Pattern Breaking: A Complex Systems Approach to Psychedelic Medicine
This theory-building article (2022) further refines the REBUS model, using complex systems theory (CST) to propose that psychedelics act as destabilisers of stuck patterns of thinking ('attractors' or 'overweighted priors') which could explain both the acute (peak) and subsequent period in which psychedelics can help one get 'unstuck'.
Abstract
There is growing evidence for the safety and efficacy of psychedelic therapy in mental health care. What is less understood however, is how psychedelics act to yield therapeutic results. In this paper we propose that psychedelics act as destabilisers - both in a psychological and a neurophysiological sense. Our proposed framework builds on the ‘entropic brain’ hypothesis, according to which psychedelics increase the entropy of spontaneous cortical activity and, in parallel, the richness or depth of content of psychological experience. The so-called ‘RElaxed Beliefs Under pSychedelics’ (REBUS) model is a predictive-coding inspired extension to this hypothesis, which states that psychedelics’ entropic action is paralleled by a relaxation of prior assumptions. Here we adopt a complex systems theory (CST) perspective, proposing that psychedelics act as destabilisers of excessively reinforced fixed points - or ‘attractors’ - which translates as the breaking of excessively reinforced or overweighted patterns of thinking or behaving. Our CST approach explains how psychedelic-induced increases in brain entropy destabilise neurophysiological set-points that are synonymous with overweighted priors, thereby augmenting and enriching the account given by REBUS. We believe that this perspective helps inspire conceptualisations of psychedelic psychotherapy - bearing relevance both to the peak psychedelic experience and subsequent sub-acute period of potential recovery. We discuss implications for risk mitigation and treatment optimization in psychedelic medicine.
Research Summary of 'Pattern Breaking: A Complex Systems Approach to Psychedelic Medicine'
Introduction
Hipólito and colleagues frame the paper around the growing clinical interest in psychedelic-assisted therapy and the parallel need to understand mechanisms that produce enduring therapeutic benefit. The authors note that psychedelics show promise across several psychiatric indications (including treatment-resistant depression, suicidality in terminal illness, PTSD, OCD and eating disorders) and that subjective features of the acute experience strongly predict clinical outcomes. They argue for the importance of integrating psychological and biological accounts: psychological sophistication and psychotherapeutic support appear necessary for durable gains, while a clearer neurobiological model could help validate therapeutic effects and mitigate risks of misapplication. To address explanatory gaps the paper proposes a synthesis that brings together the entropic brain hypothesis and the predictive‑coding inspired REBUS model with tools from Complex Systems Theory (CST). The central claim is that psychedelics act as destabilisers—increasing neural and experiential entropy and thereby weakening excessively reinforced ‘‘attractors’’ or set‑points in brain–mind dynamics. This destabilisation, paired with appropriate integration, offers an opportunity for reconfiguring maladaptive patterns of cognition and behaviour that underpin psychopathology. The authors present this as a theoretical, cross‑scale framework with implications for safety, therapeutic optimisation and empirical measurement.
Methods
This paper is a conceptual and integrative review rather than a primary empirical study. The investigators synthesise findings and theoretical constructs from cognitive neuroscience (entropic brain, REBUS, free‑energy principle), complexity science (dynamical systems, attractors, criticality), and philosophical psychology (enactivism, relational/contextual perspectives). The extracted text does not report a formal systematic search strategy, inclusion/exclusion criteria, or quantitative meta‑analytic methods; therefore, it should be read as a theoretical synthesis drawing on a range of empirical and theoretical sources cited by the authors. Analytically, the authors map established empirical observations (e.g. increased measures of brain entropy under psychedelics, changes in hierarchical brain organisation, EEG correlates, and psychological predictors of outcome) onto CST concepts such as attractors, phase transitions and self‑organised criticality. They also incorporate psychological constructs (e.g. rumination, emotional breakthrough, tolerance of uncertainty) and clinical practice elements (set, setting, preparation, integration) to propose mechanistic links across scales from neurophysiology to social context. Where measurement is discussed, the paper highlights complexity metrics (for instance Lempel‑Ziv compressibility) and existing subjective scales (e.g. Altered States of Consciousness, Emotional Breakthrough Inventory, Psychological Insight Scale) as candidate indices to test the framework.
Results
Rather than reporting novel empirical data, the authors present a series of interrelated claims supported by previously published findings and theoretical reasoning. Key reported points are: psychedelics reliably increase metrics of spontaneous cortical entropy and diversity of neural dynamics, an effect especially evident in the cortex and measurable with techniques including EEG and imaging; increased neural entropy parallels a richer, more complex phenomenological state. Within the predictive‑coding/Free Energy Principle framework, these entropy increases are linked to a reduction in precision weighting of high‑level priors (the REBUS hypothesis), which permits escape from overly reinforced local optima in the brain’s dynamical landscape. Translating these neurophysiological effects into psychological terms, the authors argue that psychopathology can be modelled as excessively deep or rigid ‘‘attractors’’—stuck states such as rumination, compulsivity, addiction and other repetitive patterns. Psychedelics, by injecting ‘‘temperature’’ or noise and flattening basins of attraction, can destabilise these pathological attractors and increase the system’s repertoire of accessible states, potentially facilitating learning and behavioural change. The text cites empirical parallels: observations of flattened brain energy landscapes, reduced hierarchical gradients, disrupted Bayesian inference metrics, and psychometric findings linking intensity or qualities of acute experience (e.g. emotional breakthrough, mystical‑type experience) with subsequent clinical improvement. The authors also note boundaries and caveats reported in the literature: cognitive performance effects are dose‑dependent and can flip from enhancement to impairment; increased sensitivity to context can produce therapeutic amplification but also heighten risk if psychosocial support is poor; documented adverse outcomes include instances of iatrogenic harm such as boundary violations and ‘‘false memory’’ concerns when integration or therapist training are inadequate. Finally, the authors identify candidate measurable signatures for the proposed processes (brain entropy metrics, criticality markers such as long‑range correlations and critical slowing down, and subjective scales of experience) and emphasise the role of integration and behavioural change following destabilisation for weakening old attractors through extinction and re‑reinforcement of healthier patterns.
