ArticlePDF Available

The multi-dimensional approach to drug-induced states: A commentary on Bayne and Carter’s “dimensions of consciousness and the psychedelic state”


Abstract and Figures

Bayne and Carter argue that the mode of consciousness induced by psychedelic drugs does not fit squarely within the traditional account of modes as levels of consciousness, and favors instead a multi-dimensional account according to which modes of consciousness differ along several dimensions—none of which warrants a linear ordering of modes. We discuss the assumption that psychedelic drugs induce a single or paradigmatic mode of consciousness, as well as conceptual issues related to Bayne and Carter’s main argument against the traditional account. Finally, we raise a set of questions about the individuation of dimensions selected to differentiate modes of consciousness that could be addressed in future discussions of the multi-dimensional account.
Content may be subject to copyright.
The multi-dimensional approach to drug-induced
states a commentary on Bayne and Carter’s
“dimensions of consciousness and the
psychedelic state”
Martin Fortier-Davy
and Raphae¨l Millie`re
EHESS/ENS, Institut Jean-Nicod, 29 rue d’Ulm, Paris 75005, France and
Faculty of Philosophy, University of
Oxford, Radcliffe Observatory Quarter 555, Woodstock Road, Oxford OX2 6GG, UK
Both authors contributed equally to this manuscript.
*Correspondence address. Faculty of Philosophy, University of Oxford, Radcliffe Observatory Quarter 555, Woodstock Road, Oxford OX2 6GG, UK.
Tel: þ441865276926; E-mail:
Bayne and Carter argue that the mode of consciousness induced by psychedelic drugs does not fit squarely within the tradi-
tional account of modes as levels of consciousness, and favors instead a multi-dimensional account according to which
modes of consciousness differ along several dimensions—none of which warrants a linear ordering of modes. We discuss
the assumption that psychedelic drugs induce a single or paradigmatic mode of consciousness, as well as conceptual issues
related to Bayne and Carter’s main argument against the traditional account. Finally, we raise a set of questions about the
individuation of dimensions selected to differentiate modes of consciousness that could be addressed in future discussions
of the multi-dimensional account.
Key words: states of consciousness; pharmacology; philosophy; contents of consciousness; theories and models
In recent years, a debate has emerged regarding the adequate
characterization and taxonomy of global states of conscious-
ness, a notion that loosely refers to “ways of being conscious”
by contrast with specific conscious contents (Bayne and Hohwy
2016). Examples of global states of consciousness include the or-
dinary wakeful state, post-comatose disorders of conscious-
ness, and the dreaming state associated with rapid eye
movement sleep.
The traditional view in clinical neuropsychology is that
global states of consciousness can be ranked on a scale corre-
sponding to levels of consciousness, from the “least conscious”
to the “most conscious” state (Laureys 2005). This view has re-
cently been criticized by Bayne et al. (2016), on the grounds that
global states of consciousness differ from each other in more
than one respect, and thus cannot be easily ranked from least
to most conscious. Bayne et al. argue that consciousness is not a
1D construct measured by levels of consciousness, but a multi-
dimensional construct measured across several distinct
In a rich and thought-provoking article, Bayne and Carter
(2018) propose to extend this analysis to the states of conscious-
ness induced by psychedelic drugs such as psilocybin or lysergic
acid diethylamide (LSD). According to Bayne and Carter (hence-
forth B&C), available evidence from controlled studies does not
Received: 24 September 2019; Revised: 4 March 2020. Accepted: 7 March 2020
CThe Author(s) 2020. Published by Oxford University Press.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (
licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
For commercial re-use, please contact
Neuroscience of Consciousness, 2020, 6(1): niaa004
doi: 10.1093/nc/niaa004
Spotlight Commentary
Downloaded from by guest on 20 April 2020
warrant the claim that the kind of global state of consciousness
induced by psychedelics might constitute a higher level of con-
sciousness than ordinary waking awareness. Indeed, they argue
that the “psychedelic state” differs from ordinary wakefulness
in several respects, some of which qualify as “enhancements”
and others as “impairments.” They conclude that their analysis
further undermines the plausibility of a 1D account of global
states of consciousness in terms of levels of consciousness.
While we are very sympathetic to B&C’s multi-dimensional
framework and share the view that the effects of psychoactive
drugs challenge the level-based approach to global states of
consciousness, we emphasize here some potential limitations
of their account and offer some suggestions to address them.
Conceptual Preliminaries
Throughout their article, B&C refer to global states of conscious-
ness as states of consciousness or conscious states. It may be
useful to draw an explicit distinction between three notions
that this lexical choice might obscure for some readers:
1. Specific experiences individuated by their phenomenal char-
acter (“what it is like” to have them), often called “conscious
contents” or “local states of consciousness” (Chalmers 2010;
Bayne et al. 2016). In that sense, the visual experience of a
dog and the auditory experience of barking are two distinct
local states of consciousness, because what it is like to see a
dog differs to what it is like to hear a dog barking.
