as , exhibit analogous yet distinct DMN hypoactivity; experienced practitioners show fMRI reductions in DMN engagement during focused attention practices, accompanied by EEG increases in (4-8 Hz) and gamma (30-100 Hz) power, indicative of heightened and sensory integration. , by comparison, involves fMRI alterations in executive-salience network connectivity and EEG shifts toward dominance, with meta-analyses identifying activation linked to heightened and perceptual distortions. Across these, metrics from fMRI and EEG quantify a common expansion in , supporting theories that ASCs emerge from unconstrained neural trajectories rather than localized activations. Pathological or spontaneous ASCs, like those in or near-death experiences, show parallel imaging signatures—e.g., transient DMN decoupling in seizures—but differ in and reversibility, highlighting context-dependent neural implementations. Limitations include small sample sizes in many studies and challenges in parsing state-specific from trait effects, underscoring the need for longitudinal, multi-modal designs to validate these correlates against phenomenological anchors.

Prominent Theoretical Models

Charles T. Tart's systems model conceptualizes a state of consciousness as comprising stable psychological structures—such as , , , and sense of identity—and variable processes that pattern these structures differently across states. In this framework, ordinary waking consciousness represents a baseline patterning, while emerge as discrete configurations where processes like or reality-testing shift, potentially enabling state-specific sciences with unique laws of operation. Tart's approach, outlined in his 1975 book States of Consciousness, emphasizes empirical observation of these shifts without assuming , drawing on from , , and psychedelics to argue for ASC as adaptive variations rather than mere aberrations. The entropic brain hypothesis (EBH), proposed by Robin Carhart-Harris and colleagues in 2014, posits that the quality of conscious states correlates with the of brain activity, measured via parameters like signal complexity and unconstrained dynamics. Under EBH, psychedelics such as elevate neural by disrupting hierarchical , reducing top-down constraints and fostering a more fluid, primary-process-like cognition akin to early development or REM sleep. evidence, including increased brain-wide connectivity and reduced integrity during LSD and sessions, supports this by showing rises correlating with subjective reports of ego-dissolution and vivid imagery. The model predicts therapeutic potential in high- states for rigid psychiatric conditions, though critics note measures may conflate noise with meaningful variability, requiring causal interventions for validation. Building on EBH, the relaxed beliefs under psychedelics (REBUS) model, formulated by Carhart-Harris and Karl Friston in 2019, integrates the free-energy principle to explain psychedelic effects as a relaxation of high-level priors in Bayesian brain inference. Psychedelics are theorized to flatten the brain's energy landscape, attenuating precise top-down predictions from prefrontal regions and amplifying bottom-up sensory signals, which manifests as perceptual anomalies and belief revision. fMRI data from psilocybin trials demonstrate decreased precision weighting of priors alongside enhanced primary visual cortex activity, aligning with reports of heightened sensory acuity and therapeutic insights in depression treatment. extends to non-pharmacological ASC like meditation by positing similar prior relaxation, but empirical testing remains limited to serotonergic agents, highlighting a focus on drug-induced states over broader etiologies. Global neuronal workspace (GNW) theory, adapted to ASC, suggests that consciousness arises from ignition and broadcasting of select information across fronto-parietal networks; disruptions in this process, as seen in psychedelics, yield fragmented or hyper-associated broadcasts. In a 2020 review, GNW frames psychedelic ASC as involving desynchronized workspace access, supported by EEG evidence of reduced P3b event-related potentials during exposure, indicating impaired global integration. This model underscores causal roles for thalamocortical loops but faces challenges in accounting for subjective unity in high-entropy states without additional mechanisms. Overall, these models converge on reduced hierarchical control as a hallmark of ASC, yet diverge in emphasizing psychological discreteness () versus neurodynamic fluidity (EBH/REBUS/GNW), with ongoing debates over generalizability beyond psychedelics.

