Get cut off in rush-hour traffic and you may feel angry for the whole trip, or even snap at a noisy child in the back seat.

Get an unexpected smile from that same kid and you may feel like rush hour — and even those other drivers — aren't so bad.

"The thing about emotion is it generalizes. It puts the brain into a broader state," says Dr. Karl Deisseroth , a psychiatrist and professor at Stanford University.

Deisseroth and a team of researchers have come up with an explanation for how that happens.

The process involves a signal that, after a positive or negative experience, lingers in the brain, the team reports in the journal Science.

Experiences themselves act a bit like piano notes in the brain. Some are staccato, producing only a brief burst of activity that may result in a r

See Full Page