2. The subject’s overall phenomenology at a given time, i.e., the
totality of what it is like to be that subject at that time. This
notion has been called by different names, such as “total
experience” (Dainton 2000), “total phenomenal state”
(Gertler 2001;Bayne and Chalmers 2003), and “phenomenal
field” (Bayne 2010).
3. The subject’s “way of being conscious,” individuated by disposi-
tional properties such as the ability to be conscious of certain
kinds of contents, and the availability of those contents for the
control of cognition and behavior. In previous works, Bayne et al.
have variously referred to this notion as “background states of
consciousness” (Chalmers 2000), “modes of consciousness”
(Bayne and Hohwy 2016), and “global states of consciousness”
(Bayne et al. 2016).
In our opinion, it is better to avoid the expressions “state of
consciousness” and “conscious state” altogether, as they might
inadvertently prompt readers to conflate these three notions.
Furthermore, the expression “global state of consciousness” it-
self might lead some readers to confuse the second notion and
the third notion, insofar as they both refer to global features of
conscious subjects. In order to avoid potential confusions, we
propose to refer to these three notions as “local phenomenal
state”, “global phenomenal state”, and “global mode of con-
sciousness”, respectively. (“Global modes of consciousness”
seems more adequate than “modes of consciousness” simpli-
citer, to avoid confusion with modes of presentation or sensory
modalities, which both pertain to features of local phenomenal
states. We thank the anonymous reviewer for bringing this po-
tential confusion to our attention.) This choice of terminology
clearly distinguishes (i) local and global properties of conscious
subjects and (ii) categorical and dispositional properties of con-
scious subjects (phenomenal states vs. modes of
The Heterogeneity of Psychedelic Modes of
Throughout their article, B&C follow many other authors in re-
ferring to the “psychedelic state” as if it were a unified kind.
Although they briefly acknowledge that different psychedelic
drugs may have different effects on consciousness, they settle
on this expression “as a general term to refer to the paradig-
matic states of consciousness associated with the consumption
of psilocybin and LSD” (Bayne and Carter 2018, p. 2).
For authors who take the uni-dimensional account of global
modes of consciousness for granted, it might make sense to re-
fer to a unique global mode of consciousness induced by psy-
chedelic drugs. For example, if putative levels of consciousness
are indexed by the Lempel-Ziv complexity of spontaneous neu-
ral activity, as has been recently suggested (Schartner et al.
2017), then in so far as all psychedelic drugs increase spontane-
ous signal complexity in a similar way one can meaningfully re-
fer to the single mode of consciousness induced by such drugs.
(Let us emphasize again that we side with B&C’s criticism of
uni-dimensional accounts; we simply want to point out that
talking of a single psychedelic mode of consciousness makes
sense within such accounts, even if they are inadequate for dis-
tinct reasons.)
However, within B&C’s multi-dimensional account it might
not be helpful to refer to the paradigmatic global mode of con-
sciousness induced by psychedelic drugs in general, or even by
psilocybin and LSD in particular. Indeed, the effects of psyche-
delic drugs can vary dramatically on account of three main
Dosage: the same substance (e.g. LSD) can induce very different
kinds of effects depending on the dose (Shulgin and Shulgin
1997), and the relationship between dosage and subjective
effects is not always linear. For example, generally, (i) at a low
dose of LSD (between 25 mg and 75 mg), the world feel strange and
surprising (Nelson and Sass 2008) but no visual distortion is ex-
perienced (no illusions and no hallucinations); (ii) at a medium
dose of LSD (between 75 mg and 150 mg), real objects of the world
start morphing and illusory properties are projected onto them
(illusions with no hallucinations); (iii) at a high dose of LSD (150
mg and higher), genuine hallucinations (seeing objects which are
not in the real world) are experienced (Masters and Houston
Context and personal predispositions: the same dose and the
same compound taken in different settings or with different
mindsets can also induce somewhat distinct experiences
Provides a critical discussion of an influential new
model of global states of consciousness such as post-
comatose disorders of consciousness and drug-induced
Offers terminological and conceptual distinctions to ad-
vance the discussion of multi-dimensional accounts of
global states of consciousness.
Underlines empirical evidence challenging the claim
that there is a single paradigmatic global state of con-
sciousness associated with the effects of psychedelic
Raises a set of outstanding questions regarding the in-
dividuation of dimensions in multi-dimensional
accounts of global states of consciousness.
2|Fortier-Davy and Millie`re
Downloaded from by guest on 20 April 2020
(Hartogsohn 2016). Personality traits (such as absorption;
Studerus et al. 2012) and genetic factors (Ott et al. 2005) can also
significantly shape the effects of psychedelics.
