Coffee has long been a friend of students working through the night, but it does more than just keep us awake. A study provides the first convincing evidence that caffeine enhances long-term memory in people 鈥� provided the dose is right.
The effects mirror similar results seen in honeybees, where a boost to memory from caffeine-laden nectar may help bees return to certain plants.
Researchers strongly suspected that caffeine enhances memory, but studies that tried to show this in people weren鈥檛 conclusive, as any apparent benefits in memory could have been due to increased attention, a known benefit of caffeine.
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Studies in animals such as rats, meanwhile, suggested that it enhances memory consolidation 鈥� the process of strengthening memories between acquiring them and retrieving them 鈥� which should affect long-term memory.
Seahorse similarity
To investigate further, , a neuroscientist at the University of California, Irvine, recruited 160 adults who normally consume only minimal amounts of caffeine. The volunteers first studied images of objects, before randomly receiving a pill containing either 200 milligrams of caffeine 鈥� equivalent to two espressos 鈥� or a placebo. Receiving the caffeine after studying the images helped to isolate the effect of caffeine on memory, as you wouldn鈥檛 expect alertness to matter at this point.
When the volunteers returned 24 hours later, they took a memory test involving images they had seen before, unseen images and images that were similar but not identical, such as a seahorse with a different shape to one they had seen previously. The volunteers had to classify these as 鈥渙ld鈥�, 鈥渘ew鈥� or 鈥渟imilar鈥�.
Yassa鈥檚 team recorded no differences in accuracy for identifying old or new images between the volunteers who had taken caffeine and those who hadn鈥檛 鈥� but this was expected because this part of the task was so easy.
Too much caffeine
However, the group who had received caffeine were significantly better than the placebo group at identifying which images were 鈥渟imilar鈥� rather than 鈥渙ld鈥�, which Yassa says is a harder task.
He concludes that caffeine enhances long-term memory by improving the process of memory consolidation. 鈥淭his doesn鈥檛 mean people should only drink coffee after they鈥檝e studied, and not before,鈥� says Yassa. 鈥淚 think you would get the boost regardless.鈥� That鈥檚 because the process of consolidation is likely to begin as soon as new memories form.
However, caffeine isn鈥檛 much use once consolidation is finished. The team ran a second experiment in which caffeine wasn鈥檛 administered until one hour before the memory test, to check for any effects on memory retrieval. They found no such effect. 鈥淪o let鈥檚 say you studied without coffee and decided to drink a cup right before an exam 鈥� that鈥檚 not going to help you retrieve memories better,鈥� says Yassa.
Caffeinated bees
The results have impressed of Newcastle University, UK, who last year showed the link between caffeine and long-term memory in honeybees.
鈥淲e were often asked: what are the implications for humans?鈥� says Wright. 鈥淪o it鈥檚 nice someone actually did the experiment and found evidence that caffeine has a direct effect on memory consolidation.鈥�
Finally, Yassa鈥檚 study also revealed that the dose of caffeine is important. When they repeated the experiment with 100 milligram and 300 milligram doses they found that neither was significantly different from placebo. This could be because other effects kick in at higher doses that negate the benefits for memory consolidation. Also, participants given the 300 milligram dose reported side-effects like jitters and headaches, says Yassa.
Wright鈥檚 team found a similar effect in bees. 鈥淚n high concentrations it looks like [caffeine] is bad for learning 鈥� so don鈥檛 drink too much!鈥� says Wright鈥檚 colleague Julie Mustard at Arizona State University in Phoenix.
Journal reference: Nature Neuroscience, DOI: 10.1038/nn.3623
