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’.


“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.”

Authors: ‪Inês Hipólito, ‬Jonas Mago, Fernando E. Rosas & Robin L. Carhart-Harris



We propose that psychedelics act as destabilisers in a psychological and a neurophysiological sense, and that this action is paralleled by a relaxation of prior assumptions. This approach helps explain how psychedelics induce increases in brain entropy and the subsequent sub-acute period of potential recovery.


Psychedelics are becoming increasingly accepted and de-stigmatised, and are being investigated for their potential as a treatment for psychopathology. They have low addictive properties and other physical side-effects, which gives them an advantage over several currently approved drug treatments.

Recent evidence suggests that psychedelic therapy may have significant and sustained antidepressant and anxiolytic effects, even for individuals with treatment-resistant depression, as well as in cases of PTSD, eating conditions, OCD and other common mental health conditions.

Psychedelics trigger experiences that many subjects regard as insightful and replete with meaning. This epistemic quality to psychedelic medicine may explain why it can endure – as well as what fails when it does not.

While we recognise the importance of understanding psychedelics through a psychological lense, we also value the importance of a biological comprehension of their action. This could help mitigate risks of mis-application, and validate their medicinal action and value.

The present paper takes inspiration from Complex Systems Theory (CST) and argues that psychedelics act as destabilisers on set-points that become stereotyped in psychopathology, through repetition and reinforcement.

The treatment effect of psychedelics is often described in reference to the destabilisation or disruption of globally distributed brain dynamics. This idea is inspired by empirical findings showing that the psychedelic experience coincides with an increase of entropy in properties of spontaneous brain activity. A decrease in the precision of spontaneous brain activity can be related to an increase in the entropy.

The relaxed beliefs under psychedelics (REBUS) model is a unifying theory of the brain and psychological action of psychedelic compounds. The brain and behaviour organise themselves to minimise surprising encounters with the world by maximising the reach, reliability and efficiency of their internal models. The REBUS model proposes that the entropy-enhancing action of psychedelics works against the imperative of maintaining a stable top-down percept, by creating a basal sense of felt uncertainty as the content of consciousness becomes unpredictable and ‘enriched’ relative to normal waking consciousness. One might hypothesize that psychedelics may impact learning traps and associated cognitive misadjustments, potentially yielding performance benefits. However, any hypothesised performance enhancement is likely to be dose-dependent, and may ‘topping-out’ into non-specific deficits above a certain dose range. The REBUS model integrates the entropic brain hypothesis and the free energy principle framework. It uses entropy as a measure of uncertainty.

The REBUS model has been supported by a number of empirical findings, including increased brain entropy in relation to the psychedelic state, decreased brain entropy under states of reduced consciousness, and flattening of the brain’s energy landscape under psychedelics.

An increase in the entropy of spontaneous cortical activity during the psychedelic state can be explained using dynamical/complex systems theory.

  1. Philosophical Psychology: Psychological Phenomena?

There is growing evidence that psychedelics can have a positive impact on mental health, and that the subjective effects of psychedelics are predictive of their enduring therapeutic effects. We also hypothesise that the entropy of spontaneous cortical activity will emerge as valuable explanatory and predictive markers of action.

In the present work, we give an appropriate level of attention to psychosocial factors relevant to the psychedelic experience. We adopt a relational and context sensitive and dependent approach, which is consistent with the philosophical psychology of Ludwig Wittgenstein.

Many psychotherapies aim to help the patient better understand difficult memories and emotions, and to replace ‘unhealthy’ patterns of thinking and behaving with ‘healthier’ ones, by helping the patient discover their own desire for better alignment with societal norms and values.

  1. Complexity Science: Essential Terminology

Complex systems are those whose behaviour results from a highly non-trivial aggregation of interactions, including multi-scales, complex external influences, nonlinearity, feedback loops, and multiplicity.

Complex systems theory is an interdisciplinary research programme that aims to understand the underlying common features of complex systems that arise in different levels of nature.

Complex physical systems and biological processes can self-organise without external direction or control, and attain states of “spontaneous” order which seem to defy the second-law of thermodynamics.

