ARI SHAPIRO, HOST:
Get cut off in traffic and you might feel angry for the rest of the trip. The experience leads to an emotional response. NPR's Jon Hamilton reports on a new study of how this process may happen in the brain.
JON HAMILTON, BYLINE: As a psychiatrist at Stanford University, Dr. Karl Deisseroth thinks a lot about how people navigate their emotions.
KARL DEISSEROTH: The thing about emotion is it generalizes. It puts the brain into a broader state.
HAMILTON: So anger at another driver can mean you snap at a noisy child in the back seat. Deisseroth and a team of scientists set out to recreate this sort of experience in the lab.
DEISSEROTH: We wanted something that would cause negative emotion but wouldn't be painful.
HAMILTON: They chose a puff of air delivered to the cornea. Deisseroth says the experience is like getting a glaucoma test at the eye doctor.
DEISSEROTH: It's certainly annoying, certainly aversive but not painful. And we thought this also might be something that another mammal would respond to in the same way.
HAMILTON: They tried it on mice. Sure enough, both mice and people blink reflexively in response to a puff. Repeated puffs cause both species to maintain a squint in self-defense. Next, the team studied the brain activity associated with these experiences, and they found two distinct phases involving different areas of the brain. The first phase is fleeting...
(SOUNDBITE OF PIANO PLAYING STACCATO NOTE)
HAMILTON: ...Like a staccato note on the piano. During this phase, which lasts a fraction of a second, there's a spike in the activity of brain circuits that process sensory input. After that, activity moves to other circuits, including those involved in emotion. And this phase lingers...
(SOUNDBITE OF PIANO PLAYING SUSTAINED NOTE)
HAMILTON: ...Like a sustained piano note. Deisseroth says that with each successive puff of air, the response got stronger.
(SOUNDBITE OF PIANO PLAYING REPEATED STACCATO NOTES)
DEISSEROTH: You don't need too long for profound effects to be felt. You just need it to be sustained long enough to merge with and interact with other notes that come after. And from our perspective, this is exactly what emotion means.
HAMILTON: In people, the stronger the brain response, the more they squinted, and the more annoyed they were by the experience.
DEISSEROTH: And the mice, although we don't get those verbal reports, we saw the same self-protective gesture and we saw this crucial generalization in that it made them less likely to seek out rewards.
HAMILTON: Like food, which is a sign that an animal is stressed. To confirm the finding, the team did the experiment again. But this time, both mice and people received ketamine, an anesthetic that disrupts the brain's processing of sensory information. On ketamine, mice and people would still blink reflexively after a puff of air, but they didn't squint. And Deisseroth says the second phase of brain activity was gone.
DEISSEROTH: If you remove this sustained phase, you block the emotion. You block the emotional response as well.
HAMILTON: The study appears in the journal Science. Lisa Feldman Barrett, a professor of psychology at Northeastern University, says it clearly shows how an experience can affect a creature's underlying mental state. But she says sustained activity in certain brain circuits doesn't necessarily indicate an emotion.
LISA FELDMAN BARRETT: Sure, that happens in emotion, but it also happens in all kinds of other instances that we experience as other kinds of mental states.
HAMILTON: Like remembering or paying attention. Barrett also thinks the air puffs probably mean something different to a mouse than to a person.
BARRETT: The human brain has this capacity to abstract, to create meanings that go beyond sensory and motor differences.
HAMILTON: Barrett adds that her concerns about this study extend to many others involving the brain states that influence human and animal behavior. The underlying problem, she says, is that scientists still don't agree on how to define an emotion.
Jon Hamilton, NPR News.
(SOUNDBITE OF AMIE BLU SONG, "EVERYTHING ABOUT HER") Transcript provided by NPR, Copyright NPR.
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