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Increased heart rate. Hyperventilation. Tense muscles. Clammy hands. Dry mouth. Trembling. Dilated pupils. Goose bumps. Immobility. All are common symptoms of a certain emotion; fear.
It’s common knowledge that Halloween and horror movies just naturally go together. As the end of October approaches, the local Redbox becomes more popular and settling down to watch Netflix requires not only a bag of popcorn, but also a warm, comfy blanket. From creepy mirror disappearing tricks to scenes of reanimated children, there is a never-ending supply of horror movies ranging from pathetically predictable to satanically scary. However, have you ever thought of what exactly causes fear and why is it so addictive?
Fear, like happiness, somberness, and anger, is an emotion. Emotions are an autonomic or involuntary response triggered by patterns that are recognized by the brain such as a mixture of colors or a sequence of sounds. Fear specifically is a fight-or-flight response that includes involuntary body adjustments, such as increase in heart rate, and voluntary movement, such as fleeing or hiding. It is caused by a situation that is perceived as dangerous or risky. This situation is the start of a series of neurological events.
The pathway to fear begins with sensory receptors that receive information of touch, taste, smell, sight, and hearing. In the case of a horror movie, detected images travel through the optic nerve in the eyes and sounds travel through the auditory nerve in the ears as electrical impulses to the thalamus, a structure near the middle of the brain. Since the thalamus doesn’t have the ability to judge the amount of danger the situation possesses, the impulses are sent to two other locations in the brain; the sensory cortex and the amygdala. The sensory cortex interprets the meaning of sensory information and the amygdala determines if a fight-or-flight responses is needed to protect the body. In the scenario of hearing a noise outside your bedroom window, the sensory cortex runs through possible sources of the noise while the amygdala automatically perceives the noise as a burglar. Of the two brain structures, the sensory cortex is slower at processing information than the amygdala. This accounts for why you feel terror for a moment before you can calm down. From the sensory cortex and amygdala, electrical impulses are sent to the hippocampus. The hippocampus uses its memory of previous sensory information to review the sensory information one last time before deciding to trigger a fight-or-flight response.
A fight-or-flight response requires the sympathetic nervous system. When the sympathetic nervous system is activated, it sends out impulses to multiple glands which release over 30 different hormones, including epinephrine from the adrenal glands. Together, the hormones cause changes in the body. Increased heart rate, tense muscles, constricted veins, the shutdown of nonessential processes (such as digestion), and dilated pupils all indicate the end of the fear process.
Most modern humans don’t have to constantly fight for their lives or run from danger, but fear still functions the same in humans and animals from thousands of years ago. Whether you’re saving yourself from a speeding car or burrowed under blankets in front of a scary movie, I hope that you’ll stop your trembling to consider the biological process of fear.