Acrophobia

Thirty thousand slimy yellow wax-worm maggots (baby worms) squirm over the contestant's face into her mouth. Their manure-like stench is stifling, and she gags while using her lips to rummage inside a box. Her challenge: Retrieve as many severed chicken feet as she can before the clock runs out--without using her hands. Whether it's a coffin of scorpions or shark-infested tank, contestants on the hit TV show Fear Factor boldly face their worst fears and compete for a $50,000 cash prize.

How do some people manage to confront such terrors, while others are left paralyzed? Scientists are probing the nature of fear, specifically how the emotion is programmed into the brain, and even how specific genes (basic units of hereditary material) might determine the difference between a wuss and a warrior.

SCI-FRIGHT

All animals have an innate (inborn) ability to fear, and for good reason--survival. Fear of being eaten motivates animals to evade predators. "A system in the brain learns which things are dangerous and we avoid them," says Dr. Gregory Quirk of the Ponce School of Medicine in Puerto Rico. If a snarling dog bit you, for example, you may be afraid of that dog--or all dogs--later on. That's because a memory of the fearful event is stored in the amygdala, a grape-size structure at the base of the brain.

The next time the dog shows up, the amygdala recalls the experience and releases two hormones--chemicals that perform many body functions--into the blood. Epinephrine (also known as adrenaline) and norepinephrine spur the heart to pump more blood to the muscles and prepare the body to either confront or run from a threat--the body's instant fight-or-flight response, Quirk explains.

"The problem is, when you learn to be afraid of something, that memory is always in your brain--it doesn't go away," he says. So how do people overcome a certain dread? Humans form new memories that override the fear, Quirk claims. Recently he discovered that rats use the prefrontal cortex (brain region behind the forehead) to conquer fear. New memories let the cortex send an "all-clear" signal to supersede the fear trigger in the amygdala. The same may also prove true in humans.

Then why are some people more naturally fearful than others? They may possess a weaker connection between the two brain areas that control fear, Quirk speculates. Another possibility: Fearful people possess unique DNA that may render them more likely to learn fear. Columbia University scientist Eric Kandel discovered a gene called GRP that prevents the amygdala from learning fear. Mice without the GRP gene were much more afraid of an electric shock than normal mice. "There may be a genetic predisposition to be fearful and to learn fear," says Kandel. Oh no!

FEARFUL DISORDERS

SPECIFIC PHOBIA: Irrational fear of a particular thing

PANIC DISORDER: Feelings of terror that strike suddenly and repeatedly

SOCIAL PHOBIA: Overwhelming fear of social situations

GENERALIZED ANXIETY: Chronic worry and tension even though there's little provocation

POST-TRAUMATIC STRESS DISORDER (PTSD): Anxiety disorder that develops after exposure to a terrifying event in which grave physical harm was threatened or occurred

ARACHNOPHOBIA: Fear of spiders is one of the most common phobias. But out of 34,000 known species, only 12 are poisonous to humans.

ACROPHOBIA: Fear of heights

SCOLECIPHOBIA: Fear of worms. Fear Factor celebrity contestant Kelly Preston (Jerry Maguire) in a box full of giant African millipedes and stinging superworms.

BELONEPHOBIA: Fear of needles, pins, and other sharp objects

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