Psychological and Cognitive Effects

Impacts on Perception, Cognition, and Emotion

Altered states of consciousness (ASCs) typically involve marked shifts in , ranging from intensified sensory experiences to distortions such as or hallucinations, particularly in pharmacologically induced states like those from psychedelics, where fMRI evidence shows increased neural entropy correlating with enhanced perceptual richness, including subjective reports of higher dimensions or 4D geometry in DMT experiences; these are attributed to brain chemistry effects without scientific validation of actual dimensional access and may entail psychological risks, with analogous spatial perceptual anomalies reported in deep meditation and lucid dreaming. In non-pharmacological ASCs, such as those from mindfulness meditation, perceptual alterations manifest as changed meanings ascribed to percepts or heightened unity with surroundings, with formal practice duration predicting intensity (marginal effect of 0.11 OAV points per hour, p=0.022). Hypnosis evokes perceptual changes through , including analgesia or time distortion, linked to transient brain disconnectivity observed in . Cognitive functions in ASCs exhibit both impairments and potential enhancements depending on the state. Drowsiness or anesthesia-like ASCs reduce EEG (e.g., Lempel-Ziv measures), impairing , memory, and executive control. Psychedelic ASCs disrupt cognitive integration via alterations, potentially increasing flexibility through 5-HT2A receptor agonism, though empirical support for gains remains mixed. Meditation-induced ASCs foster insightfulness (marginal effect of 0.12 OAV points per hour of formal practice, p=0.017) and disembodiment, with 28.8% of practitioners reporting the latter during sessions, though these correlate with baseline distress levels. Emotional experiences in ASCs often intensify, spanning euphoria, anxiety, or bliss. Psychedelics produce profound emotional shifts tied to serotoninergic mechanisms and altered thalamo-cortical connectivity, as evidenced by fMRI changes in fronto-parietal regions. In mindfulness-based programs, blissful states increase with practice (marginal effect of 0.30 OAV points per hour, p<0.001), while spiritual experiences heighten in predisposed individuals (marginal effect of 4.75 points, p=0.020). Hypnotic ASCs can evoke emotional detachment or heightened suggestibility-driven affect, with neurochemical underpinnings involving compromised metabolic processes. These effects vary by induction method, with pathological ASCs like those in disorders of consciousness showing reduced emotional reactivity due to impaired neural integration.

Changes in Self-Awareness and Reality Appraisal

Altered states of consciousness (ASCs) frequently involve profound modifications to , characterized by diminished boundaries between the self and external environment, often termed ego dissolution. This phenomenon manifests as a reduced sense of a distinct, autonomous "I," with individuals reporting feelings of unity or merging with surroundings, as validated through self-report scales like the Ego-Dissolution Inventory (EDI), which demonstrates strong psychometric reliability in psychedelic contexts. evidence links ego dissolution under to decreased integrity in the (DMN), a system implicated in self-referential processing, with correlations showing reduced connectivity in posterior cingulate and medial prefrontal regions during high-dose administration. In psychedelic experiences, these self-changes extend to altered bodily , where agonists like disrupt the integration of multisensory signals contributing to the embodied self, leading to reports of disembodiment or expanded self-boundaries. Empirical studies confirm that such dissolution correlates with increased attribution of to non-living entities, persisting as changes post-experience, as observed in controlled trials measuring pre- and post- surveys. Non-pharmacological ASCs, such as those induced by , similarly reduce self-referential awareness; for instance, prolonged chanting practices elicit ego dissolution alongside disrupted self-other boundaries, measurable via adapted scales showing heightened unity experiences. Reality appraisal in ASCs shifts toward derealization, where the external world appears dream-like, unreal, or hyper-real, often co-occurring with depersonalization—a detachment from one's own mental processes or body. In ketamine-induced states, dose-dependent derealization correlates with acute dissociative symptoms, mediated by glutamatergic modulation and linked to blissful states rather than distress in controlled settings. Hypnotic ASCs alter reality perception through suggestions that modify subjective monitoring of environmental cues, reducing the appraisal of ordinary reality as fixed, though less intensely than in psychedelics, as evidenced by psychophysiological measures of altered electrocortical activity. Pathological ASCs, such as in , feature chronic unreality appraisal tied to inhibited limbic responses, distinguishing them from transient, often positive, changes in induced states. These alterations challenge conventional dualistic appraisals of self versus world, with empirical scales like the Altered States of Consciousness Rating Scale capturing positively toned and unity, underscoring a continuum from dissolution to transcendence across ASC types. While self-report data predominate, convergence with supports causal roles for disrupted DMN and dynamics in these shifts, though longitudinal effects on enduring reality models require further validation beyond acute phases.