Discussion
The discussion positions Complex Systems Theory as a unifying language that respects phenomenology while linking brain, mind and social dynamics. Hipólito and colleagues argue that CST complements the REBUS/entropic brain account by offering a dynamical vocabulary—attractors, phase transitions, criticality—to describe how psychedelics might enable topological reconfiguration of brain–mind state spaces. From this perspective, mental health corresponds to a well‑nested, harmonically organised set of state dynamics across levels (neural, bodily, interpersonal), whereas psychopathology reflects excessively narrow or deep attractor basins that reduce behavioural flexibility. The authors acknowledge limitations and uncertainties in their proposal. They describe the CST‑framed model as conceptually promising but ‘‘loose in detail’’ and in need of focused empirical testing, including validation of candidate neurophysiological markers (e.g. measures of entropy and complexity) as predictors of therapeutic outcome. Practical implications discussed include the necessity of integrating psychedelic administration with high‑quality psychological support to capitalise on destabilisation while minimising risks; the importance of therapist training and monitoring to avoid suggestion, undue priming or boundary violations; and caution regarding dose, individual sensitivity and adverse set/setting. The discussion closes by proposing that further empirical work should test the model’s claims and explore the hypothesised links between destabilisation, criticality markers, experiential measures and durable clinical change.
Conclusion
Hipólito and colleagues conclude that psychedelics are plausibly understood as destabilisers operating at neurophysiological and psychological levels, increasing cortical entropy and enriching conscious content while relaxing overweighted priors. Framed within Complex Systems Theory, this destabilisation provides an opportunity to dismantle excessively reinforced attractors that underlie psychopathology, enabling topological reconfiguration of the mind–brain landscape. The authors emphasise that such drug‑induced destabilisation is most likely to produce sustained benefit when paired with appropriate psychological preparation and post‑dosing integration, and they call for empirical work to refine and test the CST‑based model. The extracted conclusion appears to be truncated in the provided text, so any final remarks that follow "We end with" are not available in the extraction.
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INTRODUCTION
The wider acceptance and de-stigmatisation of psychedelicsis allowing researchers to investigate their potential for the treatment of psychopathology. A growing amount of experimental evidence suggests that psychedelics could eventually become a breakthrough new treatment paradigm in psychiatric, social, and palliative care, although the approach is not without risks or critique. One important property of psychedelics is their low addictive properties and other physical side-effects. This feature gives them an advantage over several currently approved drug treatments in mental health care. Recent evidence suggests that psychedelic therapy may lead to significant and sustained antidepressant and anxiolytic effects, even for individuals with treatment-resistant depression. Good results have also been seen in cases with high suicidalityand psychological distress linked to terminal illness. Psychedelic therapy could also yield important treatment gains in cases of PTSDand eating conditions, Obsessive Compulsive Disorder (OCD)) as well as other common mental health conditions. There is a wealth of evidence that the quality of the acute psychedelic experience is predictive of subsequent mental health improvements; suggesting that the subjective effects of psychedelics may be necessary for enduring therapeutic outcomes. Indeed, psychedelics often trigger experiences that many subjects regard as being insightful and replete with meaning. In this sense, therapeutic progress via psychedelics is epistemic or learning-based, which could explain why it can endure -as well as what fails when it does not. This epistemic quality to psychedelic medicine arguably underlines the importance of meeting it with a psychological sophistication, including skilful and sufficient psychotherapeutic support. While we recognise the importance of understanding psychedelics through a psychological lense, and applying them with expert psychological know-how, we equally value the importance of a biological comprehension of their action. Indeed, a thorough biological understanding of psychedelics could help mitigate risks of their mis-application -as well as fallacious philosophical assumptions, such as that they do not have a principal action on brain function. Moreover, solving uncertainties regarding the biological action of psychedelics could help validate their medicinal action and value e.g., by demonstrating that the positive clinical outcomes observed in recent trials are more than a mere placebo-type response. The present paper takes inspiration from Complex Systems Theory (CST), which lends itself well to both psychological and neurological descriptions of phenomena due to appeal to fundamental, shared mechanisms, at the appropriate dynamical systems level. Accordingly, we argue that psychedelics act as destabilisers both in an experiential and neurophysiological sense, acting on set-points or 'attractors' i.e., system-level sub-states with gravitational pull, that become stereotyped in psychopathology, through repetition and reinforcement. We show that the de-stabilisation of such '(re)functional' set-points is key to the potential therapeutic action of psychedelic therapy but also relates to risks associated with psychedelics, if abused or mis-applied.
