Your reptilian brain, explained | Robert Sapolsky | Big Think

What's the best way to think about the brain? It's insanely complicated; everything connects to everything. Amid all that complexity, functionally, it's very easy to think of the brain as coming in three functional layers. This is a broadly simplifying way to think about aspects of brain function when it comes to behavior. This is highly schematic; the brain really doesn't come in three layers.

But one can think of the first most, the bottom most, the most ancient as being what's often termed the reptilian brain. We've got the same wiring as in a lizard, as in any ancient creature. Ancient, ancient wiring at the base of the brain. 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, releasing hormones that are essential to sort of everyday shopkeeping. It's just keeping regulatory stuff in balance.

Sitting on top of that is the limbic system, the emotional part of the brain. This is very much a mammalian specialty. They're off there in the grasslands, butting heads with somebody else with antlers, and it's your limbic system that's heavily involved in having to do with fear, arousal, anxiety, sexual longings—all those sorts of things.

Then sitting on the top is the layer three, the cortex. The most recently evolved part of the brain. It's the part of the brain that does impulse control, long-term planning, emotional regulation. It's the frontal cortex that whispers in your ear saying, "Do you really, really wanna do that right now?" Functionally, it's very easy to think of this simplistic flow of commands.

Layer two, the limbic system, could 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 cut; something painful, but an emotional state. You're a wildebeest, and there are some scary, menacing wildebeest threatening you, and that emotional state causes your limbic system to activate the reptilian brain, and your heart beats faster.

And 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 the layer 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. You see a movie that's emotionally upsetting. These are not real characters; they're pixels, and it's your cortex that's turning that abstract cognitive state into an emotional response.

Likewise, your cortex, layer three, could influence events down in layer one. A purely cognitive state: Ooh, on the other side of the planet, there are people undergoing some traumatic event, and I feel upset about it. And your reptilian brain responds. So it's very easy, given that, to think of a three talks to two talks to one sort of scenario. Just as readily though, one talks to two talks to three.

What's your reptilian brain talking to your cortex? Remarkable finding: when we're hungry, we make harsher moral judgments about people's transgressions. We're less charitable; we cheat more in economic games. Our cortex assessing the effects of pro-sociality, anti-sociality, and part of what it's doing in deciding how it feels about somebody else's plight is if your stomach's gurgling, if you're hungry, if you're in pain, that affects very cortical judgment-type areas.

Layer one, this ancient reptilian brain, that should have nothing to do with how your cortex works, having tons to do with it. Or layer two influencing layer three, your limbic system. Your emotional state influences your abstract cognitive processes. What's the most obvious example of it? When we're under stress, we make stupid impulsive decisions that seem brilliant at the time.

It's embedded in the biology of all of these layers. This interaction between these layers seems like it's a very mechanical process, potentially even an unconscious one. How do we consciously have, say, our cortex regulate an emotion, a limbic two layer? Simple: think about the most arousing, wonderful thing that ever happened to you umpteen decades ago, and your cortex is evoking a memory that's got your limbic system humming along in some excited state.

Or pull out the memories of some traumatic event, and your limbic system is responding. A lot harder is the inverse. You're sitting there, and you suffer from high blood pressure. They can marinate you in antihypertensive drugs for the rest of your life, or an alternative approach, a biofeedback approach.

The core of biofeedback is figuring out what sort of conscious states you can evoke that will affect your reptilian brain in a direction that's good for your health. The biofeedback approach is: sit there and think about the happiest day of your life. Think about being in a beautiful open field. Think about your favorite vacation.

Think about, think about, and if it's the right thinking about, suddenly your heart slows down; suddenly your blood pressure goes down. And all you do then is learn how to get better and better in some stressed hypertensive circumstance. What conscious active thinking can I mobilize here at this point that will cause changes in how my big toe's blood flow is working?

In a case like that, that is very conscious regulation of more autonomic, more ancient parts of your brain.

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