Illustration for article titled Why Do Zombies Shuffle?

This headline isn't the set up for a joke (although I obviously welcome your punchlines in the comments); it's a real question. Is there a neuroscientific basis for the prototypic zombie's lumbering gait?


Neuroscientists Timothy Verstynen and Bradley Voytek wrote Do Zombies Dream of Undead Sheep? to provide readers a neuroscientific view of the zombie brain. Slate has published an excerpt from the book, in which Versteynen and Voytek give us the lowdown on zombie brain (dis-)function:

Let's consider the following scenario: You're a zombie sitting very patiently on the examination table, hand resting on your desiccated, disgusting lap. The nerdy scientists in their awkward lab coats then place a tasty chunk of human flesh right in front of you. What remains of your undead frontal lobes will immediately say "GO GET THAT!" because, hey, free thigh.

Before you can actually grab that tasty piece of meat, however, the motor planning areas in your undead brain, called premotor regions, have to figure out how to get your hand from your lap to the yummy flesh. Now remember, while you can see the tasty morsel, the process of getting your hand off of your lap and to the chunk of meat is pretty complicated. Somehow your brain has to convert a map of the world that's being projected from the back of your eyeballs to a plan of muscle contractions that uses your bones as levers, much as a puppet master has to coordinate the strings of a marionette doll to make it dance—except here the puppet master is your own brain.

Let's return our attention to that horde of walking dead outside. While zombie movements are slow, stiff, and uncoordinated, zombies do seem to be able to plan movements in the right direction. That is, when a zombie wants to lunge toward you, it mostly gets the direction right. Once it gets its hands on you, it has no problem grasping and holding on. Therefore it would appear that the cortical motor systems are all intact. So what could be wrong? The only real neural culprits left as plausible candidates for the motor dysfunction seen in zombies are the basal ganglia and the cerebellum.

Given this restriction, let's consider what happens when the basal ganglia are malfunctioning and compare that with when something goes wrong with the cerebellum. In both cases, people have trouble walking and coordinating their movements, but in dramatically different ways. For example, in Parkinson's disease, people develop a slouched posture and walk by taking short, shuffling steps. They also have difficulty generating actions without a very obvious goal (they tend to freeze up). In contrast, people with spinocerebellar ataxia develop a stiff, wide-legged stance and take big, lumbering steps. And unlike those afflicted with Parkinson's disease, these patients have no problem initiating movements.

How can we use this information to diagnose a zombie's brain? We know that the walking dead are shown in movies as having a stiff, wide-legged stance and a big, lumbering walk. They tend to move slowly (most of the time) and lack smooth, coordinated actions. Yet they don't seem to have trouble initiating movements. In fact, zombies are almost constantly on the move, they never have problems starting a movement (say reaching for a new victim), and they don't stall in the middle of movements. They also don't shuffle or have curvature in their posture.

For these reasons we argue that the cluster of symptoms seen in zombies, the wide stance, lumbering walk, lack of freezing, ease in general planning and execution of actions, reflects a pattern of cerebellar degeneration. That is, cerebellar dysfunction would lead to many of the motor symptoms of the zombie infection. However, cortical motor areas and basal ganglia pathways should be relatively intact.


But what about fast-moving zombies? Verstynen and Voytek have an explanation for that, too. Check it out over at Slate.

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