Zombie Olfaction: Smells Like Undead Spirit

If you’re preparing for the zombie apocalypse, you might want to read up on olfaction—the undead are known to rely on their sense of smell.

| October 2014

  • Misty cemetery
    Olfaction is the only sense with a direct route from sensory cells to the brain, which may explain the tight connection between flashbulb memories, like those you might create were you attacked by a zombie while walking through the cemetery, and scent.
    Photo by Fotolia/AlienCat
  • Do Zombies Dream of Undead Sheep?
    “Do Zombies Dream of Undead Sheep?” by Timothy Verstynen and Bradley Voytek is an engaging exploration of characteristic zombie behavior from a neuroscientific perspective.
    Cover courtesy Princeton University Press

  • Misty cemetery
  • Do Zombies Dream of Undead Sheep?

Timothy Verstynen and Bradley Voytek take on the neuroscience of the zombie brain in Do Zombies Dream of Undead Sheep? (Princeton University Press, 2014) with witty analyses of the characteristic lumbering gait, insatiable hunger for brains and memory-less existence of the undead. Through this exploration they shed light on fundamental neuroscientific questions while bringing in examples from zombie popular culture. The following excerpt from Chapter 6, “There’s No Crying in the Zombie Apocalypse!” deals with how olfaction works in the healthy brain—and how it applies to evading zombies.

Listen, Do You Smell Something?

How do you smell? Not, like, how stinky are you right now, but how does your sense of smell work and why does that connect so strongly with certain emotions? The smell of your grandmother’s house when she’s baking cookies; the smell of the perfume or cologne of the person you love; the scent of rot and decay of the undead beasts hunting you down: why do these smells move you?

First, we must understand how olfaction, our sense of smell, works. Our senses include vision, touch, hearing, balance, taste, and smell, all of which somehow combine into a unified percept that informs us about ourselves and the world around us; but of these, only taste (gustation) and smell (olfaction) require us to directly, chemically sample our world. This can be a dangerous bargain given the number of toxic and noxious chemicals out there.

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Ultimately we only become aware of a sensation when it enters our explicit consciousness. From a neuroscientific point of view this translates into a stimulus activating a set of neurons in the nose that in turn send signals to an early sensory area called the olfactory bulb that in turn send signals to the more cognitive parts of the neocortex where they are registered into awareness. But often there are many steps that allow for processing of these sensory signals even before they reach the neocortex. This fact means that, in rare cases of brain damage, someone can react to stimuli without even being aware of them. The classic example is blindsight, where people who are technically blind can respond to certain visual inputs without being aware of doing so. Individuals with blindsight will swear they don’t see objects in the room, but when asked to walk around can somehow avoid obstacles on the floor that would otherwise make them trip.

Beyond Blindsight

This ability to use sensory information (without necessarily being consciously aware of it) happens because every sense, except for one, passes first through a neural gatekeeper just before entering our neocortex. This neural gatekeeper is the thalamus, which sits atop our brainstem and helps modulate the sensory input before the input enters our awareness. The one outlier sense that doesn’t pass through the thalamus is smell. Instead, olfactory input goes directly into our neocortex, particularly to the cortical areas that process both emotion and memory. This fact is thought to underlie the strong link between smells and memories, which they can trigger even after many years have passed—for example, when the smell of freshly baked cookies reminds you of your grandmother, or when the rancid smell of rotting flesh reminds you of your first run-in with an undead walker.

While we may have a direct link between the sense of smell and the more cognitive areas of the brain, it doesn’t mean that we in fact use olfaction as a primary sense when interacting with the world. That privilege appears to be restricted to our visual and auditory senses. In fact, humans are often thought to have a relatively terrible sense of smell, especially compared to our canine friends. This is why we’ve spent millennia training and domesticating dogs to help us hunt; us humans seem to have a terrible time finding a buffalo based on its smell!

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