Therapeutic Applications

Historical and Emerging Clinical Uses

, an early method of inducing altered states of consciousness, emerged in clinical practice during the late 18th century through Franz Anton Mesmer's theory of , which involved trance-like states to treat ailments such as and pain when pharmaceutical options were scarce. Mesmer's techniques, practiced from 1774 onward, influenced subsequent developments, leading James Braid to coin the term "" in the 1840s and apply it systematically for surgical and psychological disorders. By the early , briefly incorporated into for before abandoning it in favor of free association, though it persisted in European clinics for and psychosomatic conditions. Psychedelic substances entered psychiatric use in the mid-20th century, with synthesized in 1943 and first administered therapeutically around 1949. From the 1950s to the mid-1960s, over 40,000 patients received LSD-assisted psychotherapy in the United States and for conditions including , where studies reported recovery rates up to 50% higher than controls, and anxiety associated with . These approaches involved high-dose sessions combined with talk to facilitate insight, but regulatory bans in the , classifying psychedelics as Schedule I substances, curtailed research amid cultural backlash. Contemporary clinical applications have revived interest in , particularly through , approved by the FDA as (Spravato) in 2019 for , inducing states that provide rapid symptom relief lasting about one week per infusion. MDMA-assisted therapy for (PTSD) advanced via phase 3 trials from 2017 to 2023, demonstrating 71% of participants achieving clinically significant reductions in symptoms after 2-3 sessions, though the FDA declined approval in August 2024 pending an additional trial due to concerns over blinding and safety data. , granted FDA status in 2018 for depression, shows promise in trials through 2025, with a 2024 study of clinicians reporting reduced depressive symptoms and burnout post-administration, alongside ongoing phase 3 evaluations for PTSD where 58% of participants experienced remission. continues in adjunctive roles, with a 2024 meta-analysis confirming it augments for anxiety and pain, achieving effect sizes 0.5-1.0 greater than therapy alone. These developments emphasize controlled, therapist-guided induction of altered states, though long-term efficacy and risks require further randomized controlled trials.

Empirical Evidence on Efficacy and Outcomes

Psychedelic-assisted therapies have demonstrated efficacy in randomized controlled trials (RCTs) for treating (PTSD) and (MDD). In a phase 3 RCT published in 2023 involving 104 participants with moderate to severe PTSD, MDMA-assisted therapy resulted in 71.2% of participants no longer meeting PTSD diagnostic criteria after 18 weeks, compared to 47.6% in the group, with significant reductions in symptom severity and functional impairment. Similarly, a 2023 RCT of single-dose (25 mg) with psychological support in 233 adults with MDD showed rapid and sustained antidepressant effects, with the Montgomery-Åsberg Depression Rating Scale (MADRS) score decreasing by 12 points more than at week 3, persisting to week 12 in responders. A 2024 of trials confirmed a significant benefit on depression scores versus (standardized mean difference -1.64, 95% CI -2.48 to -0.79), though heterogeneity and small sample sizes limit generalizability. Mindfulness-based interventions, which induce altered states through focused attention and non-judgmental awareness, exhibit moderate efficacy for reducing symptoms of anxiety, depression, and stress in meta-analyses of RCTs. A comprehensive 2014 meta-analysis of 209 studies found mindfulness-based therapy (MBT) superior to waitlist controls for anxiety (Hedges' g = 0.38) and depression (g = 0.30), with effects comparable to cognitive-behavioral therapy and pharmacotherapy in head-to-head comparisons, though maintenance over long-term follow-up varied. A 2023 individual participant data meta-analysis of mindfulness-based programs (MBPs) across 13 RCTs reported average reductions in depression (d = 0.48) and anxiety (d = 0.31) symptoms, with greater benefits in those with higher baseline severity, but wide individual variability suggesting non-response in subsets. These outcomes are attributed to enhanced psychological flexibility, though placebo effects and publication bias may inflate estimates in some reviews. Hypnotherapy, involving trance-like states of heightened , yields mixed empirical support across , with stronger evidence for and procedural anxiety than for core psychiatric conditions. A 2024 of RCTs on for depression identified short-term symptom reductions in small trials (e.g., Hamilton Depression Rating Scale improvements of 4-6 points), but lacked large-scale replication and showed inconsistent superiority over controls. For , a of seven RCTs reported hypnotherapy's superiority over supportive therapy (standardized mean difference -0.77 for symptom scores), with sustained benefits at 6-12 months in responders. Sleep outcomes in a 2018 review of 13 studies indicated benefits in 58% of trials (e.g., reduced latency and ), yet 29% showed no effect, highlighting dependency on and methodological variability. Across modalities, therapeutic outcomes in ASC interventions correlate with the intensity and subjective of the altered state, as evidenced by analyses linking mystical-type experiences in psychedelic trials to greater symptom relief (e.g., r = 0.35-0.52 for mood improvement). However, challenges include blinding difficulties in subjective-state trials, potential expectancy biases, and understudied long-term risks, necessitating larger, diverse-population RCTs for causal attribution.

