Be sure to visit The Cognitive Axon tomorrow for symptom 2!
Symptom 1: Impulsive-reactive aggression
It’s pretty much a given that zombies are constantly pissed off and they want to eat you. The snarls, the teeth, the guttural howls as they close in on their prey... these creatures are enough of a public health danger and menace to warrant serious research funding from the National Institutes of Health!
The adrenalin-infused rage of thousands of raging beasts is unmistakable.
So what does this uncontrolled, rampant rage tell us about the zombie brain? First, the type of rage that zombies exhibit is of a very primal form known as impulsive-reactive aggression. This is more like the aggression you see when two drunks get in a fight.
It differs from the cold and calculated rage seen, for example, in a school shooting. The zombies will direct their anger at anyone and everyone simply because they're human. This type of rage has its roots in the more “primitive” (i.e., phylogenetically older) parts of the brain and reflects the engagement of the “fight-or-flight” circuitry that all mammals have. Steve Schlozman has referred to this circuit as the "crocodile brain".
Normally, these every-day anger impulses are suppressed by signals that originate in the lower part of the frontal lobe: the orbitofrontal cortex. This area sends inhibitory signals to the medial amygdala, a little almond-shaped area that sits at the front of your temporal lobe. If left uncontrolled this tiny region would ramp up signals to the hypothalamus and thalamus that trigger the adrenal responses you feel when angry and frightened. But since most of us have an intact orbitofrontal cortex, the little amygdala is turned down except in rare cases.
Studies of violent, pathological criminals have found that functional abnormalities of the dorsal and ventral prefrontal cortices and the amygdala may underlie some anti-social and violent behaviors. Furthermore, people with damage to the orbitofrontal cortex often have issues with social cognition, understanding and adhering to social norms and mores, as well as moral decision-making.
Some of you may have heard of the famous case of Phineas Gage who had a rod shot through his brain and went from mild-mannered middle management to uninhibited risk-taker and speaker of all things inappropriate. Well that’s because he lost his orbitofrontal cortex.
Certainly the zombie doesn’t care about social norms or morality!
Given the impulsive and aggressive behavior exhibited by zombies, it’s safe to say that they
lack a properly functioning orbitofrontal cortex. So we’ve modeled the zombie brain such that the orbitofrontal cortex is more or less obliterated. As a result, the zombie amygdala, hypothalamus, and thalamus (specifically the bed nuclei of the stria terminalis) should be constantly overactive. These changes would easily produce a hair-trigger adrenal response unlike anything seen in normal humans!