NEUROSCIENCE OF PSYCHEDELICS: PSYCHEDELICS AS DESTABILISERS ON THE
Neuro-physiological Level "It is proposed that psychedelics work by dismantling reinforced patterns of negative thought and behaviour by breaking down the stable spatiotemporal patterns of brain activity upon which they rest". The treatment effect of psychedelics has often been described in reference to the destabilisation or disruption of globally distributed brain dynamics. Empirically, this idea is inspired by findings showing that the psychedelic experience coincides with an increase of entropy in properties of spontaneous brain activity, an effect that is likely to be most pronounced in the cortex. Entropy, in its purest informational sense, is a dimensionless metric that captures the unpredictability or randomness of a dynamical phenomenon such as a time series. Applied to the brain, an increase in entropy may indicate that neuronal circuits are exploring a wider array of patterns of activity, with potential departures from normal repertoire of states. The principle that brain entropy increases under psychedelics has been supported by a large number of empirical findingsand moreover, the principle that brain entropy tracks a principal dimension of conscious experience, is increasingly well supported -now well beyond just research with psychedelics. When we look at the brain as a hierarchical prediction engine -e.g., as one does under the so-called 'Free Energy Principle' (FEP), an increase in the entropy of spontaneous brain activity can be related to a decrease in the precision weighting -or the stability or reliability -of prior assumptions. Indeed, this is what is proposed in the so-called relaxed beliefs under psychedelics (REBUS) modela unifying theory of the brain and psychological action of psychedelic compounds that bears relevance to their therapeutic potential. According to the Free Energy Principle and the 'active inference' component that it subsumes, the brain and behaviour (self) organises, or is volitionally organised, to minimise surprising encounters in the world by maximising the reach, reliability and efficiency of its internal models and behavioural schemas, in a fashion that is consistent with Hamilton's principle of 'least action'. Building on this, the REBUS model proposes that the entropy-enhancing action of psychedelics works against this imperative -i.e., psychedelics flatten the dynamical global landscape of brain states, allowing for an easier escape from local optima, including ones that may have become excessively reinforced in pathology, but also creating a basal sense of felt uncertainty as the content of consciousness becomes unpredictable and 'enriched' relative to normal waking consciousness. This principle has been supported by recent experimental work on the acute action of psychedelics -finding a flattening of the brain's energy landscape, as well as the collapse of brain principal hierarchical gradient, and the disruption of processes of Bayesian inference. Electroencephalography work has also substantiated the close relationship between brain entropy and the felt 'richness' of conscious experience. In the domain of perception, the downregulation of precision weighting on priors -as postulated by the REBUS model -will have various predictable effects, such as causing the instability of otherwise stable top-down percepts. One might also hypothesise that so-called 'learning traps' and associated cognitive misadjustments may be impacted by psychedelics in a potentially useful way, potentially yielding performance benefits -similar to those that have been observed in children's healthy learning flexibility. Evidence of increased learning rate under LSD) and sub-acute cognitive flexibility after psychedelics) may be relevant in this regard. However, we wish to caution that performance may be vulnerable to generalised deficit confounds under psychedelics, meaning that any hypothesised performance enhancement is likely to be dose-dependent (i.e. establishing the right dosage for a specific case), 'topping-out' into non-specific deficits above a certain dose range -e.g., seefor evidence of decreased cognitive flexibility under the acute effects of a psychedelic. Overall, the REBUS model integrates the entropic brain hypothesis and the free-energy principle framework. Central to this integration is that the entropic brain and the free energy principle interrelate in that they share the notion of entropy as a dimensionless measure of uncertainty that can be applied to brain, mind and behaviour as complex dynamical phenomena. The REBUS model has been supported by a number of empirical findings. Firstly, there is now substantial evidence to support the entropy brain principle, in terms of increased brain entropy in relation to the psychedelic state, and other flexible mental states such as Rapid Eyes Movement Sleepand dreaming, jazz improvisation, and deep meditation-and reduced brain entropy under states of reduced consciousness such as deep sleep, the anaesthetized stateand disorders of consciousness. More specific support for REBUS can be found in perceptual changes under psychedelics, altered beliefs underand after psychedelicsas well as other trait changesas well as decreased top-down processing seen through such metrics as travelling waves, dynamic causal modelling, and transfer entropyreduced hierarchical organisation under psychedelics) and the flattening of the brain's energy landscape under) and afterpsychedelics. Above, we have briefly summarised how an increase in the entropy of spontaneous cortical activity during the psychedelic state can be understood from an empirical and computational framework. In this paper, we will leverage these dynamical aspects to model the effect that psychedelics have on the psychological domain using dynamical/complex systems theory.
PHILOSOPHICAL PSYCHOLOGY: PSYCHOLOGICAL PHENOMENA?
There is growing evidence that psychedelics can have a positive impact on mental health, particularly when applied as psychedelic-assisted therapy. There is also robust and reliable evidence that the subjective effects of psychedelics are predictive of their enduring therapeutic effects. Future work is required to test whether these subjective effects are paralleled by tightly coupled and equally predictive brain activity markers. We also hypothesise that the entropy or complexity of spontaneous cortical activity, such can be indexed by metrics such as Lempel-Ziv complexity or other compressibility algorithms, will emerge as valuable explanatory and predictive markers of action. We believe that such discoveries will lend support to a unified model of the potential therapeutic action of psychedelics that places emphasis on an acute entropic brain action and related relaxation of assumptions (i.e., the REBUS model) -yielding an opportunity for the revision of pathologically reinforced patterns of cognition and/or behaviour underpinning symptoms of psychiatric illness.. In the present work, in keeping with a biopsychosocial approach to medicine, we wish to give an appropriate level of attention to psychosocial factors relevant to the psychedelic experience In this regard, we adopt a relational and context sensitive and dependent approach, whereby we see individual experiences as coloured by personal historical and sociocultural factors). This perspective is consistent with the philosophical psychology of Ludwig Wittgenstein as well as recent accounts of enactivism and ecological psychologythat aim to situate the cultural and personal significance of experiences, emotions and behaviours. According to this view, psychological objects or events have no absolute truth conditions but rather, exist in a web of relations or mutual inter-dependencies. The goal and approach of many psychotherapies is not to make difficult memories or emotions 'disappear' but rather, to place them in a perspective whereby they can be better contextualised and understood e.g., with greater equanimity. So called 'third wave' psychotherapies such as acceptance and commitment therapy (ACT) and mindfulness-based cognitive therapy (MBCT) place particular emphasis on allowing for the expression and mindful awareness of negative feeling states, as a method for processing and, ideally, dissipating their influence. It could be said that the aim of these and other psychotherapeutic approaches is to replace 'unhealthy' patterns of thinking and behaving with 'healthier' ones, where what determines the 'health' of a cognitive style or behaviour rests on its embeddedness within a complex network of largely consensual norms and values e.g., that view drug addiction, suicidal intent, chronic under-eating or compulsive hand-washing as dysfunctional in relation to these norms and values. Conversational psychotherapy can seek to better align a patient's cognition and behaviour with societal norms and values but this process is slow and difficult and may be even more effectively achieved if the patient discovers their own desire for better alignment or 'connectedness') through a transformative experience and an epistemic process of self-realisation -such as can occur via psychedelic therapy). In the next section, we formulate psychopathology in relation to dynamical, complex systems theory, a level and approach that we feel can help identify heuristically appealing equivalences between phenomenology and brain dynamics.
