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[] His experiments suggest that our sensory organs pass information to the thalamus, where signals split and trace two separate paths on their way to the amygdala, the brain’s threat center.

Following the shorter path, one signal manages to sound the fear alarm before we’re even aware of the situation.

The other reaches the sensory cortex a fraction of a second later, providing a much clearer picture of the potential threat.

The second signal can reinforce the fear response or declare a false alarm.

First, the sensory organs – our eyes, ears, tongue, nose and skin – pick up cues from our surroundings and feed them to the brain.

The brain’s threat center, a structure called the amygdala, is constantly on the lookout for danger. If it identifies a possible threat, it sounds the alarm, immediately kicking the fight or flight response into gear.

These changes are controlled by a part of the peripheral nervous system called the autonomic nervous system, which regulates automatic changes to the body's vital functions.

If an emotional event becomes too traumatic, however, it can negatively affect memory. Researchers have also found that even though people report vivid recollections related to flashbulb memories, they often swear by details that are in fact erroneous.

Scientists can reliably produce fear in the lab through a process known as fear conditioning. Conditioning has provided researchers with an important tool for tracing fear in the brain. After all, before they can study fear and its effects, scientists have to know, with confidence, that what they're looking at is actually fear.

If a researcher plays a loud noise while flashing a light, her subjects will quickly come to pair the flash with the negative experience of the loud noise. Later, the subjects will demonstrate measurable fear of a flash of light, even without the loud noise.

Such associations are reversible through a process called extinction. For example, if the same subjects are shown soothing images while the lights flash, they can eventually dissociate the flashes from the negative experience of the loud noises.

Some scientists believe thrill-seeking daredevils get more enjoyment out of such fear-inducing activities because their levels of a neurotransmitter called dopamine increase more than normal during such experiences. The result can be a feeling of pleasure or euphoria.

Our brains may be unable to distinguish a difference between truly frightening experiences and those that people have purposefully designed to make us feel fearful. This opens the door for scary activities, such as horror movies, haunted houses and roller coasters, which allow us to experience fear without (hopefully) ever risking true physical danger.