Risks and Criticisms

Physiological and Psychological Hazards

Altered states of consciousness (ASC) induced by psychedelics carry acute physiological risks, including elevated heart rate, blood pressure, and body temperature, which can strain cardiovascular systems in individuals with preexisting conditions. , , and diaphoresis are common transient effects during peak experiences, with rare instances of more severe outcomes such as arrhythmias or seizures reported in uncontrolled settings. Breathwork practices, another pathway to ASC, can induce from , leading to symptoms like , muscle cramps, or syncope due to and ionized calcium imbalances. Prolonged or extreme to achieve ASC may result in , disturbances, and , exacerbating physical vulnerability during dissociative episodes. Empirical data from controlled psychedelic trials indicate that while serious physiological adverse events occur in under 1% of participants, these risks rise with polydrug use or underlying health issues, underscoring the need for medical screening. Psychological hazards of ASC include acute anxiety, , or , particularly in psychedelic-induced states, where up to 30% of users report challenging experiences akin to "bad trips" involving overwhelming fear or ego dissolution. Meditation-related adverse effects affect approximately 58% of practitioners, manifesting as heightened anxiety, , or re-experiencing of trauma, with 37% experiencing functional impairments. Retreat settings amplify these risks, with odds of unpleasant experiences 88.5% higher than in non-intensive practice. Long-term psychological sequelae encompass persistent depersonalization, , or (HPPD) following psychedelics, with case reports documenting schizophrenia-spectrum disorders in predisposed individuals. Emergent phenomena—sudden unusual mental or somatic experiences—correlate strongly with cumulative hours and prior psychedelic exposure, occurring in subsets of practitioners and potentially leading to dissociation or identity fragmentation without adequate support. , while generally low-risk, can engender false memories or suggestibility-induced distress in susceptible persons, though of enduring harm remains limited compared to other ASC modalities. These hazards are often underreported in research, as studies prioritize positive outcomes, potentially reflecting institutional biases toward therapeutic narratives over comprehensive . Vulnerable populations, including those with psychiatric histories, face elevated dangers of exacerbation or prolonged destabilization, necessitating caution in unsupervised pursuit of ASC.

Critiques of Hype and Methodological Flaws

Research on altered states of consciousness (ASCs), particularly those induced by psychedelics and mindfulness-based practices, has faced criticism for overstating transformative potential relative to empirical evidence. Proponents often claim profound shifts in perception, emotion, and self-awareness yield lasting therapeutic benefits, yet meta-analyses reveal inconsistent or modest effects, with media amplification portraying these interventions as near-panaceas without sufficient long-term data. For instance, mindfulness meditation studies have been accused of hype through sensationalized reporting of preliminary findings, such as equating benefits to pharmacological treatments despite trial shortcomings. A core methodological flaw stems from the inherent difficulty in blinding participants to ASC induction, as the vivid subjective alterations—hallucinations, ego dissolution, or heightened unity—render deception improbable, inflating expectancy biases and responses. In psychedelic trials for depression, approximately 50% exhibit some risk of bias from unblinding, with 44% rated high risk due to deviations from intended interventions, often because participants can discern active compounds from placebos. Similar issues plague research, where active controls are rare, allowing demand characteristics to confound outcomes. Small sample sizes further undermine reliability, with psychedelic studies typically involving 12 to 233 participants, limiting statistical power and generalizability while exaggerating effect sizes in early reports. Replication crises exacerbate this, as questionable practices like selective outcome reporting and multiple comparisons yield inflated positives, particularly in brain imaging of mystical experiences where confounds from self-reports persist. Conflicts of , prevalent in 76% of psychedelic authors in some analyses, correlate with fivefold higher odds of positive findings, fostering selective emphasis on benefits over risks. Critics highlight overreliance on subjective measures, such as questionnaires assessing "mystical" qualities, which suffer from retrospective distortion and cultural variability, obscuring causal links between ASCs and purported outcomes. Adverse effects, including meditation-induced anxiety or psychedelic transient distress (affecting 26-100% in trials), are underreported in 41.5% of cases, skewing risk-benefit profiles. Declining effect sizes over time, observed in analogous fields like antidepressants, suggest current hype may wane as larger, rigorous trials reveal smaller impacts.