COMPLEXITY SCIENCE: ESSENTIAL TERMINOLOGY
A complex system is a system whose behaviour results from a highly non-trivial aggregation of interactions, both between the parts of the system and also between the system and its environment. Systems are complex to the extent that these relationships involve multi-scales, complex external influences, nonlinearity, feedback loops, and multiplicity, which, in turn, may give rise to self-organisation and emergent phenomena. Complex systems theory (CST) 2 is an interdisciplinary research programme that aims to understand the underlying common features of complex systems that arise in different levels of nature -from physics, chemistry and biology to sociology, economics and art -by studying them with a range of tools including statistical physics, information theory, and nonlinear dynamics, systems theory, self-organisation, nonlinear systems, and network theory (see Fig.). The complex world is both directly accessible and hidden. It is directly accessible in that we can, in many ways, perceive and measure some aspect of it; and yet, it is hidden behind near infinite multi-scale complexity and granularity, nonlinearity, randomness, collective dynamics, hierarchy, and emergence.
FIGURE 1. COMPLEXITY SCIENCE IS COMPOSED OF AN ARRAYOF DIFFERENT TECHNIQUES, WHICH TOGETHER AIM TO CAPTURE THE UNIFYING COMMON FEATURES OF THE BEHAVIOUR OF MULTI-SYSTEM INTERACTIONS.
For reasons not yet entirely understood, complex physical systems and biological processes can self-organise without external direction or control e.g., via an outside or centralised system. This is a particular feature of complex living systems, and when it occurs, such systems attain states of "spontaneous" order which seem to defy the second-law of thermodynamics -i.e., the natural tendency for structures to degrade, dissipate or die. Self-organisation typically occurs within complex non-equilibrium systems, i.e. 2 CST is an interdisciplinary research programme that aims to understand the unifying features of complex systems that arise in different fields of science, including meteorology, sociology, economics, philosophy, psychology, and biology. For this purpose, CST leverages methods of different disciplines including statistical physics, information theory, nonlinear dynamics, anthropology, and computer science. systems that are not thermodynamically relaxed, but rather are subject to regular, complex interactions between and within their parts, and between the system and complex external influences i.e., their 'environment' s. Theories of self-organisation try to explain how different systems naturally tend towards distinctive types of intrinsic dynamical organisation. One leading theoretical approach to self-organisation is the notion of "self-organised criticality", which studies how dynamical systems spontaneously tend towards distinct recurring patterns or states i.e., attractors. As the name implies, self-organised criticality is often found close to a phase transition (or 'critical point' or zone) beyond which the system degrades into disorder or randomnessi.e., high entropy. Thus, critical systems can be viewed as exhibiting a functionally useful balance between self-maintenance and adaptability. In a poetic sense, they surf uncertaintyor entropy. Complex systems can be studied as dynamical to the extent that a Dynamical Systems Theory (DST) toolbox is used to make sense of transitions in their trajectories and patterns of behaviour. A system's evolution can be mapped as a trajectory in time, which illustrates a system's behaviour. The trajectory shows this behaviour as tending to fixed stable or semi-stable points, known as attractors, and avoiding fixed unstable points, known as repellers. The future state of a complex system is generated by its current state in interaction with its external environment, which can be cast under a dynamical rule. The case of a more complex system such as an adaptive system entails a more complex geometry of fixed points. Studying an adaptive system's behaviour can help us to gain insight into its function, such as how the system adapts in relation to changing environmental circumstances. Studying this can inform on the system's features or properties, such as its nonlinearities and interdependencies. The emergent complexity of a complex system arises precisely from the consequences of nonlinearities in the dynamics of the interacting subsystems, which are reflected in patterns of interactions among them at various timescales. One approach to conceptualise the complexity of a system is by how difficult it is to model a resulting behaviour. Modelling approaches that fail to acknowledge complexity -for example by reducing complexity to linear processes -will necessarily generate models that are not explanatory nor epistemically useful. This is particularly important when planning interventions, e.g.,. a too simple model could cause us to intervene in a way that obtains an opposite effect from the one originally intended. This is crucially important for mental health interventions, as we develop in the following sections. Sudden transitions can have a huge, potentially irreversible impact on a complex systemsuch as global changes in climate, shifts in ecosystems, crashing in financial markets, sudden iatrogenic transitions in one's psychological status, e.g., into a psychotic or depressive episode. Some sudden transitions can be described as 'tippings'. These can occur when tiny changes to one or more of the system's parameters lead to deep qualitative changes in the state of the global system. In non-resilient complex systems, tipping in one subsystem can result in tipping cascades and turbulence in the whole system. Interestingly, tipping and cascading may not necessarily have detrimental effects, e.g., if these phenomena can be planned for and harnessed for functional purposes, such as large scale information transfer or functionally useful global system transformationsThe prediction of tipping can be useful for preventing, preparing for, or controlling their occurrence or consequences. Tipping can be induced in complex systems by intentional perturbations such as 'temperature' increases, causing bifurcations, fluctuations or noise near critical states and rate-dependent variations of drift in control parameters of the dynamics. Some of the points identified as critical for typing cascades include
PSYCHOPATHOLOGY FROM A COMPLEXITY SCIENCE PERSPECTIVE
Here we apply a complexity theory approach to our understanding of psychopathology. As already stated, CST lends itself well to bridging phenomenology and psychopathology as it arguably approaches both at a functionally meaningful mechanistic level, where natural mappings between brain and experience can be made. We seek to bring CST to psychopathology by focusing on three main components: the emergence from a wholeness, a specific pattern or order, and the notion of "stuck" states. To address the challenges of recovering from the latter, psychotherapeutic intervention can be thought of as aiding recovery via intentionally causing an initial and arguably vital destabilisation. Indeed, empirical evidence for the value of destabilisation in the therapeutic process already exists, and the theme of 'sudden gains' in psychotherapy is also relevant here. When studied from a complexity theory perspective, psychopathology can be seen as a specific type of dynamic pattern emerging from self-organising interactions involving various biological, social and psychological components of an adaptive system and its environment. According to our perspective, psychopathology cannot be properly understood by decoupling the individual from his/her environment. Moreover, psychopathology is seen as an emergent phenomenon, in the sense that it depends on the coupling between the individual and his/her