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!
Dr. Timothy Verstynen & Dr. Bradley Voytek of the Zombie Research Society are posting a series entitled The Living Dead Brain: What Forensic Neuroscience Can Tell Us about the Zombie Brain. I think you will find it relevant to your interests.
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