Recent Developments and Future Directions

Advances in Research Since 2020

Research on altered states of consciousness (ASC) has accelerated since 2020, driven by advancements in and computational modeling that delineate neural mechanisms underlying subjective experiences. (fMRI) studies of psychedelics, such as and , have demonstrated increased global brain entropy and desynchronization of the , correlating with heightened ratings on the 5 Dimensions of Altered States of Consciousness (5D-ASC) scale, including oceanic boundlessness and visionary restructuralization. 00291-1) These findings, replicated across multiple trials, suggest psychedelics perturb hierarchical predictive processing, fostering novel perceptual integrations absent in baseline states. Synergistic investigations combining with psychedelics have revealed overlapping yet distinct connectivity patterns, with enhancing meditative insightfulness via reduced occipital-temporal distance in brain states, as measured by precision-weighted prediction errors. Randomized controlled trials indicate mindfulness-based protocols can induce ASC-like deviations in waking , characterized by ego dissolution and non-dual , supported by electroencephalographic (EEG) shifts toward gamma-band coherence. Meanwhile, studies on rhythm-induced ASC, such as drumming, highlight individual variability in susceptibility, linked to modulation and prefrontal hypoactivity, challenging uniform models of entrainment. In disorders of consciousness (DoC), post-2020 techniques like (DBS) and (tDCS) have shown preliminary in restoring , with meta-state EEG analyses revealing fragmented dynamics in vegetative states versus minimally conscious ones. Exploratory EEG work on lucid dreaming identifies elevated low-beta power during volitional control, enabling real-time protocols for therapeutic induction. Whole-brain simulations, integrating these datasets, propose ASC arise from perturbations in recurrent thalamocortical loops, testable via adversarial collaborations pitting global workspace against integrated information theories. These empirical strides underscore causal links between macro-scale network reconfiguration and phenomenal content, though longitudinal outcomes remain limited by small sample sizes and subjective reporting biases in self-assessments.

Open Questions and Empirical Gaps

Despite progress in , classification schemes for of consciousness (ASCs) remain inconsistent, with state-based approaches emphasizing subjective phenomenology, method-based ones focusing on induction techniques, and neurophysiological schemes prioritizing biological markers, complicating systematic comparisons and neural correlate identification. Open questions persist regarding the core phenomenological features most relevant for clinical applications and how to integrate these schemes into a unified framework. Empirical study of ASCs faces methodological hurdles, including the lack of standardized quantification tools and databases for subjective reports, which hinders in experimental induction across pharmacological, sensory, or meditative methods. Challenges in assessing multidimensional aspects—such as whether ASCs are unidimensional or involve distinct perceptual, cognitive, and self-related dimensions—further limit robust statistical analysis, often requiring over 10 minutes of neural data for reliability. Graded versus dichotomous in ASCs, particularly in transitions between and altered phenomenology, remain unresolved, with debates over discrete versus continuous processing. A key gap lies in linking neural signatures to phenomenology, as current models inadequately explain how local dynamics yield global alterations, with insufficient mechanistic accounts for phenomena like self-dissolution in or psychedelics. Whole-brain computational approaches show promise but struggle to simultaneously reproduce multiple observables, such as EEG complexity reductions in anesthesia-induced ASCs, highlighting needs for biophysical integration like receptor density mapping. The neurophenomenological divide—bridging first-person reports with third-person data—persists, especially for non-pathological ASCs. Individual variability in ASC responses, including predictors of therapeutic outcomes or risks like emergent psychological phenomena, lacks longitudinal empirical support, with gaps in understanding self-related alterations (e.g., minimal self in deep states) and their interplay with regulation. Future directions emphasize bottom-up modeling to test hypotheses on ASC transitions and critical dynamics, but empirical validation across diverse populations remains sparse post-2020.

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