environment, and hence it cannot be reduced to the sum of the parts in isolation). Thus, we see psychopathology as a dynamic process, a self-organised pattern that arises from a specific type of interdependence between biopsychosocial components. This implies that psychopathology cannot be properly understood by isolating separate contributions of parts of the system, but has to be understood and treated as a whole. Understanding patients and psychopathology as complex "wholes" means advancing an explanation that unifies the various scales that constitute the whole, which includes the psychological experience situated in a sociocultural setting. Seeing psychopathology from the lens of complexity science also lends support to the controversial position that symptoms of mental illness should not necessarily be seen reflective of a discrete disorder per se, rather they may be seen as reflective of a different kind of order, i.e., an effective 'next best' order when, for quite logical and rational reasons, circumstances do not allow for a 'healthy' order, as it is generally understood. Here we use 're-order' and 're-ordering' to refer to the abnormal but not necessarily 'dysfunctional' order that underlies symptoms of mental illness. Thus, from this arguably more human and empathic perspective, psychopathology corresponds to a peculiar type of reordering that arises when specific patterns form within a complex dynamical process. Hence, while still being regarded as a mental health condition or disease, psychopathology is not seen as a disorder disrupting an otherwise healthy pattern -such as an imbalance in individual parts, i.e. neurotransmitters, hormones, or personality traits, but as a dynamical pattern itself -which is to say, it is a kind of order that is distinct from the dynamical patterns that we typically associate with the absence of a certain mental condition i.e., 'health'. This dynamical view of psychopathology can be further developed following an enactive approachoperationalised via tools from dynamical systems theory. In this framework individuals are seen as evolving coupled with their sociocultural environment, viz. enacting their environment, which can be interpreted as a dynamical process whereby a system traverses a given "phase space" -i.e. the set of possible states or configurations available to the individual. In enacting their environments, the specific properties of how the individual is presently coupled with its environment results in the dynamical trajectory being more or less attracted to certain behaviours, represented by the system persisting on different regions of the phase space. Dynamical systems theory then tells us that such attractor sets can be of different types: single stable points, periodic cycles, or so-called "strange" attractors of complicated geometries. Moreover, a given system can have multiple attractors and dynamically switch between them, which give rise to metastable behaviour -which has been shown to be important for biological and social systems. The ways in which an individual navigates the geometry of its attractors determines its behaviour, which in turn feeds back into its environment and determines the future dynamical geometry that it will observe. This process can introduce bifurcations (i.e. the rupture of one attractor into two separate attractors) or more general dynamical phase transitions in which qualitative changes alter the attractor landscape, which characterise important processes of change in living systems. Emotional states themselves can be seen as attractors -e.g. sadness can be seen as a fixed-point attractor that, depending on how the individual is coupled with its environment, might exert more or less influence over an individual's trajectories. Importantly, biological beings are a consequence of their actions, which implies that -all coupling conditions remaining equal -the more the system visits that attractor point, the more the system will be likely to visit it again. This process is consistent with experience dependent plasticity and reinforcement learning. Individuals can also develop cycle attractors, e.g. becoming stuck in periodic shifts between being melancholic and euphoric -such as occurs in bipolar disorder (for illustration of these states as attactors, see figure). Importantly, such experience-dependent reinforcement is the process by which attractors deepen, a process commensurate with increasing the precision weighting on priors, if cast in a manner that is consistent with the free-energy principle and its use of predictive coding and the Bayesian brain. Indeed, this is the re-ordering process that we argue lies at the heart of the development and perpetuation of symptoms of mental illness, i.e. the brain and behaviour continues to adhere to the free-energy principle but uses a different, 'abnormal' strategy for achieving the minimization of uncertainty. Figure. A depiction of how a system's state (represented in orange) evolve with a tendency towards certain "attracting" points (green boxes). Importantly, the same attractors can exert a stronger or weaker influence over a system, represented here by the depth of the valley -the deeper it is, the harder it is to go away from it and the easier it is to fall into it and become stuck. Psychedelics may flatten the attractor landscape (e.g. move from deep valleys in black to shallow valleys in blue), increasing the probability of the system's state to move between attractors and hence promoting more flexible, adaptive, and meta-stable dynamics. Biological systems are always subject to 'noise' -i.e., random or apparently random complex perturbations, either from internal or external sources -that introduces small fluctuations in the system's dynamics; however, attractor states represent favoured states that the system tends to stabilise into. In principle, this property of attractors imbues biological systems with a robustness or resilience, but it can become problematic when the attractor becomes too reinforced or rigid -e.g., aligning with cognitions or behaviours that clash with societal norms and values -such as it the case with most symptoms of psychiatric illness. The paradox of stable attractor states is that they can provide a rewarding and attractive low level of uncertainty e.g., by finding solace in the effects of a drug of addiction or the apparent 'safety' of a 'dark room' of depression. However, a too stable attractor or 'stuck state' affords reduced degrees of freedom, i.e., fewer possibilities for other forms of thought or action. It therefore affords a 'narrower' state of being. Here, we argue that this stereotypy, closely linked to excessive precision weighting on priors, in a free-energy framework, or excessive experience dependent plasticity and reinforcement learning, is the first component of mental illness, qualified to some extent, by whether the relevant stereotypy is at odds with the norms and values of a given society or culture. By this we mean that an 'expert' who has developed his/her experience-dependent expertise through extensive practice does not necessarily exhibit psychopathology i.e., because their expertise is valued by a given culture or society.. An example of a common 'stuck state' -that is often regarded as pathological -is rumination. Rumination involves repetitive or stereotyped patterns of thinking that features a pull toward a thematic core that is difficult to escape from. Although rumination begins with a desire to resolve a psychological issue -i.e. to examine, make sense, or learn from a social dilemma, major surprise or trauma-it can easily turn into a psychopathological condition (as defined above). For example, one can easily imagine a scenario where what might have started as an attempt to understand or resolve a past action/event ("why didn't I yell more loudly?', 'it was