Temporal dynamics: the effects of the same dose of the same
compound can change considerably across time (Preller and
Vollenweider 2018). Furthermore, there is a non-linear relation-
ship between the duration of drug intoxication and the associ-
ated subjective effects. For example, a high dose of N,N-
Dimethyltryptamine can first induce very salient bodily sensa-
tions, immediately followed by an abrupt loss of all bodily sensa-
tions (Timmermann et al. 2019).
According to B&C, the paradigmatic global mode of con-
sciousness induced by psychedelics is characterized by (i) per-
ceptual enhancements (increased bandwidth and vividness of
perceptual experience); (ii) cognitive impairments (impaired
decision-making, memory, attention, and abstract thinking);
and (iii) alterations of the experience of space, time, and self-
hood. (Note that talking of “impairment” and “enhancement”
generally makes sense by reference to a baseline performance
on a specific task. But, it is unclear whether such reference is
available for every dimension discussed by B&C, especially the
third one.) However, the evidence reviewed above suggests that
(at least) some of these dimensions could be “impaired” in one
psychedelic mode of consciousness and “enhanced” in another.
For example, psilocybin and LSD might increase the
“bandwidth” of sensory experience at low and medium to high
doses, thus scoring higher than the ordinary wakeful mode of
consciousness on the relevant dimension. However, there is
also evidence that high to very high doses of psilocybin and LSD
can lead to extremely impoverished sensory experiences.
(Consider for example the following anecdotal report describing
the effects of around 500 mg of LSD: “everything in my external
environment [was] turning black and red. I could barely see any-
thing, my vision was almost completely shot” (retrieved from As for the dimension related to the
sense of self in B&C’s account, there is evidence that low doses
of psilocybin and LSD can induce introspective moods with an
increased frequency of self-related thoughts, while medium to
high doses can lead to the temporary cessation of self-related
thoughts (Millie`re et al. 2018). Moreover, awareness of one’s
body can be “enhanced” at one time and “impaired” a few
minutes later, for the same subject, with the same drug and
dose (Timmermann et al. 2019).
This does not merely suggest that psychedelic drugs can in-
duce different global phenomenal states—which is trivially true
insofar as what it is like to be intoxicated by some psychedelic
drug at one time may differs from what it is like to be intoxicated
by some psychedelic drug at another time. Rather, available evi-
dence suggests that conscious subjects intoxicated by psyche-
delic drugs in general, and psilocybin and LSD in particular, can
vary significantly with respect to the dispositional properties
(e.g. dimensions) that individuate global modes of conscious-
ness, and that such variation does not always correlate linearly
with dosage. (Interestingly, a recent positron-emission tomogra-
phy imaging study also found that 5-HT2AR occupancy and
plasma concentration of psilocin—the active metabolite of psilo-
cybin—correlates non-linearly with the self-reported intensity of
subjective effects (Madsen et al. 2019).) Consequently, it might be
misleading to speak of a paradigmatic global mode of conscious-
ness induced by psychedelic drugs; even at a coarse-grained
level of analysis limited to B&C’s three dimensions, there is
some evidence that psychedelics can yield distinct global modes
of consciousness. We note that this is a strength of B&C’s
account rather than a limitation: unlike uni-dimensional
accounts, it allows us to capture the rich diversity of global
modes of consciousness that psychedelic drugs can induce.
Dimensions and Levels of Consciousness
In statistics, it is common to distinguish between quantitative
and categorical variables; the former can vary on an ordered
scale (like height), while the latter corresponds to nominal cate-
gories (like blood types). B&C seem to favor the claim that all
dimensions of consciousness are quantitative variables that
can be gradually “enhanced” or “impaired” compared to the
baseline of ordinary wakefulness.
Against the idea that the psychedelics can induce a “higher”
level of consciousness, they suggest that the global mode of
consciousness induced by psychedelic drugs scores higher than
ordinary wakefulness on one dimension and lower on another
(Fig. 1A). This argument relies upon the implicit assumption
that the global mode of consciousness induced by psychedelic
drugs could be considered to be a “higher” level of conscious-
ness than ordinary wakefulness only if it scored higher on all
dimensions (Fig. 1B).
It is worth noting that this assumption would be misguided if
the notion of levels of consciousness was incoherent anyway as a
matter of conceptual analysis—as Bayne et al. (2016) previously
suggested—because consciousness is not a gradable predicate like
height or temperature.(Consider by analogy the predicate being a
dog. Either an entity is a dog or it is not; even if a dog scored higher
than another on a number of dog-related dimensions—furriness,
speed, etc.—it would make little sense to say that such a creature
instantiates a higher level of dogginess, as it were.) Thus, we can
read Bayne et al. (2016) and Bayne and Carter (2018) as providing a
two-pronged strategy against levels of consciousness: they offer a
conceptual argument according to which the predicate “being con-
scious” is not gradable, and an empirical argument that comes into
play if the conceptual argument is judged unsatisfactory.
