咖啡因能否促进记忆？

AUDIE CORNISH, HOST: Most of us know what it feels like to have a little caffeine in our system. A cup of coffee wakes us up, gives us a bit of a buzz. Well, it turns out caffeinated nectar does something similar for honey bees. That's the finding of a new study published in the journal Science, as NPR's Allison Aubrey reports.

ALLISON AUBREY, BYLINE: It's too early in the year to expect to see honey bees, says researcher Phil Stevenson, especially from his perch at Royal Botanic Garden at Kew, just outside London.

PHIL STEVENSON: That's right. I mean, I've seen a couple of queens from but will be colonies around, but no honey bees as of yet. Yes, it's still a bit chilly for that.

AUBREY: But it won't be long. And Stevenson says when the bees start foraging for food in spring, they take long flights in search of nectar and then haul it back to their hives.

Now it turns out some of this nectar actually contains caffeine. Not just the nectar of coffee plants, but also citrus plants - including lemons, and oranges. So Stevenson and his colleague were curious. They wanted to know if this caffeinated nectar influenced the behavior of bees. So they designed a study.

STEVENSON: And in this study, you can train bees to associate a reward of food with a smell. It's a little bit like Pavlov's dog. When Pavlov rang the bell, the dog salivated. In this case, when the bee detects the smell, it extends its proboscis.

AUBREY: The smell came from flowers, the proboscis is the bee's long, hairy tongue used to suck up the nectar.

Now, in the study, Stevenson wanted to see whether the bees would respond differently to flowers that contained a caffeine rich nectar, compared to those that just had sugary nectar.

STEVENSON: We found that when they were taking sugar nectar with caffeine, they were three times better able to remember the flowers a day later than bees that were feeding on to sugar alone.

AUBREY: So could this mean that a caffeinated bee has a better memory?

STEVENSON: That's exactly what the study shows. We were very surprised by it, but obviously we were also very excited because it shows that bees are better able to remember a flower. And, of course, for bee this makes it better able to locate food.

AUBREY: Which is obviously a big plus in life.

Now, some researchers wonder if bees simply prefer caffeinated nectar. But whether it's improving their memories were making them more motivated to seek it out - it's intriguing that caffeine can be giving these the same kind of buzz that people get.

ABRAHAM PALMER: Caffeine absolutely influences our behavior. It changes mood and performance in a variety of different ways.

AUBREY: That's Abraham Palmer of the University of Chicago. He says due to genetic differences, our individual responses to caffeine vary. But studies show that caffeine does work on our brain's reward system, and in moderate doses can help improve attention and performance on all sorts of mental and physical tasks. Some of the best studies come from the U.S. military, where caffeine has been studied as a way to keep soldiers alert.

Researcher Harris Lieberman explains he studied a group of sailors who were training to become Navy SEALs.

HARRIS LIEBERMAN: During one portion of that training, they are substantially sleep deprived and exposed to a variety of other stressors.

AUBREY: Including cold temperatures and demanding physical activities. Lieberman says when he compared the sailor who consumed caffeine compared to those who had a non-caffeinated placebo, he documented range of benefits.

LIEBERMAN: We found that in moderate doses, caffeine enhanced ability to pay attention, it enhanced vigilance.

AUBREY: And it seemed to improve the exhausted sailors' short-term memories, something Lieberman was not expecting to see.

LIEBERMAN: We were somewhat surprised that caffeine had such widespread effects.

AUBREY: But Lieberman says, in the absence of exhaustion, caffeine doesn't seem to help people remember any better. So he doesn't think that caffeine is much of a memory booster.

LIEBERMAN: No, I don't.

AUBREY: But whether it's humans or those bees, there's clearly something about caffeine that keeps us coming back for more. Allison Aubrey, NPR News.