my fault for driving on the freeway in heavy rain') leads to a stuck state ("I'll never get over this; I'll never live a normal life again"). In depression, patients often continually ruminate about their failings, reiterate thoughts of guilt, and engage in self-critical inner narratives. In addiction, drug craving drives behaviour that is specific, narrow, and rigid; individuals with addiction ruminate on their preferred substance(s) of abuse: why they can't get away from it, where they need to go or what they need to do to get it and pay for it etc. In obsessive-compulsive disorder and anorexia, there is excessive rumination about threats to the person, i.e. the effects of eating or overeating. As with addiction, ancillary behaviours such as paying for drugs via prostitution or binge-purging in eating disorders, can work to further reinforce the disorder through repeated and reinforced feelings such as shame. Similarly, although often inadvertently, interpersonal relations can shape around the illness, creating a psychosocial matrix of continued reinforcement e.g., living among fellow drug addicts. Following the ideas exposed above, psychopathology is better understood not by the nature of the beliefs supporting given thoughts or behaviours but by the weight they are given, i.e., in a free-energy sense, the problem lies more with the precision-weighting of priors than whether they are 'false' or not; although, granted, excessive precision-weighting can overly reinforce certain beliefs that then appear 'false', or at least overgeneralized. Thus, in a CST sense, the problem lies not with what an attractor encodes, but with its depth or steepness of attraction i.e., the relative difficulty if not apparent 'impossibility' of moving away from the state. Said another way, the illness rests not with the content of specific states, but with their inter-relations and dynamics. For example, it is reasonable and healthy that certain events should cause stress and/or anxiety but healthy systems and individuals are able to bounce back from these stressors rather than become pulled into a web of mutually reinforcing thoughts, actions and relations. According to our scheme, psychopathology is the excessive difficulty of moving away from a state or states, i.e being in a stuck state that clashes with the norms and values of a given society or culture and does not allow for the psychological freedom that is the sine qua non of health. Stuck states are closely related to how agents deal with uncertainty. Following the Free Energy Principle, one can operationalise surprise 3 as the difference between an agent's assumptions about the world and the world they actually encounter. Agents adapt to their environments in the ways they adjust to surprising events -including whether they can "bounce back" from such surprises. Typically, as mandated by the free-energy principle, one recalibrates from a surprising event by updating one's assumptions or by altering one's behaviour -or world itself, such that surprises are less likely. However, agents do not simply find a dark corner and stay there -what is known as the "dark room" problem,but minimise surprise within a longer, more far-sighted time horizon) which usually leads them to act in specific ways. When confronted with a surprising event, an agent has at least two options: either (1) to tend towards a stuck state or (2) to reduce its surprise by adapting to the environment. An agent tending towards a "stuck state" can be seen as potentially entering a phase transition towards a psychopathological situation, or a dark room. Some environments lead to more surprising events than others; for example, militars often experience events with high levels of surprise while having few forms of action for reducing it, and thereby adapting to the environment. From a psychopathology point of view, this means that it is likely that, faced with prolonged high levels of surprise, an agent will be "stuck" in that state, even after being removed from that environment -a psychological condition that may be associated with PTSD. Lastly, a third strategy for dealing with surprise is to tolerate a high amount of it. The so-called 'tolerance of uncertainty' trait, is a useful construct in this regard, where a high tolerance of uncertainty may be conducive to resilience and thus, good psychological healthas has been shown. Here, one might surmise that the agent employs an especially broad time horizon for the minimization of free-energy, i.e. by accepting a higher than average level of uncertainty they may more easily explore and thus broaden their models of the world and self, which they then 'hold lightly'-as they recognize they may not apply absolutely. One might connect this broad, patient and flexible style of free-energy minimization and 'light belief ' with Buddhist philosophy and practice as well as third wave psychotherapies, such as ACT. Indeed, this explains the contention that Buddhist practiceand third wave cognitive-behavioural therapies may be a particularly 'good fit' for psychedelic-assisted therapy, as well as the view that a combination of psychedelic drug administration and evidence-based psychological therapy is most beneficial, if not essential for reliable positive outcomes. Meditation practices are known for their effectiveness in cultivating compassion, acceptance and self-awareness. With professional guidance, meditation may be a useful supplement to the psychological integration process. Indeed, as we shall discuss below, integration is considered by many to be a critical component of safe and effective psychedelic therapy, safe-guarding against the risks associated with psychological destabilisation and exploiting its potential benefits. Taking inspiration from psychedelic therapy, here we argue that in order to confront the possibility of entering a stuck state rather than bouncing back from adversity, or the actuality of having fallen into such a stuck state -and now needing to get out of it -a therapeutic intervention requires the induction of destabilisation. Destabilisation is hence defined as the induction of a dynamical phase transition involving either or both: 1) more energy or 'temperature' in the system to drive more random fluctuations -commensurate with higher entropy, or 2) the lowering of steep basins of attraction. We argue that the first process (i.e. a temperature or entropy increase) is the most accessible and manipulable, whereas the latter arguably requires more time, i.e. the longer the agent is away from an old attracting state or visiting others, the weaker the old attracting state will become -a process commensurate with extinction learning. We further argue this latter component may depend on the quality of integrative support and behavioural change after the psychedelic experience e.g., removing or revising situational reinforcers -including interpersonal relationships that explicitly or inadvertently work to support the maladaptive habits. The ideal consequence of psychological destabilisation and good subsequent integration is that a broader, more flexible global state space is promoted and sustained. The process of destabilisation may cause the enhancement of features of criticality, as the global system moves out of a subcritical regime associated with ill health. Such features might include critical fluctuations, cascading, long-range correlations, scale-free or fractal dynamics and critical slowing down (e.g.,. It is telling that many of these signatures of criticality have been observed in the brain under psychedelics. Here we argue that the phenomenon of destabilisation applies at social, psychological and biological scales -as is characteristic of CST mechanics. The next section expands on the notion of destabilisation, and explains how psychedelics act as destabilisers to promote mental health.