However, for the implicit assumption of the empirical argu-
ment to be sound, it must be the case that the three dimensions
of B&C’s account can be meaningfully compared and related;
otherwise, the fact that the psychedelic mode of consciousness
scores higher than ordinary wakefulness on all of these dimen-
sions would not be relevant to the debate on levels of con-
sciousness. Consider by analogy two individuals, Alice and Bob,
such that Alice scores higher than Bob on three dimensions re-
spectively related to wealth, height, and blood pressure. These
dimensions are not commensurable: there is no meaningful
way to aggregate the quantities of wealth, height, and blood
pressure instantiated by Alice and Bob in order to claim that
Alice scores higher than Bob on some overarching dimension.
If, on the other hand, all the dimensions discussed by B&C
can be meaningfully compared and related, then it should be
possible to aggregate scores on these dimensions even if—as
B&C argue—the psychedelic mode of consciousness scores
higher than ordinary wakefulness on a dimension related to
perceptual bandwidth, and lower on another dimension related
to cognitive function. But the availability of a meaningful aggre-
gation procedure of this kind would ultimately vindicate the no-
tion of degrees of consciousness. (Suppose that you want to
compare Alice and Bob on three dimensions related to well-
being, corresponding respectively to their happiness, mental
health, and sense of meaning—this example is adapted from
Alexandrova (2017). Insofar as these dimensions can be quanti-
fied and compared, it makes sense to say that if Alice scores
The multi-dimensional approach to drug-induced states |3
Downloaded from by guest on 20 April 2020
higher than Bob on all three dimensions, then Alice has a higher
level of well-being than Bob. But it is also intelligible to say that
if Alice scores significantly higher than Bob on the happiness
and mental health dimensions, but slightly lower than Bob on
the sense of meaning dimension, then Alice still has a higher
level of well-being than Bob overall.)
Individuating the Dimensions of Psychedelic
Although B&C’s model only contains three dimensions, addi-
tional variables might be relevant to characterize modes of con-
sciousness induced by psychedelics. For example, it has been
argued that the “sense of reality” is a central dimension of al-
tered states of consciousness and can crucially help classifying
them (Dokic and Martin 2012;Farkas 2014). In particular, includ-
ing a dimension related to the sense of reality could be helpful
to differentiate modes of consciousness induced by serotonergic
drugs from those induced by other hallucinogens—e.g. anticho-
linergics (Shanon 2002;Fortier 2018).
This final point raises broader questions: what are the individ-
uation criteria of the dimensions of conscious modes? On what
grounds should additional dimensions be introduced, or existing
dimensions subdivided? Is the dimensionality of the proposed
model merely dependent upon the desired fineness of grain of the
resulting taxonomy of conscious modes, or is there a optimal
number of dimensions that carves out modes of consciousness at
their natural joints? Such questions could be addressed in future
work building upon B&C’s important contribution.
Conflict of interest statement. None declared.
Alexandrova A. A Philosophy for the Science of Well-Being. New
York: Oxford University Press, 2017.
Bayne T. The Unity of Consciousness. Oxford: Oxford University
Press, 2010.
Bayne T, Carter O. Dimensions of consciousness and the psyche-
delic state. Neurosci Conscious 2018;2018. doi:10.1093/nc/niy008.
Bayne T, Chalmers DJ. What is the unity of consciousness? In:
Cleeremans A (ed.), The Unity of Consciousness. Oxford
University Press, 2003.
Bayne T, Hohwy J. Modes of consciousness. In: Sinnott-
Armstrong W (ed.), Finding Consciousness: The Neuroscience,
Ethics and Law of Severe Brain Damage. Oxford: Oxford University
Press, 2016.
Bayne T, Hohwy J, Owen AM. Are there levels of conscious-
ness? Trends Cogn Sci 2016;20:405–13. doi:10.1016/j.tics.2016.
Chalmers DJ. What is a neural correlate of consciousness? In:
Metzinger T (ed.), Neural Correlates of Consciousness. Cambridge,
MA: MIT Press, 2000, 17–39.
Chalmers DJ. The Character of Consciousness. Cambridge, MA:
Oxford University Press, 2010.
Dainton B. Stream of Consciousness: Unity and Continuity in
Conscious Experience. Cambridge, MA: Routledge, 2000.
Dokic J, Martin J-R. Disjunctivism, hallucinations, and metacog-
nition. Wiley Interdiscip Rev Cogn Sci 2012;3:533–43. doi:10.1002/
Farkas K. A sense of reality. In: MacPherson F, Platchias D (eds),
Hallucinations. Cambridge, MA: MIT Press, 2014, 399–417.
Fortier M. Sense of reality, metacognition and culture in schizo-
phrenic and drug-induced hallucinations: an interdisciplinary
approach. In: Proust J, Fortier M (eds), Metacognitive Diversity:
An Interdisciplinary Approach. Oxford/New York: Oxford
University Press, 2018, 343–78.
