The Science of Fear

 To understand the basic tenets of fear, we have to start by looking at the nervous system – specifically, the peripheral nervous system. While the brain and the spinal cord make up the central nervous system (CNS), the peripheral nervous system (PNS) is composed of all the outside stuff – nerves connecting the rest of the body back to the CNS. The PNS has a lot of functions, including regulating involuntary behaviors like heartbeat and digestion.

Within the involuntary portion of the PNS, there are two main subdivisions: sympathetic and parasympathetic. The parasympathetic division works to maintain your bodily functions at rest, saving energy, slowing your heart rate, and facilitating active digestion. That’s why we say the function of the parasympathetic nervous system is to “rest and digest.”

Meanwhile, the sympathetic division is active under stress, when you might need to take flight or prepare to fight. Activity of the sympathetic division includes increased heart rate and inhibited digestion – essentially the opposite of the parasympathetic division. Increased heart rate improves the flow of oxygen-rich blood, making it easier to move your muscles for running or attacking. And you don’t want to poop while you’re fleeing, so inhibited digestion allows your body to focus energy on these more active behaviors.

As you can imagine, the ability to respond to a threat quickly could present an evolutionary advantage, and you might notice some of these functions when someone dressed as a zombie jumps out at you or while you watch your favorite scary movie. You might say your heart skipped a beat, because you felt your pulse suddenly pick up. Or maybe your tummy starts to hurt because you’re not digesting properly.