What's the difference between anxiety and panic? Your brain knows, though until now many scientists didn't. Recent research by Wendy Heller shows that the two states originate in different cerebral hemispheres—and that previous research had often confused them.

Scientists studying anxiety had produced conflicting reports of its site in the brain, says Heller, because they failed to distinguish anxious apprehension (worry) from anxious arousal (panic). In an effort to sort out the two, Heller and her colleagues compared the brain activity of a group of people who often felt anxious apprehension and a group who tended toward anxious arousal. Even at rest, the worriers had more left brain activity, the panickers more right.

That makes sense, says the University of Illinois psychologist, because the left hemisphere controls speech production—worrying is primarily a verbal activity—while the right side plays a greater role in regulating panic's physical effects: increased heartbeat, sweating, and production of stress hormones. Heller adds that the brain's distribution of duties offers an extra benefit: When blood flow to a particular region increases, the brain performs better on associated tasks. So some amount of worry sharpens our verbal abilities, and a moderate level of arousal improves our processing of visual and spatial information. "If you're in danger, you will see better and navigate better," says Heller. "The locations of these states in the brain isn't an accident."

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