Gertler B. Introspecting phenomenal states. Philos Phenomenol Res
2001;63:305–28. doi:10.1111/j.1933-1592.2001.tb00105.x
Hartogsohn I. Set and setting, psychedelics and the placebo re-
sponse: an extra-pharmacological perspective on
Fig. 1The relationship between dimensions and levels of consciousness.
4|Fortier-Davy and Millie`re
Downloaded from by guest on 20 April 2020
psychopharmacology. J Psychopharmacol (Oxf, Engl) 2016;30:
1259–67. doi:10.1177/0269881116677852.
Laureys S. The neural correlate of (un)awareness: lessons from
the vegetative state. Trends Cogn Sci 2005;9:556–9. doi:10.1016/j.
Madsen MK, Fisher PM, Burmester D, et al. Psychedelic effects of
psilocybin correlate with serotonin 2A receptor occupancy and
plasma psilocin levels. Neuropsychopharmacology 2019;44:
1328–34. doi:10.1038/s41386-019-0324-9.
Masters REL, Houston J. The Varieties of Psychedelic Experience, 1st
edn. New York/Chicago/San Francisco: Holt, Rinehart and
Winston, 1966.
Millie`re R, Carhart-Harris RL, Roseman L, et al. Psychedelics,
meditation and self-consciousness. Front Psychol 2018;9:1–29.
Nelson B, Sass LA. The phenomenology of the psychotic
break and Huxley’s trip: substance use and the onset of
psychosis. Psychopathology 2008;41:346–55. doi:10.1159/
Ott U, Reuter M, Hennig J et al. Evidence for a common biological
basis of the absorption trait, hallucinogen effects, and positive
symptoms: epistasis between 5-HT2a and COMT
polymorphisms. Am J Med Genet B 2005;137B:29–32. doi:10.1002/
Preller KH, Vollenweider FX. Phenomenology, structure, and dy-
namic of psychedelic states. In: Halberstadt AL, Vollenweider
FX, Nichols DE (eds), Behavioral Neurobiology of Psychedelic Drugs.
Berlin, Heidelberg: Springer Berlin Heidelberg, 2018, 221–56.
Schartner MM, Carhart-Harris RL, Barrett AB, et al. Increased
spontaneous MEG signal diversity for psychoactive doses of
ketamine. LSD and psilocybin. Sci Rep 2017;7:46421. doi:10.
Shanon B. The Antipodes of the Mind: Charting the Phenomenology of the
Ayahuasca Experience. New York: Oxford University Press, 2002.
Shulgin A, Shulgin A. TIHKAL: The Continuation. Berkeley:
Transform Press, 1997.
Studerus E, Gamma A, Kometer M, et al. Prediction of psilocybin
response in healthy volunteers. PLoS One 2012;7:e30800.doi:10.
Timmermann C, Roseman L, Schartner M, et al. Neural correlates
of the DMT experience assessed with multivariate EEG. Sci Rep
2019;9:1–13. doi:10.1038/s41598-019-51974-4.
The multi-dimensional approach to drug-induced states |5
Downloaded from by guest on 20 April 2020
... Conscious experience, even conscious level, is not a monolithic entity, but an intricate amalgamation of many processes [52]. The view of consciousness as an aggregate phenomenon has evolved, with ever richer multidimensional descriptions gaining prominence [53][54][55]. Beyond this phenomenological argument, other mathematical arguments suggest that there are multiple ways in which information can be integrated in a system and thus that it is possible that no canonical measure of integrated information may exist, even in principle [43], emphasising the need to embrace multidimensional frameworks. ...
... Furthermore, there are many modes of information transfer within a complex system (Box 3) and each of these modes might usefully describe a distinct correlate of some aspect of consciousness [43]. Speculatively, different balances of these modes might correspond with different 'ways of experiencing' [53][54][55] (e.g., by characterising the difference between ordinary consciousness and altered consciousness during a psychedelic experience [60]). The recently proposed integrated information decomposition (ΦID), described next, provides a promising framework for exploring this idea. ...
Full-text available
The integrated information theory of consciousness (IIT) is divisive: while some believe it provides an unprecedentedly powerful approach to address the ‘hard problem’, others dismiss it on grounds that it is untestable. We argue that the appeal and applicability of IIT can be greatly widened if we distinguish two flavours of the theory: strong IIT, which identifies consciousness with specific properties associated with maxima of integrated information; and weak IIT, which tests pragmatic hypotheses relating aspects of consciousness to broader measures of information dynamics. We review challenges for strong IIT, explain how existing empirical findings are well explained by weak IIT without needing to commit to the entirety of strong IIT, and discuss the outlook for both flavours of IIT.
