The neocortex, which evolved relatively recently, is located on the surface of the brain. Proportionally, this level occupies more space in the brains of primates than in those of other animal species. Cognition, memory storage, sensory processing, abstraction, philosophy, self-reflection — all reside here.
Read a terrifying passage in a book, and level 3 will signal level 2 to make you feel fear, which in turn will instruct level 1 to initiate trembling. Watch an Oreo commercial, and you’ll feel the urge to eat it — that’s level 3 influencing levels 2 and 1.
Think about the fact that your loved ones (or children in a refugee camp) won’t live forever, or that the tree of the Na’vi in Avatar was destroyed by those awful humans (even though — wait, the Na’vi aren’t real!), and level 3 will engage levels 2 and 1, making you feel sorrow, with a stress response as if you were running from a lion.
This region evolved later and developed in mammals. MacLean explained that this level is associated with emotions — a kind of mammalian invention. If you witness something brutal and horrifying, the neural structures at this level send a signal to the ancient level 1, making you tremble with emotion. If you’re heartbroken over unrequited love, areas here nudge level 1 to trigger cravings for unhealthy food. If you’re a rodent and hear a cat, neurons in this region push level 1 to initiate a stress response.
The ancient component of the brain — its foundation — is present across a range of species, from humans to geckos. This level controls automatic regulatory functions. If body temperature drops, this part of the brain responds by instructing the muscles to shiver. If blood glucose levels fall, it’s detected here too, triggering the sensation of hunger. If a person experiences an injury, another neural center at this level initiates a stress response.
Attention! These are NOT literal layers of the brain.
Let’s begin by examining the macro-organization of the brain. For this, we’ll use a model proposed in the 1960s by neuroscientist Paul MacLean. His “triune brain” model describes the brain as having three functional domains:
So, our brain is divided into three functional blocks, with the usual advantages and disadvantages that come with categorizing any continuum. The biggest drawback is its excessive simplification.
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Level 1:
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Level 2:
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Level 3:
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Anatomically, there is significant overlap between these three levels (for instance, one part of the cortex could be considered part of level 2 — more on this later).
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The flow of information and commands doesn’t just move top-down, from level 3 to 2 and 1. One strange and interesting example we’ll explore in Chapter 15: if a person is holding a cold drink (temperature processed by level 1), they are more likely to perceive a new acquaintance who approaches them as a “cold” person (level 3).
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The automatic aspects of behavior (in simplified terms — the domain of level 1), emotions (level 2), and thinking (level 3) are inseparable.
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The triune model gives the misleading impression that evolution simply stacked one level on top of another, without any changes to the ones that already existed.
Despite all its flaws — which MacLean himself acknowledged — this model will serve as a useful organizational metaphor for us.
When cognitive load on the prefrontal cortex is increased, subjects eventually become less inclined to engage in prosocial behavior, such as charity or helping others, and more inclined to lie. When the load is increased specifically through tasks requiring constant emotional regulation, participants are later more likely to cheat on their own diets. (Source: Inzlicht and Marcora, “The Central Governor Model of Exercise Regulation Teaches Us Precious Little About the Nature of Mental Fatigue and Self-Control Failure,” Frontiers in Psychology 7 (2016).)
Damage to certain areas of the cortex due to a stroke can block the ability to speak; yet some patients manage to convey their cerebral world of language through alternative emotional, limbic pathways — they can sing what they want to say. The cortex and the limbic system are inseparable because numerous neural fibers connect them. Importantly, these fibers ensure a bidirectional communication: the limbic system “talks” to the cortex, not just obeys it. The false dichotomy between thought and feeling is exposed in the classic work Descartes’ Error by neurologist Antonio Damasio of the University of Southern California.
Willpower isn’t just a metaphor — it’s the work of the brain’s frontal cortex, which consumes a tremendous amount of energy to function. Its activity is marked by an extremely high level of metabolism and the activation of genes involved in energy production. Self-control is a finite resource. That’s why tasks requiring this part of the brain become much less effective after something like a shopping spree.
- : Involved in executive functions, such as working memory, cognitive control, planning, and reasoning.
- : Associated with decision-making, particularly in the context of risk and reward, as well as emotional regulation and social cognition.
The ventromedial prefrontal cortex (vmPFC) is a part of the prefrontal cortex in the mammalian brain. The ventral medial prefrontal is located in the frontal lobe at the bottom of the cerebral hemispheres and is implicated in the processing of risk and fear, as it is critical in the regulation of amygdala activity in humans. It also plays a role in the inhibition of emotional responses, and in the process of decision-making and self-control. It is also involved in the cognitive evaluation of morality.
The dorsomedial prefrontal cortex (dmPFC or DMPFC is a section of the prefrontal cortex in some species' brain anatomy. It includes portions of Brodmann areas BA8, BA9, BA10, BA24 and BA32, although some authors identify it specifically with BA8 and BA9. Some notable sub-components include the dorsal anterior cingulate cortex (BA24 and BA32), the prelimbic cortex, and the infralimbic cortex.
