Science Converging on Psychotherapy: Part 3

Physics and mathematics help us understand psychotherapy.

Posted Jul 09, 2020

Dan Dennis/Unsplash
Source: Dan Dennis/Unsplash

This third and last post of the series looks at a relatively new addition to the theoretical foundation taking shape beneath the traditions and wisdom of over a century of thought about psychotherapy.

Karl Friston, a British psychiatrist and neuroscientist, has developed a way to link study of the mind with the broader sciences of physics and information theory. In doing so, he addresses a serious problem with psychotherapy theory.

As pointed out in previous posts, most existing theories are self-referential, that is, based on the very concepts they aim to explain. The best theories tie to “general principles independent of the thing to be explained.”

In this post, the aim is to make Friston’s work accessible, hopefully without losing too much of its subtlety. He bases his work on two ideas, the Free Energy Principle and the Bayesian Brain Hypothesis.

The Free Energy Principle

Heretofore, science has not provided an overall explanation of individual human irrationality. Specific maladaptive patterns have been explained, but there has not been a general formulation of why irrationality and maladaptive responses are endemic to humankind. What Friston does is to provide a unitary formulation of the aim of life itself, including the body at every level as well as the human mind. They are designed and function to “minimize free energy.”

As it turns out, this is close to a restatement of the theory of evolution. Evolution serves the “purpose” of natural selection (of the fittest). The Free Energy Principle says that non-equilibrium, self-organizing systems (such as life) maintain themselves and avoid extinction by minimizing free energy.

Free energy is a slightly confusing term, originally from physics, meaning “energy available to do work.” We might think of free energy as the kind of energy that is wasted in oil drilling when unused gas is “flared” into the atmosphere. Free energy is lost energy that moves the universe one step closer to entropy, where all matter is evenly distributed at a uniform temperature, in perfect equilibrium and everything is dead.

Life is the opposite, where all organisms use energy from outside (e.g. light, nutrients) to maintain boundaries, inner organization, the ability to multiply, and the ability to resist the constant tendency towards dissipation of free energy, disorganization, individual death, and species extinction. Thus, Friston’s idea that living things minimize free energy runs parallel to Darwin’s theory of evolution in stating that living things are naturally selected to avoid death and extinction by holding tightly to the boundaries, organization, and ability to adapt to changing environments that are essential to all life.

For humans, in general, minimizing free energy means constantly adapting to a changing and challenging environment. When we lose that ability, we face individual death and species extinction.

According to Friston, the brain can be understood as an organ evolved to promote adaptation by making inferences (predictions) about our environment so as to allow us to respond (minimize free energy) as effectively as possible. For example, if we can’t predict where we will find food, then soon we become too weak to keep warm or ward off predators, and we die. If we fail in predicting what will bring social acceptance, we lose the support of the community and eventually fail to reproduce or die.

In applying the Free Energy Principle to the human mind, Friston makes use of a relatively recent view of free energy from the domain of information theory. Here, free energy is defined mathematically in a way closely analogous to its definition in physics. Qualitatively, this form of free energy is that which contributes to chaos, uncertainty, or “surprise.”

One might picture a professional gambler wishing to minimize free energy, that is, unpredictability. By counting cards and memorizing precise odds ratios, the gambler attempts to maximize statistical predictability and minimize surprise, otherwise known as free energy. As long as statistics hold, he or she will ultimately win. According to Friston, this is also the universal aim of the human mind, including both rational and irrational patterns of response.

Thomas Bayes, an eighteenth-century protestant minister, worked out the math of prediction. His equation made it possible to determine probability in the form, “if this circumstance exists, then what is the likelihood of that happening?” 

The “Bayesian Brain” uses its own (quite effective) methods to approximate Bayes’ equation by constantly comparing successive predictions with sensory inputs and minimizing the difference between the two. The degree of mismatch is technically known as “Prediction Error” (PE). Minimizing PE, or surprise, is how the brain minimizes free energy and arrives at the best adaptation.

The Bayesian Brain is limited to three ways to reduce Prediction Error:

  1. Act to change the environment so that sensory inputs better match expectations (e.g. aggression to obtain what is desired).
  2. Alter interpretation of incoming data (e.g. defenses such as denial). 
  3. Change the internal model of the world (what therapy usually seeks).

At last, then, we arrive at a universal and scientific explanation of those irrational interpretations, actions, and beliefs that are the targets of all schools of psychotherapy. They represent the mind’s erroneous attempts to minimize free energy. For example, a child who has learned that helplessness is rewarded with attention, may, as an adult, continue to function according to that model, despite the fact that the behavior is highly maladaptive.

Actions (such as helpless behavior in the example above) may fail to produce the desired result. Incorrect interpretation of sensory data (e.g., an ex-soldier misinterprets automobile backfire as gunfire) can have negative consequences. And frequently, faulty internal models lead to unrealistic expectations, irrational actions, and erroneous appraisals as the mind operates automatically to do what it has evolved to do: minimize free energy by making its best predictions in an ever more complex and fast-changing world.


While not without some controversy, Friston’s approach to a theory of mind is of remarkable value to the field of psychotherapy. It puts appropriate emphasis on the extensive non-conscious information processing that produces not only maladaptive involuntary actions, but also conscious impulses, thoughts, and feelings that lead to irrational choices. Furthermore, it gives us a universal explanation of the purposefulness and energy with which the human mind pursues even irrational goals, and finally, it gives us a therapeutic tool, namely, identifying faulty internal models, that may be the targets of our interventions.

And, most relevant to the aim of SEPI, Friston’s work applies to all contemporary orientations, schools, lists of common factors, and metatheories of psychotherapy.

[For a view of how this applies to practice, see the SEPI Convergence SIG’s 2020 Poster, The Common Infrastructure of Psychotherapy]

—Jeffery Smith, M.D.


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