Self-organised critical systems are subject to regular, complex interactions between and within their parts, and between the system and complex external influences. They tend towards distinctive types of intrinsic dynamical organisation, and can be viewed as surfing uncertainty or entropy. Complex systems can be studied as dynamical, and their trajectories can be mapped as a trajectory in time. This trajectory shows the behaviour of the system, which tends to fixed stable or semi-stable points, known as attractors, and avoiding fixed unstable points, known as repellers. A way to conceptualise complexity is by how difficult it is to model a resulting behaviour. This is important when planning interventions, such as mental health interventions. Sudden transitions can have a huge impact on a complex system, such as global changes in climate, shifts in ecosystems, crashes in financial markets, and iatrogenic transitions in psychological status.

Non-resilient complex systems can tip, causing turbulence in the whole system. Tipping can be induced 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.

  1. Psychopathology from a Complexity Science perspective

Here we apply a complexity theory approach to our understanding of psychopathology, and we focus on three main components: the emergence from a wholeness, a specific pattern or order, and the notion of “stuck” states. Psychotherapeutic intervention can be thought of as aiding recovery via intentionally causing an initial and vital destabilisation.

Psychopathology is a complex system that has to be understood as a whole. This means taking into account the psychological experience situated in a sociocultural setting. Seeing psychopathology from the lens of complexity science lends support to the controversial position that symptoms of mental illness should not necessarily be seen reflective of a discrete disorder per se, but rather of a different kind of order, a re-ordering, that arises when specific patterns form within a complex dynamical process. A dynamical view of psychopathology can be developed following an enactive approach, which is operationalised via tools from dynamical systems theory. This view shows that individuals are evolving coupled with their sociocultural environment, and that they can have multiple attractors and dynamically switch between them. The ways in which an individual navigates its attractors determines its behaviour, which feeds back into its environment and determines the future dynamical geometry it will observe.

Emotional states can be seen as attractors, and the more an individual visits an attractor point, the more likely they are to visit that same point again. This process is consistent with experience dependent plasticity and reinforcement learning, and is the process by which attractors deepen.

Biological systems are always subject to noise, but attractor states represent favoured states that the system tends to stabilise into. This property can become problematic when the attractor becomes too reinforced or rigid. The paradox of stable attractor states is that they can provide a rewarding and attractive low level of uncertainty, but also reduced degrees of freedom, and therefore a ‘narrower’ state of being. This stereotypy is the first component of mental illness. A common example of a stuck state is rumination, which can easily turn into a psychopathological condition. Patients with depression often continually ruminate about their failings, reiterate thoughts of guilt, and engage in self-critical inner narratives. Addiction and obsessive-compulsive disorder drive behaviour that is specific, narrow, and rigid; rumination about threats to the person can reinforce the disorder.

Psychopathology is better understood not by the nature of the beliefs supporting given thoughts or behaviours, but by the weight they are given, and the relative difficulty if not apparent ‘impossibility’ of moving away from the state. The illness rests with the inter-relationships and dynamics of specific states, not with the content of these states. Healthy systems and individuals are able to bounce back from stressful events. Agents deal with uncertainty by adapting to surprising events, including by updating their assumptions or altering their behaviour. However, agents do not simply find a dark corner and stay there. When faced with a surprising event, an agent can either tend towards a stuck state or reduce its surprise by adapting to the environment. A stuck state can be seen as potentially entering a phase transition towards a psychopathological situation. Lastly, a high tolerance of uncertainty may be conducive to resilience and thus, good psychological health. This style of free-energy minimization and ‘light belief’ is associated with Buddhist philosophy and practice as well as third wave psychotherapies. Meditation practices can help cultivate compassion, acceptance and self-awareness, which are useful in the psychological integration process, which is considered by many to be a critical component of safe and effective psychedelic therapy. We argue that in order to get out of a stuck state, one has to increase the entropy of the system or decrease the temperature of the system. This is done by either removing or revising situational reinforcers or by increasing the time spent away from the old attracting state.