DESTABILISATION AND PSYCHEDELIC THERAPY
The next generation of medical interventions will arguably target stability and change. Broadly defined, destabilisation has been a prominent concept in psychotherapy, often identified as a key mediator of psychological and clinical change. Correspondingly, in CST, destabilisation can be studied as a loss of pull from particular attractors e.g., principally, by injecting noise, energy, excitation or temperature into the system. In a free-energy scheme, the lowering of basins of attraction is commensurate with reducing their precision-weighting -and thus, in a Bayesian formulation, the precision weighting of priors. When this process occurs in a system that could be tuned closer to criticality (as opposed to over a tipping point into white noise -or pure randomness), such changes can give rise to interesting dynamical phenomena such as critical fluctuations and critical slowing down) -which can be measured and quantified. Evidence shows that psychological destabilisation, measured as increased fluctuations in psychological states, is a predictor of clinical change in both coded observational data of therapy sessions and repeated self-ratings. Such psychological destabilisation can be interpreted as early indicators for upcoming clinical transitions. Destabilisation could also be measured neurobiologically e.g., via measures of brain entropy, diversity or complexity. When destabilised, a system can gain more diversity in its dynamics or range of possible behaviours -i.e. it gains more degrees of freedom. This may have a number of interesting consequences if, for example, it tunes the system closer to criticality. For example, systems tuned closer to criticality often exhibit a longer recovery time after a given perturbation -a phenomenon known as 'critical slowing'. One can draw parallels between critical slowing in CST and sensitivity to perturbation. In psychedelic therapy, greater sensitivity to perturbation could be related to the strongly hypothesised exaggerated influence of context on outcomes, some concrete examples of which include sensitivity to the therapeutic allianceand the music played during the dosing session. If the contextual conditions are adverse, however, one can imagine how small perturbations could cause spiralling ruminative 'loops' that are difficult to break out of. Another way we can view critical slowing is in relation to the ability to 'bounce back' from adverse conditions, where increased critical slowing would parallel a reduced ability to bounce back, or rather a greater sensitivity to perturbation. On a trait level, one might hypothesise that highly sensitive or susceptible individuals -or so-called 'orchids' -should be more susceptible to mental illness, a relationship for which there is much evidence. This relationship may also bear relevance to the sometimes described 'thin skinned' or 'open hearted' quality of individuals' in the aftermath of a psychedelic experience, where interpersonal support and a grounded psychosocial matrixmay be vital for a positive therapeutic trajectory (seefor relevant material). Conversely, if the psychosocial matrix is adverse for such thin-skinned individuals, analogous to 'returning to earth with a bump' -there could be a heightened risk of iatrogenesis. These insights could inform therapeutic approaches in psychedelic therapy, where e.g., once the psychopathological attractor is destabilised, subsequent treatments targeted at supporting an alternative, healthier state space are promoted -a process also known as integration. This process may work best if participants are not too heavily primed with new belief systems and behavioural schemas. One can easily imagine how priming could go awry or raise ethical objections if not professionally managed. For example, objections could be raised regarding the manipulation of impressionable individuals via the pro-plasticity effects of psychedelics. This matter touches on old controversies in psychotherapy that could easily re-emerge in the context of psychedelic therapy if not preempted and safe-guarded against. For example, the problem of 'false memories', the implanting or priming of false or questionable inferences and relational or sexual 'boundary crossing' are relevant here) -and have already been reported in the context of psychedelic therapy. One way to tackle these risks is to address them in therapist training and to monitor preparation, dosing and integration sessions to ensure good practice. Briefly, the ideal is to promote an open enquiring mindset, not one that is indoctrinated or manipulated in a specific way. Destabilisation can promote the breaking up of persistent, overly reinforced patterns of thinking and behaving, and a light, undirected but empathetic approach from therapists is arguably the best way to avoid new reinforcements or even, in the worst of cases, re-traumatisation via the unprofessional repetition of boundary incursions. As seen in Section 2, the goal of psychotherapy is to weaken unhealthy patterns of thinking by bringing memories, feelings, thoughts, actions and relationships into perspective, i.e. by nesting them in an extended context of mutual dependencies and relations that can then be slowly processed and understood. More traditional psychotherapeutic techniques and methods, as well as spiritual practice, can help to achieve these aims, but the processes that lead up to such epistemic development can be greatly catalysed by the basic destabilising action of psychedelics. The challenge for psychedelic therapy is to do this in a way that is sustainable and does not, for example, involve the bypassing of a full maturational development. The basic entropic action of psychedelics is linked to a rich psychological experience that enables novel or diverse cognitive and affective perspectives. This richness and novelty is arguably the inverse of the narrow cognitive and behavioural styles that characterise psychopathology. Subjective rating scales exist for measuring aspects of the psychedelic experience, such as the Emotional Breakthrough Inventory (EBI, see alsoand the Altered States of Consciousness scale. There are also useful scales that are arguably best applied in the days after a psychedelic experience (the so-called 'after glow' period), such as the Psychological Insight Scale. Some researchers have also made use of simple single item ratings, measuring such phenomena as the 'richness of experience', 'ego-dissolution', and the intensity of complex and simple visual imagery. Viewing these scales and the experiences they pertain to can enable us to understand dynamical processes of destabilisation and the 'positive' and 'negative' psychological phenomena that parallel them, by which we mean phenomena that are gained or enhanced (i.e., positive) or lost or diminished (i.e., negative). Examples of positive or 'gain' phenomena include 'insight', 'visions', 'challenging states', 'mystical type experiences' and 'emotional breakthroughs' -and examples of negative or 'loss' phenomena include 'ego-dissolution'. The notion of 'emotional breakthough' is becoming particularly relevant in as a strong predictor of positive therapeutic outcomesIt is important to emphasise that specific experiences should not be viewed as reliable effects of a direct drug action but rather experiences whose likelihood of occurring is increased by a direct drug action but that critically depend on contextual influences. The popularised term 'set and setting' is often used in relation to psychedelic experiences, with 'set' referring to the preparation of the individual (including his/her personality structure, expectations and mood at the time), while 'setting' accounts for (physical, psychological and socio-cultural) characteristics of the environment in which the experience takes place. Overall, in this section, we have cast the destabilising action of psychedelic drugs in a context of psychedelic therapy. Leveraging principles from complexity science, we explored the idea that psychotherapy may trigger clinical change by destabilising unhealthy patterns of thinking, and that psychedelics are strong candidates for catalysing this. The widening of a self-centred point of view is ideally paralleled by a generalised sense of connectedness, tenderness and peace that enables an unhurried re-processing of one's past, present and future that is practised as well as realised.
