WATCH: The Science of Fear

My favorite horror movie is Evil Dead. It's hilarious, ingenious, and it can still make me jump if the room is dark enough and the volume is turned up enough. I'll probably watch Ash and his chainsaw take on his zombified fellow campers tonight while I intermittently pass out Halloween candy to the few neighborhood kids whose parents still let them go trick-or-treating.

Because I am a skeptic, not a lot of things scare me. But if the horror movie or haunted house is good enough, I will try my best to suspend disbelief. In the right context, though, I enjoy being afraid. We all do. That's why Halloween is so fun.

Fear is an emotion that we usually perceive in a negative light. Fear is necessary for survival. If our ancestors had not been afraid of dangerous situations, they would not have known to avoid them, and we would not be here right now. But researchers Eduardo Andrade and Joel Cohen have shown that we can exploit this fear for pleasure if we realize that we are not actually at risk of any real danger. If we measure the risk of harm against our bodies' adrenaline-laden responses, we are often happy to be afraid, simultaneously experiencing positive and negative emotions. Of course, children are sometimes unable to make this distinction, and their fear response to haunted houses, hayrides, and horror movies may be one of genuine fright.

The beginnings of our fear experiences transpire like most other environmental phenomena: through our sense organs. Sensory experiences are transduced into neural phenomena and quickly make their way to the thalamus, a way station for sensory and motor information that sits between the cerebral cortex and the midbrain. After they reach the thalamus, these signals can follow one of two paths: a fast pathway immediately finds its way to the amygdala, and the slower pathway stops for processing by the sensory cortex.

Interestingly, this dual-pathway system for emotional memory encoding was demonstrated long before scientists had a way to measure the exact brain mechanisms underlying it. In 1911, Edouard Claparede was working with a patient who had Korsakoff's syndrome. Korsakoff's is an amnestic disorder characterized by an inability to encode new memories. It happens after years of heavy alcohol abuse damages the mamillary bodies of the hippocampus, a brain structure necessary for forming new memories. (As an aside, if you haven't already read The Man Who Mistook His Wife for a Hat by Oliver Sacks, I highly recommend it. The second story, The Lost Mariner gives a beautiful account of a patient with Korsakoff's.) Anyway, in order to test whether or not Dr. Claparede's patient could form implicit memories, he shook her hand with a hidden pin in his palm and pricked her upon his introduction. The next time he entered the room, although she had no memory of ever meeting him, she withdrew her hand when he extended his. A fear memory had been formed without her conscious awareness.

The amygdala is an almond-shaped structure found deep within the temporal lobe that is responsible for encoding strong emotional memories, like fear (fear-laden memories are specifically encoded in the basolateral nucleus of the amygdala). The sensory cortex is a portion of the brain that receives and processes sensory information, often giving us a conscious awareness that we have seen, heard, smelled, tasted, or touched something. Because the fast fear pathway hits the amygdala first, we often have the sensation of being afraid before we realize what it is that we are actually afraid of.

Once the brain has processed a stimulus and recognized it as fearful, it sets off an endocrine alarm system. This is initiated by a branch of the autonomic nervous system called the sympathetic nervous system, otherwise known as the fight-or-flight response. We experience this whole-body phenomenon when we must be quick on our feet, reacting to a potential predator. Of course, there is no real predator when we are watching a horror movie from the living room sofa, but our sympathetic nervous systems don't know the difference.

During fight-or-flight, the glands that sit atop our kidneys, known as the adrenals, release epinephrine (adrenaline). In addition, our heart rate quickens, breathing shallows and speeds, pupils dilate, and some of us uncontrollably sweat. We also experience two symptoms that are almost synonymous with Halloween: goosebumps and trembling. Goosebumps are actually the result of a phenomenon called piloerection, wherein small muscles in the skin cause our hairs to stand up on end. We feel in on the back of our necks. We see it on our arms and legs. It is thought that this is a somewhat vestigial response, dating back to when our ancestors were extremely hairy. When their hairs stood on end, they probably looked more fierce to predators and could potentially scare them away. We still see it today in our pets, most notably the famed Halloween cat. Also, when we're scared, we literally shake in our boots. This is because our body shunts a lot of that oxygenated blood to our legs so that we can run away as fast as we can. But if we are standing still, that increased muscle tension causes us to shake.

This Halloween, think about what's actually happening to your brain and body when you are shaking with fear!

You can learn more about the science of fear with your kids (or on your own, if you're a big kid, like me) at the California Science Center's Goosebumps: The Science of Fear exhibit, which will also be traveling to cities across the USA.

Happy Halloween!

*In a previous version, the word adrenaline was mistakenly replaced with serotonin. This has been corrected.

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