... While some popular accounts endorse the notion of the psychedelic state as an "expanded" (as opposed to diminished) state of consciousness, in reality psychedelics severely impair some aspects of human cognition and perception, while sparing or even facilitating others (Carter et al., 2005;Bouso et al., 2013;Bayne and Carter, 2018;Pokorny et al., 2020;Healy, 2021). Taking these considerations into account, several independent dimensions are likely to be required to fully characterize the repertoire of conscious states, yet disagreements exist about what these dimensions should be (Bayne et al., 2016;Bayne and Carter, 2018;Fortier-Davy and Millière, 2020). ...
Full-text available
Psychedelics are drugs capable of eliciting profound alterations in the subjective experience of the users, sometimes with long-lasting consequences. Because of this, psychedelic research tends to focus on human subjects, given their capacity to construct detailed narratives about the contents of their consciousness experiences. In spite of its relevance, the interaction between serotonergic psychedelics and language production is comparatively understudied in the recent literature. This review is focused on two aspects of this interaction: how the acute effects of psychedelic drugs impact on speech organization regardless of its semantic content, and how to characterize the subjective effects of psychedelic drugs by analyzing the semantic content of written retrospective reports. We show that the computational characterization of language production is capable of partially predicting the therapeutic outcome of individual experiences, relate the effects elicited by psychedelics with those associated with other altered states of consciousness, draw comparisons between the psychedelic state and the symptomatology of certain psychiatric disorders, and investigate the neurochemical profile and mechanism of action of different psychedelic drugs. We conclude that researchers studying psychedelics can considerably expand the range of their potential scientific conclusions by analyzing brief interviews obtained before, during and after the acute effects. Finally, we list a series of questions and open problems that should be addressed to further consolidate this approach.
Full-text available
Disorders of consciousness (DoCs) pose a significant clinical and ethical challenge because they allow for complex forms of conscious experience in patients where intentional behaviour and communication are highly limited or non-existent. There is a pressing need for brain-based assessments that can precisely and accurately characterize the conscious state of individual DoC patients. There has been an ongoing research effort to develop neural measures of consciousness. However, these measures are challenging to validate not only due to our lack of ground truth about consciousness in many DoC patients but also because there is an open ontological question about consciousness. There is a growing, well-supported view that consciousness is a multidimensional phenomenon that cannot be fully described in terms of the theoretical construct of hierarchical, easily ordered conscious levels. The multidimensional view of consciousness challenges the utility of levels-based neural measures in the context of DoC assessment. To examine how these measures may map onto consciousness as a multidimensional phenomenon, this article will investigate a range of studies where they have been applied in states other than DoC and where more is known about conscious experience. This comparative evidence suggests that measures of conscious level are more sensitive to some dimensions of consciousness than others and cannot be assumed to provide a straightforward hierarchical characterization of conscious states. Elevated levels of brain complexity, for example, are associated with conscious states characterized by a high degree of sensory richness and minimal attentional constraints, but are suboptimal for goal-directed behaviour and external responsiveness. Overall, this comparative analysis indicates that there are currently limitations to the use of these measures as tools to evaluate consciousness as a multidimensional phenomenon and that the relationship between these neural signatures and phenomenology requires closer scrutiny.
Full-text available
Serotonergic (or "classic") psychedelics have struck many researchers as raising significant philosophical questions that, until recently, were largely unexplored by academic philosophers. This paper provides an overview of four emerging lines of research at the intersection of academic philosophy and psychedelic science that have gained considerable traction in the last decade: selfless consciousness, psychedelic epistemology, psychedelic ethics, and spiritual/religious naturalism. In this paper, we highlight philosophical questions concerning (i) psychedelics, self-consciousness, and phenomenal consciousness, (ii) the epistemic profile of the psychedelic experience; (iii) ethical concerns about the appropriate use of psychedelics; and (iv) whether spiritual or religious dimensions of psychedelic use are compatible with a naturalistic worldview.
Full-text available
Studying transitions in and out of the altered state of consciousness caused by intravenous (IV) N,N-Dimethyltryptamine (DMT - a fast-acting tryptamine psychedelic) offers a safe and powerful means of advancing knowledge on the neurobiology of conscious states. Here we sought to investigate the effects of IV DMT on the power spectrum and signal diversity of human brain activity (6 female, 7 male) recorded via multivariate EEG, and plot relationships between subjective experience, brain activity and drug plasma concentrations across time. Compared with placebo, DMT markedly reduced oscillatory power in the alpha and beta bands and robustly increased spontaneous signal diversity. Time-referenced and neurophenomenological analyses revealed close relationships between changes in various aspects of subjective experience and changes in brain activity. Importantly, the emergence of oscillatory activity within the delta and theta frequency bands was found to correlate with the peak of the experience - particularly its eyes-closed visual component. These findings highlight marked changes in oscillatory activity and signal diversity with DMT that parallel broad and specific components of the subjective experience, thus advancing our understanding of the neurobiological underpinnings of immersive states of consciousness.
