Your Brain Is Not an Onion with a Tiny Reptile Inside

March 2024 update:

I recently read this research article on neuroanatomy. I think it quite clearly communicates the real way our nervous system contributes to and influences our behavior. Although the Triune Model can be a helpful and useful model for thinking about the brain and its affect on behavior, it is in many ways wrong.

The article discusses just how wrong the model is and how it has affected our understanding of the brain. The authors also contribute a new point of view from which to think about the brain and behavior. I think it might be confusing to some people who are relatively new to studying the brain, so I’m going to record a video lecture reviewing this paper in more detail.

For now, I had GPT-32K generate a summary of the article while I prepare and edit the video lecture. One potential confusion the article may lead to is how one can reconcile the new point of view the authors suggest with other models like the System 1 and System 2 Model from Dr. Daniel Kahneman (which I discuss in Models of Neuromarketing Parts 1A, 1B, and 1C) . Accordingly, I had GPT-32K write a quick way you can think about reconciling System 1 and System 2 with a realistic view of neuroanatomy. Again, I’ll be recording a video lecture on this topic soon. It takes me a good bit of time to prepare the lectures, record them, and edit them, so I hope you find these helpful in the meantime. Just reach out to me if you have any questions 🙂

Summary of the Research Paper

The article “Your Brain Is Not an Onion With a Tiny Reptile Inside” by Joseph Cesario, David J. Johnson, and Heather L. Eisthen critiques a common misconception in psychology about the evolution of the vertebrate brain. This misconception is that newer, more complex brain structures were added over older, simpler ones as vertebrate species evolved. This view, often described as the “triune-brain theory,” suggests that humans have unique brain structures for complex functions like language and reasoning, layered over more primitive parts responsible for basic survival functions and emotional responses.

The authors argue that this view, although prevalent in psychology textbooks, is not supported by neurobiology or evolutionary science. They emphasize that brain evolution does not work in a linear fashion with newer structures simply added to older ones. Instead, all vertebrates share basic brain regions, which have evolved in form but not fundamentally changed or been added to over time. For example, the cortex is present in all vertebrates and has not been uniquely added in humans or mammals.

The article also discusses how this misconception has influenced psychological research and theories, particularly those that draw distinctions between ‘primitive’ and ‘advanced’ brain functions or between ’emotional’ and ‘rational’ processes. The authors suggest that this flawed understanding may lead researchers to overlook similarities between human and non-human animal behavior and cognition, and could limit the integration of psychological research with evolutionary and developmental approaches.

The authors call for psychologists to update their understanding of brain evolution and consider the implications of a more accurate model for psychological theory and research. They suggest that by recognizing the commonalities across species and the evolutionary transformation of existing brain structures, rather than the addition of new ones, researchers can gain a deeper and more accurate understanding of brain functions and behavior.

Reconciling with the System 1 and System 2 Model of Behavior

Note from Devan: The short version – don’t think of system 1 and the behaviors it may lead to as simply being your “old, ancient, primal” brain. Your brain’s pre-frontal cortex (PFC) and other anatomy (brain parts) that are more connected to higher thinking, decision making, and long term planning do still play a role and influence decision making. It’s not like your PFC is just “off” at times. You may not always be making extremely rational decisions, but that does not mean your PFC and the other frontal areas of your brain weren’t involved.

GPT Answer here:

Reconciling the accurate model of brain evolution with the System 1 and System 2 framework requires a shift in how we conceptualize these systems. The System 1 and System 2 model, popularized by Daniel Kahneman, describes two types of cognitive processing: System 1 is fast, automatic, and often unconscious, while System 2 is slower, more deliberative, and conscious.

The traditional view, influenced by the outdated triune brain theory, might suggest that System 1 processes are tied to the ‘older’ parts of the brain (like the limbic system), responsible for instinctual and emotional responses, and that System 2 processes are linked to the ‘newer’, more evolved parts of the brain (like the prefrontal cortex), which handle rational thinking and decision-making. This view, however, is not supported by current neurobiological and evolutionary understanding.

Here’s how we can reconcile these systems with a more accurate view of brain evolution:

1. Functional Overlap and Integration: Modern neuroscience shows that brain functions are not isolated to specific, newer or older regions. Cognitive processes, whether fast or slow, often involve widespread networks across the brain that include both evolutionarily ancient and more recently developed structures. This means that both System 1 and System 2 processes are likely to involve integrated action of various brain regions, not just a simple division between ‘old’ and ‘new’ brain areas.
2. Evolutionary Perspective on Cognitive Processes: From an evolutionary standpoint, both types of cognitive processes have evolved to meet different adaptive challenges. System 1 processes allow for quick, efficient responses to environmental stimuli, which can be crucial for survival. System 2 processes, while slower, enable more complex planning and problem-solving that can also be beneficial for survival in different contexts. Both systems are not markers of a linear progression from primitive to advanced but are different strategies that evolved to handle different aspects of an organism’s interaction with its environment.
3. Behavioral and Cognitive Flexibility: The idea that some vertebrates are ‘stuck’ with only reflexive, stimulus-driven behavior (System 1) while others, like humans, have the added benefit of higher-order reasoning (System 2) is misleading. Research shows that many non-human animals exhibit flexible, complex behaviors that suggest both types of cognitive processing. This indicates that the distinction between System 1 and System 2 should be seen more as a functional difference in cognitive strategies rather than a fundamental structural evolution of the brain.

In summary, reconciling the System 1 and System 2 framework with an accurate model of brain evolution involves recognizing the integrative and overlapping nature of brain functions and viewing both systems as evolutionarily adaptive cognitive strategies that are not tied to a simple old/new brain dichotomy. This perspective encourages a more nuanced understanding of how different cognitive processes might work together, involving various brain regions, to support adaptive behavior in humans and other animals.