What We Talk About When We Talk About Neuroplasticity

Notes on Emergent Paradigms Part IV

“Because we reason in terms of metaphor, the metaphors we use determine a great deal about how we live our lives.”

—George Lakoff

In 2007, Norman Doidge, a Canadian psychiatrist, published a book that would go on to become a New York Times bestseller, The Brain That Changes Itself, about the emerging science and implications of a scientific paradigm that was just beginning to make its way out of the lab and into public awareness—neuroplasticity.

Since then, it has become an almost household term, pointing to the idea that the structure and function of the brain and nervous system are malleable and subject to change throughout one’s life in response to experience and various types of stimuli (pharmacological, electric, etc.).

This was a radical departure from the mainstream view that brain anatomy was fixed, and thus, so were the brain's perceptual, behavioral, and functional capacities.

As Doidge notes in the introduction:

“For four hundred years this venture would have been inconceivable because mainstream medicine and science believed that brain anatomy was fixed. The common wisdom was that after childhood the brain changed only when it began the long process of decline…

A neurological nihilism—a sense that treatment for many brain problems was ineffective or even unwarranted—had taken hold, and it spread through our culture, even stunting our overall view of human nature.”

Culturally, The Brain That Changes Itself is to neuroplasticity what The Body Keeps the Score is to trauma and How to Change Your Mind is to psychedelics—a bestselling, non-fiction rendering of an emergent scientific field for educated but non-technical readers.

And like trauma and psychedelics, neuroplasticity is a term that means a lot of different things to a lot of different people in a lot of different contexts—and comes with a ton of hype.

If you’re a neuroscientist, it is an imprecise umbrella term that could mean many different ways that the structure and function of synapses, dendrites, axons, neurons, circuits, and brain regions change in response to experience, stimulus, and pharmacology, as well as the associated gene expression and phenotypic changes associated with these changes.

This is obviously a technical and complex area that has no end.

On the other hand, as the quote at the top alludes to, we can think about this term metaphorically; after all, the term ‘neuroplasticity’ itself is a metaphor.

In this context, there are a few “flavors of neuroplasticity” that are interesting and helpful in understanding what we talk about when we talk about neuroplasticity and I thought they would make for a good topic in this series on emergent paradigms. They include:

• Hebbian Plasticity

• Critical Period Plasticity

• Canalization

• Neural Annealing

This is not an exhaustive, peer-reviewed account of an insanely complex, technical domain but a metaphorical account of a few “types” of biological change that I hope is useful to help non-technical readers—like me—understand the brain, the mind, and the impact of psychedelics, psychotherapy, and meditation.

Hebbian Plasticity 

Neurons that fire together wire together

Undoubtedly, you’ve heard this phrase before.

It is the mantra most of us have come to associate with the concept of neuroplasticity. However, it points to one of many very specific processes called Hebbian Plasticity.

Coined by psychologist Donald Hebb in 1949, it illustrates the basic mechanism by which synaptic connections between neurons become stronger through repeated activation.

When two neurons are activated simultaneously, the connection between them is enhanced, leading to more efficient communication. It’s a positive feedback mechanism that occurs when a presynaptic cell repeatedly stimulates a postsynaptic cell. With repeated firing, the connection between the two is strengthened.

It also goes in the other direction, whereby the diminished activation between two cells weakens the connection. Thus, Hebbian Plasticity refers to any long-term modification of a synapse, whether it's strengthening or weakening

This process underlies everything from learning new skills to forming new habits, unlearning habits, and even recovering from brain injury. 

Critical Period Plasticity 

When the clay is soft, it is easily shaped

Critical period plasticity (CPP) refers to a specific timeframe in an organism’s life—in humans, this period is the first several years of life—when the brain is exceptionally receptive to certain environmental stimuli, leading to enduring changes in structure and function. 

The CPP is a period when Hebbian Plasticity is upregulated, allowing for increased learning and adaptation that shape sensory functions, language acquisition, and social and emotional learning. 

This is why it is called the ‘formative years’; our experiences in this period literally form who we become.

Importantly, once this period closes, it becomes much harder for the brain to undergo such profound changes in response to external inputs.

Part of the reason why psychedelics are such promising tools for such challenging conditions is because we think that they reopen critical period plasticity.

This comes from the work of UC Berkeley scientist Gul Dolen, who described the molecular biology of this process in the groundbreaking paper published in Nature last year, Psychedelics reopen the social reward learning critical period.

Dolen’s research has explored how psychedelics can induce a state in the brain that mimics the heightened plasticity seen during these critical periods. This effect suggests that psychedelics can temporarily make the adult brain more capable of learning and adaptation.

Canalization

The rigidity of routine: when behaviors become bedrock.

If neuroplasticity describes the brain and nervous system’s capacity for change, canalization is the loss of that capacity.

Canalization refers to the process by which a trait or behavior—for example, negative self-talk and rumination, as in the case of depression—becomes more stable and resistant to change over time.

It is a term that describes entrenched patterns of behavior or cognitive styles that are difficult to modify.

This is a new concept introduced by Robin Carhartt-Harris, Karl Friston, and colleagues last year in their paper Canalization and plasticity in psychopathology.

Despite the complexity and technical aspects of canalization, it is an intuitive idea and even commonly invoked in contexts of trauma and psychopathology.

For example, in therapeutic settings, it is common to look for coping strategies that formed in response to adverse childhood experiences. Years and decades later, these coping mechanisms may still be operational despite the threat no longer being present. 

This is an example of canalization.

Understanding canalization offers insights into why certain cognitive functions are more resistant to change than others and how the brain balances the need for both stability and adaptability.

Important to our understanding of psychedelics, the authors suggest that canalization is a common feature of all mental illnesses and that the molecular mechanism of psychedelics is to, as the previous section suggests, reopen critical period plasticity and create a window for relearning.

Neural Annealing

Melt to mold, cool to hold

Neural Annealing is a concept developed by neuroscientist Michael Johnson and popularized by the Qualia Research Institute.

It is a metaphor that applies a concept from metallurgy—annealing—where controlled heating and cooling are used to alter the properties of a material. 

Johnson describes annealing in the following way:

“Annealing involves heating a metal above its recrystallization temperature, keeping it there for long enough for the microstructure of the metal to reach equilibrium, then slowly cooling it down, letting new patterns crystallize. This releases the internal stresses of the material, and is often used to restore ductility (plasticity and toughness) on metals that have been ‘cold-worked’ and have become very hard and brittle— in a sense, annealing is a ‘reset switch’ which allows metals to go back to a more pristine, natural state after being bent or stressed.”

The Neural Annealing theory suggests a similar dynamic occurs within neural networks of the brain when internal entropy increases.

But what increases entropy in the brain?

One way may be psychedelics.

In the above-mentioned paper, Carhartt-Harris and colleagues refer to this process as ‘Temperature or Entropy Mediated Plasticity’ or TEMP.

They suggest that interventions that trigger an increase in system temperature or entropy—analogous to heating up metal—allow neural circuits to become more malleable and subject to change.

Putting It All Together

I chose these four “flavors” of neuroplasticity because together they offer a conceptual framework for understanding how psychedelics—and other entropy-producing experiences, like mystical experiences, meditation practices, and neurostimulation, for example—lead to the potential for psychological and neurological change.

In other words, psychedelics and entropy-producing experiences, through a process that can be described as neural annealing, reopen a temporary window of critical period plasticity whereby rigid and entrenched—or canalized—beliefs, behaviors, and cognitive styles can become unstuck. With a supportive and coherent integration, new beliefs, behaviors, and cognitive styles can be learned through the process of Hebbian plasticity.