3 Brain Systems That Control Your Behavior: Reptilian, Limbic, Neo Cortex | Robert Sapolsky

3 Brain Systems That Control Your Behavior: Reptilian, Limbic, Neo Cortex

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You have three brains—the triune, the limbic, and the cortex—and they're all fighting for dominance as you go about your life. The so-called lizard brain (the triune) is perhaps the one we tend to think of as instinctual and gives us our basic instincts like, for example, staying alive or not touching fire. The limbic brain controls our emotions like fear and desire, while our cortex gives us the knowledge that makes us human. Basically, the three brains talk to one another and vie for rank in certain situations... it's sort of like Three's Company except with brain systems. For instance: you're reminded of something sad by your cortex and it triggers your limbic system, or you get cut off in traffic your lizard brain can trigger the cortex and the limbic. It is a pretty fascinating subject, and Robert Sapolsky waxes poetic about the three distinct "characters" that live up inside your head.

Robert Sapolsky's most recent book is Behave: The Biology of Humans at Our Best and Worst.

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ROBERT M SAPOLSKY:

Robert M. Sapolsky holds degrees from Harvard and Rockefeller Universities and is currently a Professor of Biology and Neurology at Stanford University and a Research Associate with the Institute of Primate Research, National Museums of Kenya. His most recent book is Behave: The Biology of Humans at Our Best and Worst.

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Transcript:

ROBERT SAPOLSKY: What’s the best way to think about the brain? It’s insanely complicated. Everything connects to everything. A gazillion little subregions.

Amid all that complexity there’s a broadly sort of simplifying way to sort of think about aspects of brain function when it comes to behavior. And this was an idea put forth by this guy Paul MacLean, a grand poohbah on the field, conceptually of thinking of the brain as coming in three functional layers.

The triune brain—and again this is highly schematic—the brain really doesn’t come in three layers, but one could think of the first most, the bottom most, the most ancient as being what’s often termed the “reptilian brain,” where basically the parts in there, we’ve got the same wiring as in a lizard, as in any ancient creature. It’s been there forever—ancient, ancient wiring at the base of the brain, most inside. And what does that region do? All the regulatory stuff. Your body temperature changes, it senses it and causes you to sweat or shiver. It’s monitoring your blood glucose levels. It’s like releasing hormones that are essential to sort of everyday shop keeping. It’s just keeping regulatory stuff in balance.

Sitting on top of that is conceptually what could be termed the limbic system, the emotional part of the brain. And this is very much a mammalian specialty. Lizards are not well known for their emotional lives. Part of the brain having to do with fear, arousal, anxieties, sexual longings, all those sorts of things – very mammalian. You’re off there in the grasslands butting heads with somebody else with antlers, and its your limbic system that’s heavily involved in that.

Then sitting on the top is the layer three, the cortex. The cortex, spanking new, most recently evolved part of the brain. Everybody’s got a little bit of cortex but it’s not until you get to primates that you’ve got tons, and then apes, and then us. So functionally it’s very easy to think of this simplistic flow of commands. Layer two, the limbic system, can make layer one, the reptilian brain, activate. When is that? Your heart beats faster not because of a regulatory reptilian thing—Ooh, you’ve been caught in something painful but oh, an emotional state. You’re a wildebeest and they’re some scary menacing wildebeest threatening you and that emotional state causes your limbic system to activate the reptilian brain and your heart beats faster. You have a stress response. Not because a regulatory change happened in your body but for an emotional reason.

Then it’s very easy to think of, layered on top, this cortical area commanding your second layer, your limbic system to have an emotional response rather than something emotional: Here’s a threatening beast right in front of you. Something emotional. You see a movie that’s emotionally upsetting. See a movie. These are not real characters. They’re pixels and it’s your cortex that’s turning that abstract cognitive state into an emotional response.

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