Full-text available
The main psychedelic component of magic mushrooms is psilocybin, which shows promise as a treatment for depression and other mental disorders. Psychedelic effects are believed to emerge through stimulation of serotonin 2A receptors (5-HT2ARs) by psilocybin’s active metabolite, psilocin. We here report for the first time the relationship between intensity of psychedelic effects, cerebral 5-HT2AR occupancy and plasma levels of psilocin in humans. Eight healthy volunteers underwent positron emission tomography (PET) scans with the 5-HT2AR agonist radioligand [11C]Cimbi-36: one at baseline and one or two additional scans on the same day after a single oral intake of psilocybin (3–30 mg). 5-HT2AR occupancy was calculated as the percent change in cerebral 5-HT2AR binding relative to baseline. Subjective psychedelic intensity and plasma psilocin levels were measured during the scans. Relations between subjective intensity, 5-HT2AR occupancy, and plasma psilocin levels were modeled using non-linear regression. Psilocybin intake resulted in dose-related 5-HT2AR occupancies up to 72%; plasma psilocin levels and 5-HT2AR occupancy conformed to a single-site binding model. Subjective intensity was correlated with both 5-HT2AR occupancy and psilocin levels as well as questionnaire scores. We report for the first time that intake of psilocybin leads to significant 5-HT2AR occupancy in the human brain, and that both psilocin plasma levels and 5-HT2AR occupancy are closely associated with subjective intensity ratings, strongly supporting that stimulation of 5-HT2AR is a key determinant for the psychedelic experience. Important for clinical studies, psilocin time-concentration curves varied but psilocin levels were closely associated with psychedelic experience.
Full-text available
Polycyclic aromatic compounds (PACs) are known due to their mutagenic activity. Among them, 2-nitrobenzanthrone (2-NBA) and 3-nitrobenzanthrone (3-NBA) are considered as two of the most potent mutagens found in atmospheric particles. In the present study 2-NBA, 3-NBA and selected PAHs and Nitro-PAHs were determined in fine particle samples (PM 2.5) collected in a bus station and an outdoor site. The fuel used by buses was a diesel-biodiesel (96:4) blend and light-duty vehicles run with any ethanol-to-gasoline proportion. The concentrations of 2-NBA and 3-NBA were, on average, under 14.8 µg g⁻¹ and 4.39 µg g⁻¹, respectively. In order to access the main sources and formation routes of these compounds, we performed ternary correlations and multivariate statistical analyses. The main sources for the studied compounds in the bus station were diesel/biodiesel exhaust followed by floor resuspension. In the coastal site, vehicular emission, photochemical formation and wood combustion were the main sources for 2-NBA and 3-NBA as well as the other PACs. Incremental lifetime cancer risk (ILCR) were calculated for both places, which presented low values, showing low cancer risk incidence although the ILCR values for the bus station were around 2.5 times higher than the ILCR from the coastal site.
Full-text available
It has often been suggested in the popular and academic literature that the psychedelic state qualifies as a higher state of consciousness relative to the state of normal waking awareness. This article subjects this proposal to critical scrutiny, focusing on the question of what it would mean for a state of consciousness to be ‘higher’. We begin by considering the contrast between conscious contents and conscious global states. We then review the changes in conscious global state associated with psychedelic drug use, focusing on the effects of two serotonergic hallucinogens: psilocybin and lysergic acid diethylamide. Limiting our review to findings obtained from lab-based experiments and reported in peer-reviewed journals, we prioritize the more common and reliably induced effects obtained through subjective questionnaires and psychophysical measures. The findings are grouped into three broad categories (sensory perception, cognitive function, and experiences of unity) and demonstrate that although certain aspects of consciousness are improved or enhanced in the psychedelic state, many of the functional capacities that are associated with consciousness are seriously compromised. Psychedelic-induced states of consciousness are indeed remarkable in many ways, but it is inappropriate to regard them as ‘higher’ states of consciousness. The fact that psychedelics affect different aspects of consciousness in fundamentally different ways provides evidence against the unidimensional (or ‘level-based’) view of consciousness, and instead provides strong support for a multidimensional conception of conscious states. The final section of the article considers the implications of this analysis for two prominent theories of consciousness: the Global Workspace Theory and Integrated Information Theory.
