As Halloween approaches our thoughts turn to black cats, dark alleys and being scared. But what is fear all about? We asked David Amaral, director of research at the UC Davis Medical Investigation of Neurodevelopmental Disorders (M.I.N.D.) Institute and expert on fear and social neurobiology. A professor of psychiatry and neuroscience, Amaral studies emotion, memory, learning and social behavior and the neural basis of autism.

What is fear?

Fear probably emerged as one of the earliest emotions. Fear allows us to detect and respond to dangers, and avoid things that could damage us. It's a complicated process. If something novel shows up, your brain needs time to figure out whether the novel object is a danger. Once you've detected danger, there is a change in body systems. Your heart races; you start sweating. But at the same time, your brain is more alert, so you're focusing on the potential danger. Your memory systems work better, so you remember where you encountered that danger and what it's like. Fear is all of those things together.

How do we become fearful?

We are pretty convinced that a few stimuli are innate elicitors of fear. That makes sense -- if we had to learn the concept of danger by experience, we'd lose a lot of individuals along the way. So evolution builds in a couple of primitive fears, and then we add on to them through learning.

How does the brain tell us to be afraid of something?

Let's take the example of detecting a snake in nature. People and monkeys have an innate fear of snakes.

The brain systems involved in detecting a danger include the parts of the brain that allow us to see the snake, such as the visual system. But the visual system is emotionally neutral.

However, from studies in monkeys, we know that if you damage a specific part of the brain called the amygdala, fear vanishes. Monkeys with damaged amygdalas are no longer frightened of a snake: They'll go right up to it and pick it up. It's not that they can't see the snake as a snake. They no longer see the snake as a danger. So we think the amygdala is the place where patterns of danger are detected. Then the amygdala interacts with other brain regions, triggering responses such as escaping.

The amygdala appears to handle innate fear and also learned fears. For example, when you see the police car and realize you're going over the speed limit, that is your amygdala working!

Are there medical conditions caused by fear sensors going awry?

Yes. The most common is the various forms of anxiety disorder. There is evidence from functional magnetic resonance imaging studies that the amygdala is hyperactive in people who have anxiety.

We think the amygdala has a set point or threshold. When you're viewing the environment, certain stimuli exceed the set point, and they really are dangerous, so you should be frightened. Other stimuli are below the set point and shouldn't generate fear. For example, going outside and seeing somebody walking on the street shouldn't be considered a threat. But if you have agoraphobia, fear of open spaces, then the stimulus of just seeing somebody walking by exceeds the threshold.

We think the set point can vary. Probably part of it is genetic. Someone with anxiety disorder may be genetically predisposed to a very active amygdala. But other things could contribute -- a very difficult life situation may reset the amygdala, causing anxiety.

What's new in fear treatment?

Most fear disorders are now treated pharmacologically although psychotherapy or cognitive behavioral therapy can also help. On the horizon are new drugs that will allow your brain to unlearn that certain things are fearful.

Why can it be fun to be scared?

This is a hard question to answer. When you are frightened, you are aroused, your senses are keenly tuned and you get an adrenaline rush. Fright activates all of the primal brain systems that are activated in eat-or-be-eaten situations that our early ancestors experienced. Part of this activation is a sense of relief or well-being that comes about if we are not eaten. So, it is fun for modern people to experience that arousal and then sense of relief that can come from artificial threats like a scary movie or bungee jumping.

-- By Erin Digitale