Fear and anxiety are both responses to danger but differ in timing. Fear strikes when something is an imminent threat: a tiger jumps over a fence, lunging at you. Anxiety, on the other hand, occurs when you have a moment to consider a threat: you spot a tiger in the distance and have time to think about whether to run or hide.

New research from Caltech assistant professor of cognitive neuroscience Dean Mobbs, appearing online May 20 in the journal Nature Human Behaviour, shows for the first time how the brains of anxious individuals react to both fast (fear-based) and slow (anxiety-based) attacking threats. The results indicate that most individuals, whether anxious or not, respond to fast threats in the same way. Basically, they run. But when it comes to slow threats, a person's level of anxiety makes a difference: the more anxious they are, the sooner they will flee a dangerous situation.

"If you tell an anxious person that there is a tiger in the building, then they will want to get out fast," says Dean Mobbs. "We can see this in the brain—anxious individuals show faster and stronger activity in the anxiety circuits of their brains when presented with slow attacking threats."

The study builds upon previous work by Mobbs and colleagues that teased apart fear and anxiety circuits in the human brain. In the study, participants were asked to play a "virtual predator" video game while inside a functional magnetic resonance imaging machine that measures brain activity. The participants' goal was to escape attack from the virtual predator. The longer they waited out an impending attack, the more money they earned; if they waited too long and were caught, they received an electrical shock to the hand.