Neuromyths, part 2: We have a 'reptilian brain'

After demystifying the concept that we only use 10% of our brains, let's tackle one of the most prevalent neuromyths in the history of neuromyths :) The idea that we have a 'reptilian brain'.

The underlying message: We are at the mercy of a 'lizard' inside.

The concept behind the ‘triune brain’ or ‘reptilian/lizard brain’ was proposed by neuroscientist Paul MacLean in the 1940s. MacLean later suggested that the human brain is divided into three layers that each emerged in stages in the course of evolution, with the oldest ‘reptilian complex’ controlling basic functions like movement and breathing; next the limbic system, controlling emotional responses; and finally, the cerebral cortex controlling language and reasoning.

MacLean’s ideas were already known to be incorrect by the time he published his 1990 book. However, even despite the mismatch with current understandings of vertebrate neurobiology, MacLean’s ideas remain popular; mostly because of their simplicity.

The idea of the ‘triune brain’ can be captivating as it also can be seen as a biological 'proof' to Freud's psychoanalytic theory of personality: the id, ego and superego mapping into the reptilian, limbic and cortical brains. Or perhaps even being linked to the concept of the tripartite Platonic soul.

The idea is widely used to describe our reaction to threats, explain human behaviour, or rather the irrationality of human behaviour, by which emotions dominate rational thought or logic.

But: Just because a model is simple, convenient and easy doesn’t make it accurate.

The problem with the ‘triune brain’ concept is that this model is out-of-date and not based on contemporary science, and has been widely discredited by neuroscientists and evolutionary biologists.

• The first problem is that these ideas reflect a ‘natural ladder’ view of evolution, in which animals can be arranged linearly from the more ‘simple’ to the most ‘complex’ organisms. This view is unrealistic since neural and anatomical complexity evolved repeatedly within many independent lineages.
• This view also implies that evolutionary history is a linear progression in which one organism evolved into another and then another. Instead, the correct view of evolution is that animals radiated from common ancestors. Within these radiations, complex nervous systems and sophisticated cognitive abilities evolved independently many times.
• Another - and perhaps most important - problem with this view is the implication that anatomical evolution proceeds in the same fashion as geological strata, with new layers added over existing ones. Instead, much evolutionary change consists of the transformation of existing parts.

The notion of layers added to existing structures across evolutionary time as species became more ‘complex’ is therefore simply incorrect.1

In short: Your brain is not an onion with a tiny reptile inside.

What is even more important, the reptilian brain analogy falls apart when we consider our up-to-date understanding of the neurobiology of emotions and behaviour.

The classic model of emotion goes something like this: You're born with an innate suite of emotions – happiness, sadness, anger, fear. You feel these emotions by perceiving a stimulus that triggers a circuit in your brain. That then causes a bodily response, which causes you to behave a certain way. The classical view assumes that emotions happen to you.

A new theory of ‘constructed emotion’, proposed by neuroscientist Lisa Feldman Barrett overturns this old model.2 According to Barrett, emotions aren’t reactions to the world. Rather, emotions actually construct our world. This theory proposes that a set of emotions are not pre-programmed into our brains. Instead, various ‘ingredients’ are processed by entire brain networks to ‘construct’ consciously experienced feelings in the moment. We may have more control over our emotions than we think.

Joseph LeDoux has reached similar views and proposed a similar theory of emotion construction. He profoundly noticed, “There is no fear center out of which effuses the feeling of being afraid. "Fear" is, in my view, better thought of as a cognitively assembled conscious experience that is related to threat processing, but that should not be confused with the non-conscious processes that detect and control responses to threats.”3

As Barrett highlights : “Humans are not at the mercy of mythical emotion circuits buried deep in the animalistic parts of our highly evolved brain: we are architects of our own experience.”4

Magda / www.magdavoigt.com

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References:

1. Your Brain Is Not an Onion with a Tiny Reptile Inside, Joseph Cesario, David J. Johnson, and Heather L. Eisthen, December 2019
2. How Emotions Are Made: The Secret Life of the Brain by Lisa Feldman Barrett & Seven and a Half Lessons About the Brain by Lisa Feldman Barrett
3. The Amygdala Is Not the Brain's Fear Center, Joseph E LeDoux Ph.D., Aug 10, 2015
4. How Emotions Are Made: The Secret Life of the Brain by Lisa Feldman Barrett