The process of destabilisation may cause the enhancement of features of criticality, such as critical fluctuations, cascading, long-range correlations, scale-free or fractal dynamics and critical slowing down. These features have been observed in the brain under psychedelics.

  1. Destabilisation and Psychedelic Therapy

The next generation of medical interventions will arguably target stability and change, and destabilisation is a prominent concept in psychotherapy. Destabilisation can be measured and quantified, and is a predictor of clinical change in both coded observational data of therapy sessions and repeated self-ratings.

Destabilisation could be measured neurobiologically via measures of brain entropy, diversity or complexity. This could have a number of interesting consequences, such as tuning a system closer to criticality or causing it to exhibit a longer recovery time after a given perturbation.

Critical slowing can be related to the ability to bounce back from adverse conditions, and this relationship may be relevant to the ‘thin skinned’ or ‘open hearted’ quality of individuals in the aftermath of a psychedelic experience. These insights could inform therapeutic approaches in psychedelic therapy, where participants are not too heavily primed with new belief systems and behavioural schemas. This could raise ethical objections if not professionally managed, and could lead to false memories, false inferences and relational or sexual boundary crossing.

Psychotherapy aims to weaken unhealthy patterns of thinking by bringing memories, feelings, thoughts, actions and relationships into perspective. Psychedelics can help with this process, but the challenge is to do this in a way that is sustainable.

Psychedelics induce a rich psychological experience that enables novel or diverse cognitive and affective perspectives. Several scales exist for measuring aspects of the psychedelic experience, such as the ‘richness of experience’, ‘ego-dissolution’, and the intensity of complex and simple visual imagery. We can use these scales to understand dynamical processes of destabilisation and the ‘positive’ and ‘negative’ psychological phenomena that parallel them, such as insight, visions, challenging states, mystical type experiences and emotional breakthroughs.

A psychedelic experience depends on the individual’s preparation, expectations and mood at the time, as well as the physical, psychological and socio-cultural characteristics of the environment in which the experience takes place.

In this section, we have explored how psychedelic drugs can help to destabilise unhealthy patterns of thinking and how this can be used to trigger clinical change.

  1. Discussion and synthesis

We believe that incorporating insights and methods of dynamical complex systems theory, adaptive networks, and the Free Energy Principle framework into the cognitive neuroscience of conscious experience and psychedelic compounds can be beneficial.

By applying CST to psychedelic therapy, we can explain their action under a common framework. This framework integrates the entropic brain hypothesis and the free-energy principle framework, and proposes that the destabilisation action of psychedelics opens the subject up to new perspectives and interpretations of itself and its environment.

Viewing REBUS in relation to complex systems theory offers a way to understand the interrelationships between psychological constructs and their neurobiological correlates. According to our model, psychological health is defined by the breadth and depth of ‘nesting’ between different components of mind, brain and behaviour. This rule applies to the brain, body and other living beings and systems. This model of valence specific emotion holds much intuitive appeal, and could help explain the unitive or non-dual experience associated with psychedelics and certain meditative states.


We review the REBUS model of psychedelic therapy, which posits that psychedelics increase both the entropy of spontaneous cortical activity and in parallel, the richness of psychological experience. We then discuss how this effect can be harnessed by twinning psychedelics with appropriate psychological support.


Authors associated with this publication with profiles on Blossom

Fernando Rosas
Dr. Fernando E. Rosas is a Postdoctoral Researcher at Imperial College London, based at the Centre For Psychedelic Research.

Robin Carhart-Harris
Dr. Robin Carhart-Harris is the Founding Director of the Neuroscape Psychedelics Division at UCSF. Previously he led the Psychedelic group at Imperial College London.

Linked Research Papers

Notable research papers that build on or are influenced by this paper

REBUS and the Anarchic Brain: Toward a Unified Model of the Brain Action of Psychedelics
The REBUS and the anarchic brain hypothesis paper (2019) argues that psychedelics relax the precision of high-level priors or beliefs, thereby liberating bottom-up information flow, particularly via intrinsic sources such as the limbic system.

PDF of Pattern Breaking: A Complex Systems Approach to Psychedelic Medicine