Most of the zombies you see on television and in movies moan and groan, and pull and tear, and lumber and shuffle, and remain highly focused on finding braiiinns to eat. But why do zombies act the way they do? They suffer from Consciousness Deficit Hypoactivity Disorder, an ailment coined by Timothy Verstynen and Brad Voytek.
“We are tricking people into learning neuroscience and history of neuroscience by talking about zombies,” says Verstynen, an assistant professor in the psychology department at Carnegie Mellon University in Pittsburgh (knowing that Pittsburgh-native George Romero filmed Night of the Living Dead in the area had just a little to do with him moving there). The two presented the neuroscience of zombies at ZombieCon in 2010 and produced a presentation for TEDEd about it.
As any consumer of pop culture knows, a zombie's main characteristic is its drive to eat human flesh. Verstynen and Voytek say that if they really existed, zombies would be hungry because they have lost some hypothalamic functioning, which controls satiety. People with this kind of damage eat and drink nonstop. “Zombies are constantly trying to eat people because they are never full,” Verstynen says. And they can only focus on the immediate problem—and if that means the food is moving, then zombies are hungry.
These shuffling undead have terrible attention spans and can only focus on what’s right in front of their faces, likely due to damage in their parietal lobe. They experience something like the real-life Bálint's syndrome, which renders sufferers only able to see the thing that requires the most attention. They observe the person running across the room, not the group of zombie hunters standing in the corner. In case you ever find yourself facing a zombie, keep this in mind: It’s actually better to stop and hide than try to run, Verstynen says.
When the zombies ruthlessly hunt people, they walk with a specific gait, wide-legged and lumbering, thanks to spinocerebellar ataxia. This movement disorder, caused by damage and atrophy in the cerebellum, contributes to an awkward, halting walk with slurred speech and balance problems. When the duo met Romero at ZombieCon, they asked him why the zombies moved so slowly, assuming he had an elaborate theory. He simply said that zombies were dead so he thought they’d walk stiffly.
Fast zombies, as seen in 28 Days Later or World War Z, move with such speed because they took less time to resurrect, what Verstynen and Voytek call the resurrection hypothesis. “Fast zombies themselves have less brain damage than the slow ones,” says Verstynen. It’s similar to hypoxia, when the brain is deprived of oxygen. The longer one goes without oxygen, the more damage she will have.
Another notable zombie trait is the inability to recognize anyone from its former life. That’s because zombies suffer from prosopagnosia, otherwise known as face blindness. And damage to the hippocampus causes retrograde amnesia, making every day seem the same. Zombies possess no long-term memories.
“Zombies are very impulsive and have emotional disruption,” Verstynen says. But this differs from their inability to remember. The duo suspects that if they existed, zombies would have injured Papez’s circuits, a neural highway that connects the amygdala, hippocampus, and limbic system in the brain, and helps with the creation of emotional memories. This damage also means it’s harder for zombies to control their angry impulses.
On top of this rage, zombies can’t verbally express their angst because of a flawed arcuate fasciculus, which connects two regions of the brain responsible for language. Because Broca’s area fails, zombies can only groan and grunt (and possibly mumble “brains”) while damage in Wernicke’s area makes it impossible for them to understand pleas of mercy from their victims.
While the zombie brain has a lot of problems, Verstynen notes their senses and motor control remain intact. “We wanted the science to be 100 percent real,” Verstynen says. He and Voytek, an assistant professor at the University of California, San Diego, have been working on a book on the history of neuroscience and the neuroscience of zombies, which Princeton University Press will publish next year.