Mythbusters #22 - The triune brain

Does simplifying the brain into three regions help or hinder our understanding of this complex system?

The Claim

The ‘triune brain’ was first proposed by McLean (1969) based on the idea that the brain is divided into three regions : reptilian (instincts), limbic (emotional visceral brain) and the neocortex (abstract thinking, imagination, reasoning etc) which belongs to the primates and humans.

This model of the brain was popularised by Carl Sagan in his book ‘Dragons of Eden’?which describes how human intelligence evolved.

Daniel Goleman in his best seller ‘Emotional Intelligence’ focusses on the amaglada (part of the limbic system) as being the ‘emotional centre’ of the brain. He also states that ‘the brain in prehistory didn’t have a prefrontal cortex’.

In his book Behave (2017), Robert Sapolsky also uses the?'triune brain' to divide the brain into metaphorical

'functional buckets, with the usual disadvantages of categorising a continuum'

Sapolsky also suggests that the prefrontal cortex is the most recently evolved part of the brain and also uses the rational neo cortex v emotional limbic system battleground analogy "pre-frontal cortex activates, blunting activity in the amygdala" (p61)

The triune brain theory is also intuitive and psychotherapists use it because it fits neatly with Freud's idea of id, ego and super ego. Sapolsky also uses the ego id division of the brain as a metaphor (Behave p.57).

The theory also explains other myths such as the ‘amygdala hijack’ i.e., the ‘limbic system’ takes charge in the ‘fight & flight’ response.

The triune brain also gives an intuitive linear understanding of how the brain evolved.?We all evolved from single celled organisms, fish, reptiles etc and new bits of the brain were added on that helped us deal with an increasingly complex world.?Those creatures that missed out on the ‘clever’ bits of the brain (prefrontal cortex) got left behind.

Nearly 90% of introductory psychology textbooks published between 2009 and 2017 explain the evolution of the human brain in this way. But does this fit with the consensus held by contemporary neurobiologists?

Lets investigate...

The Evidence

Brain evolution

The above explanation of how our brains evolved is linear (scalar) from “simple” to the most “complex” organisms.?But (no surprise hopefully) humans (or our brains) didn’t evolve from reptiles.?We evolved completely independently from them developing different more sophisticated cognitive abilities.

This scalar view of evolution has now become extinct among practicing evolutionary neuroscientists (see Hodos & Campbell 1969), but it lives on in many other minds.

But Octopus (an invertebrate hence way down the evolutionary scale) for example have highly complex nervous systems. They have six times more neurons than a mouse (about the same as a dog) & unlike mammals 3/5ths of their neurons are in their ‘arms’ rather than their brain & they are clever. So having a well-developed cortex or a complex brain doesn't necessarily make you 'clever' (behaviourally complex)

Despite considerable interest in the forces shaping the relationship between brain size and cognitive abilities, it remains controversial whether larger-brained animals are, indeed, better problem-solvers

There is also evidence that the “cortex may even pre-date vertebrates” .?All mammals have a prefrontal cortex - the first mammals appeared on earth 210 million years ago which I guess is prehistory? Reptiles, fish & birds also have (always had) a three-layered (triune) brain structure & have complex individual & social behaviours.

So the triune brain doesn't explain the evolution of the brain or how animals create complex behavioural responses.

As Sapolsky suggests "evolution is a tinkerer not an inventor" - (p381 Behave). Just like feathers were not invented for flight but for insulation the cortex was not invented to make more 'intelligent' beings, evolution just modified its function e.g. in humans it was modified for language.

Definitional problems

As with any construct its validity starts with definition. Both Barrett and Sapolsky (p.23) agree that there are definitional issues with triune brain.

• There is no accepted definition of what the 'limbic system' is
• You can still experience emotions with parts of your limbic system missing
• There is considerable overlap amongst the three layers of triune brain
• Information doesn't just flow from the 'limbic system' to the neo cortex but both ways
• Emotional and rational thinking are not separable

These definitional issues have led to neuroscientists to suggested the limbic system is "a non-empirical explanatory concept for poorly understood brain functions" (Kotter & Meyer 1992 p. 105).

Neuroscience helps

In addition to anatomical issues, we know from neuroscience that emotions do not reside in the amygdala or anywhere because:

1. they are concepts we have made up
2. they consist of lots of different ingredients e.g. what we feel, our context, our history & the language we use to describe how we feel etc.

The current consensus is that emotions are not ‘hardwired’ but socially constructed.?

So, there is no ‘lizard brain’ circuitry that automates a ‘fight or flight’ responses to specific stimuli such as fear.?We might want to run fast for lots of reasons – catching a bus, 100m sprint or run from a sabre tooth tiger.?The same sympathetic nervous systems is used but its use is not exclusive to one emotion or one part of the brain.?Our brain functions overlap. For example our brainstem is also used for perception, cognition & emotion (Nishijo et al., 2018) and our prefrontal cortex is involved in not just receiving emotional input from the amygdala but also sending information for emotional processing?to other areas of the brain.

So from a neuroscientific basis the triune brain theory doesn't help understand the origins of our emotions or our reaction to them.

The Verdict

If previous advocates of the triune brain (such as Daniel Goleman) start to distance themselves from it maybe it is time for us to?

I find it curious that Sapolsky uses the triune brain distinction as a foundation in his book but happily dismisses the brain bilateralisation (left v right brain distinction) myth (p.30)

As with any simplification there are advantages & disadvantages. Is it ok, like Sapolsky, to use simplifications at a metaphorical level to ease learning? He openly highlights the dangers of the oversimplification leaving us to explore further.

But without this caveat, oversimplifications create a mental model on which we start to 'hook' all learning which then becomes an axiom for understanding. For example, if our emotions do not reside in our 'limbic system' then trying to 'control' that region as Daniel Goleman suggests won't help.

This simplistic thinking might lead us to think that a cure for anxiety caused by organisational change is simply to think happy thoughts and regulate your emotions better.?But anxiety is just a concept and maybe we should start to understand its underlying drivers i.e., too much prediction error and how we help people with that e.g., create achievable goals, build efficacy, create supportive relationships etc.

Like other myth beliefs such as Change Curve, Brains Hate Change, Sense Of Urgency etc, simplified views that have intuitive appeal but become problematic when they form the basis of our knowledge base and damage how we understand people’s journey through organisational change.

As Cesario et al 2020 suggest that although highly intuitive (because this is the way our learning has been 'wired') this neuromyth

lack(s) any foundation in our understanding of neurobiology or evolution and should be abandoned by psychological scientists.

The triune brain makes us believe that the brain evolved to make us rational or happy rather than to monitor and manage allostatic load.

So wouldn't dumping these myth-beliefs, or at least caveating their limitations, help create a more effective practice where we better understand people's journey though organisational change?

An Alternative?

Rather than pursuing Goleman's ‘emotional intelligence’ and trying to rein in your inner beast (reptile) to regulate our emotions we could start by cultivating emotional granularity by learning how we feel in different situations and understanding why we feel that way.

Lisa Feldman Barrett in her book ‘How Emotions Are Made’ suggest that by becoming more emotionally literate we can fine tune our emotions to particular situations.?Not only does this this make our understanding our emotions easier but also helps our brains to better predict our emotions reducing our predictive error or surprise with how we are feeling (or should feel).

Moving away from controlling to understanding emotions will help people express why they feel anxious about change and as change practitioners we can start to address the causes of those feelings.