What is the science behind fear?

Fear is an adaptive behavior that we have to help identify threats. It is an ability that has allowed us as humans to survive predators and natural disasters. We are born with only two innate fears: the fear of falling and the fear of loud sounds.

A 1960 study evaluated depth perception among 6- to14-month-old infants, as well as young animals. Researchers placed the subjects on a platform that had plexiglass just beyond its edge to it to see how many of the subjects would actually step over the "visual cliff." Most of the subjects -- both children and animals -- didn't go "over" and step out on to the plexiglass. The fear of falling is an instinct necessary for the survival of many species.

When you hear loud sounds, you most likely will react with a fight or flight type response. It's called "your acoustic startle reflex," said Seth Norrholm, a translational neuroscientist and faculty member of the NS program at Emory University.

Most fear is learned. Spiders, snakes, the dark -- these are called natural fears, developed at a young age, influenced by our environment and culture. So a young child isn't automatically scared of spiders, but builds on cues from his parents.

When presented with something that scares you, your brain reacts with its fight or flight response. For example, if you see a snake while hiking, there are two roadways for your brain, said Norrholm.

First is the low road that represents your brains sensory systems in the brain's amygdala. It's "what you see, smell, hear," and signals to the brain that this is something to fear. It's the adrenaline response that tells your heart to beat faster and your body to sweat.

Almost simultaneously, there's a high road reaction. "That goes through your higher cortical center in you brain. The high road says 'I've seen this kind of snake before, and I don't have to worry'," said Norrholm. Think of it as the reasoning response that overrides the low road.

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