DISCUSSION AND SYNTHESIS
We believe that the cognitive neuroscience of conscious experience and the basic and therapeutic action of psychedelic compounds, can benefit from incorporating insights and methods of dynamical complex systems theory, adaptive networks, and the Free Energy Principle framework. It is our view that CST offers an approach that is respectful to phenomenology of lived experience and does not suffer from the pitfalls of an eliminativist or excessively brain centric approach to consciousness and the psychedelic experience. This is arguably because CST acknowledges -if not promotes -an appreciation of emergent and dynamical phenomena that resonate well with psychological phenomena of great relevance to the psychedelic experience, mental health and psychedelic therapy. By applying CST to psychedelic therapy for common mental health issues, we find that it is possible to explain their action under a common framework. The relaxed beliefs under psychedelics (REBUS) model, a popular interpretation of psychedelic action, posits that psychedelics work to relax high-level priors and hence open the subject up to new perspectives and interpretations of itself and its environment. The REBUS model provides an integration of the entropic brain hypothesis and the free-energy principle framework in proposing that the entropy-enhancing action of psychedelics works to flatten the mind and brain's dynamical landscape, allowing the global system to escape from excessively reinforced local optima (e.g., associated with symptoms of mental illness) and thus, in time, explore a broader, more balanced global state space e.g., where healthier ways of thinking and behaving can be cultivated. The entropy-enhancing and belief relaxing capability of psychedelics directly relates to their destabilising capability while the heavy reinforcement of attracting local optima corresponds to heavy weighting of priors and excessive rigid styles of thinking and behaving that become the target for psychedelic therapy. Hence, by bringing a complex systems perspective to psychedelics, we hope to provide a roadmap towards a fuller account of how the mind and brain can be reconfigured by the destabilisation action of psychedelics -and potentially other interventions that share this core property. Viewing REBUS in relation to complex systems theory offers a way to understand the interrelationship between such psychological constructs as destabilisation, uncertainty, conscious experience, beliefs, assumptions, habits, belief relaxation, precision weighting, confidence, learning, reinforcement, de-weighting, emotional breakthrough, insight, integration and more -and nicely prepares us for addressing their neurobiological correlates via methods such as brain imaging. One interesting offshoot of our application of CST to psychedelics is what it suggests about the nature of psychological health. That is, according to our model, health may be defined by the breadth and depth of 'nesting' or harmonics between different components of mind, brain and behaviour. Thus, healthier global patterns or dynamics should feature the nesting of psychological states (and the brain states they relate to) into an extended set of patterns or state dynamics. This general rule of neater nesting or harmonics relating to healthier states of mind, should apply within the brain, between the brain and body and between the body and other living beings and systems. For example, the rhythms and dynamics of these various systems and their sub-systems should ideally inter-relate in a mathematically logical way, as is the case e.g., with harmonics in sound and music. At this stage, this model is admittedly loose in detail, but we believe it holds much intuitive appeal and could help to explain the so-called unitive or non-dual experience associated with psychedelics and certain meditative states as well as the sense of interconnectedness that can follow from psychedelic experiences. The so-called 'symmetry theory of valence' is relevant here; see also. In our view, this model is deserving of focused empirical investigation, particularly given the relatively poor grasp contemporary cognitive neuroscience has over the biology of valence specific emotion, and what an improved understanding could achieve for mental health research and care.
CONCLUSION
There is growing evidence for the therapeutic value of psychedelic therapy but there is a great need for a better understanding of how it can achieve positive therapeutic results. Here, we review the REBUS model, according to which psychedelics increase both the entropy of spontaneous cortical activity and in parallel, the richness -or depth of content -of psychological experience, but couch it in relation to complex systems theory (CST). This novel approach leads us to posit that psychedelics act as destabilisers, both in a psychological and neurophysiological sense, dismantling overly reinforced set-points or attractors that relate to overly reinforced or weighted priors, beliefs or assumptions -such as those that underlie symptoms of mental illness. Our CST based approach explains that an initial entropic and destabilising drug effect causes an effective relaxation of local optima -presenting a special opportunity for a topological reconfiguration of the global energy landscape of the mind and brain, an effect that will best harnessed by twinning psychedelics with appropriate psychological support -including post-dosing psychological integration. We end with
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