Full-text available
In recent years, the scientific study of meditation and psychedelic drugs has seen remarkable developments. The increased focus on meditation in cognitive neuroscience has led to a cross-cultural classification of standard meditation styles validated by functional and structural neuroanatomical data. Meanwhile, the renaissance of psychedelic research has shed light on the neurophysiology of altered states of consciousness induced by classical psychedelics, such as psilocybin and LSD, whose effects are mainly mediated by agonism of serotonin receptors. Few attempts have been made at bridging these two domains of inquiry, despite intriguing evidence of overlap between the phenomenology and neurophysiology of meditation practice and psychedelic states. In particular, many contemplative traditions explicitly aim at dissolving the sense of self by eliciting altered states of consciousness through meditation, while classical psychedelics are known to produce significant disruptions of self-consciousness, a phenomenon known as drug-induced ego dissolution. In this article, we discuss available evidence regarding convergences and differences between phenomenological and neurophysiological data on meditation practice and psychedelic drug-induced states, with a particular emphasis on alterations of self-experience. While both meditation and psychedelics may disrupt self-consciousness and underlying neural processes, we emphasize that neither meditation nor psychedelic states can be conceived as simple, uniform categories. Moreover, we suggest that there are important phenomenological differences even between conscious states described as experiences of self-loss. As a result, we propose that self-consciousness may be best construed as a multidimensional construct, and that “self-loss,” far from being an unequivocal phenomenon, can take several forms. Indeed, various aspects of self-consciousness, including narrative aspects linked to autobiographical memory, self-related thoughts and mental time travel, and embodied aspects rooted in multisensory processes, may be differently affected by psychedelics and meditation practices. Finally, we consider long-term outcomes of experiences of self-loss induced by meditation and psychedelics on individual traits and prosocial behavior. We call for caution regarding the problematic conflation of temporary states of self-loss with “selflessness” as a behavioral or social trait, although there is preliminary evidence that correlations between short-term experiences of self-loss and long-term trait alterations may exist.
Well-being, happiness, and quality of life are now established objects of social and medical research. Does this science produce knowledge that is properly about well-being? What sort of well-being? The definition and measurement of these objects rest on assumptions that are partly normative, partly empirical, and partly pragmatic, producing a great diversity of definitions depending on the project and the discipline. This book, written from the perspective of philosophy of science, formulates principles for the responsible production and interpretation of this diverse knowledge. Traditionally, a philosopher’s goal has been a single concept of well-being and a single theory about what it consists in. But for science this goal is both unlikely and unnecessary. Instead the promise and authority of the science depends on it focusing on the well-being of specific kinds of people in specific contexts. Sceptical arguments notwithstanding, this contextual well-being can be measured in a valid and credible way-but only if scientists broaden their methods to make room for normative considerations and address publicly and inclusively the value-based conflicts that inevitably arise when a measure of well-being is adopted. The science of well-being can be normative, empirical, and objective all at once, provided that we line up values to science and science to values.
This book focuses on the variability of metacognitive skills across cultures. Metacognition refers to the processes that enable agents to contextually control their first-order cognitive activity (e.g. perceiving, remembering, learning, or problem-solving) by monitoring them, i.e. assessing their likely success. It is involved in our daily observations, such as “I don’t remember where my keys are,” or “I understand your point.” These assessments may rely either on specialized feelings (e.g. the felt fluency involved in distinguishing familiar from new environments, informative from repetitive messages, difficult from easy cognitive tasks) or on folk theories about one’s own mental abilities. Variable and universal features associated with these dimensions are documented, using anthropological, linguistic, neuroscientific, and psychological evidence. Among the universal cross-cultural aspects of metacognition, children are found to be more sensitive to their own ignorance than to that of others, adults have an intuitive understanding of what counts as knowledge, and speakers are sensitive to the reliability of informational sources (independently of the way the information is linguistically expressed). On the other hand, an agent’s decisions to allocate effort, motivation to learn, and sense of being right or wrong in perceptions and memories (and other cognitive tasks) are shown to depend on specific transmitted goals, norms, and values. Metacognitive variability is seen to be modulated (among other factors) by variation in attention patterns (analytic or holistic), self-concepts (independent or interdependent), agentive properties (autonomous or heteronomous), childrearing style (individual or collective), and modes of learning (observational or pedagogical). New domains of metacognitive variability are studied, such as those generated by metacognition-oriented embodied practices (present in rituals and religious worship) and by culture-specific lay theories about subjective uncertainty and knowledge regarding natural or supernatural entities.
Hallucinations possess two main components: (i) a sensory content; (ii) a sense that the sensory content is real. Influential models of schizophrenic hallucination claim that both the sensory content and the sense of reality can be explained in terms of metacognitive dysfunction. This chapter assesses whether such a claim holds for schizophrenic and drug-induced hallucinations; it further attempts to determine the actual role of metacognition in hallucination and how this role is liable to vary across cultures. It is first argued that the notion of sense of reality is heterogeneous and should therefore be divided into distinct kinds. Next, some monitoring-based models of hallucination are presented, and it is shown that they fail to explain important aspects of hallucinations. It is subsequently suggested that the main mechanisms of serotoninergic hallucinogens are not metacognitive, whereas those of anticholinergic hallucinogens importantly tap into subpersonal metacognitive processes. Finally, after specific consideration of the use of ayahuasca across different Amazonian indigenous groups, it is proposed that the metacognitive properties of hallucinogenic experiences can be variously exploited or ignored depending on cultural expectations.