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(Zombie noises) Doctor 1: So, here we are again.
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You know, I've been thinking. Why is this thing so angry?
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Doctor 2: Maybe he's just hungry.
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D1: (Laughs) I'm not going in there to feed it.
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No, this seems like something very primal.
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D2: This is kind of a hard one,
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because we don't really have any biological definitions for emotions like anger.
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Sure, brain imaging studies have shown that some brain regions are more active when people are angry,
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but these are almost always correlational.
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When it's warmer outside, people wear less clothing,
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but if I strip down to my birthday suit, it doesn't make it sunny.
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D1: (Laughs) It's like having someone run on a treadmill and saying
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"Look at how much more his arms move when he runs faster!
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The arms must be where running happens."
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D2: That's why working with people with brain lesions is so important to neuroscience.
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It adds some causal evidence that a brain area might be required for a behavior.
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Same with brain simulation studies.
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If stimulating a brain area causes a behavior,
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then that's good evidence that the brain region is involved in that behavior.
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So like studies with cats in the 1950s
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showed that stimulating a small almond-shaped area deep in the brain called the amygdala
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leads to aggressive or predatory behaviors.
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These things look pretty aggressive to me.
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D1: Right. But other studies have shown that stimulating different parts of the amygdala
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can actually suppress predatory behaviors.
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So it's kind of a complicated little brain structure.
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D2: Yeah. And fMRI studies have found that the amygdala is active in violent criminals.
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D1: Whoa, whoa, whoa. Careful there.
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Just because criminals have the same active brain regions as people who are angry,
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doesn't mean that they're inherently aggressive.
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That's like saying because I kiss with the same face hole that I use to burp,
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then these two things are related.
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It's a false equivalence.
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D2: Huh! Never thought of it like that. That's a good point.
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D1: You know, the amygdala is part of the Papez circuit.
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This system was discovered by James Papez, who used the rabies virus to lesion different areas in the cat's brain.
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He found that the amygdala was physically connected to another region called the hippocampus --
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a little seahorse-shaped area that is needed to turn short-term memories into long-term memories.
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It's thought that this connection between the amygdala and hippocampus
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links emotion and memory together,
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so that you remember really emotional stuff better than boring everyday things.
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D2: Yeah, like Patient H.M. In the 1950s, surgeons removed both his left and right hippocampuses
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to treat his epilepsy.
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But after the surgery, he couldn't remember any new information for longer than a few minutes.
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Zombies appear to be pretty forgetful, wouldn't you agree?
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D1: (Laughs) Absolutely. Between the amygdala-related aggression,
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and memory deficits from the hippocampus,
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Papez may have actually accidentally created the first zombie cat.
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D2: Aw, come on now, let's not get carried away.
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But now we do have some testable hypotheses.
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