A jolt of caffeine can boost memory, according to a study published Sunday that provides a scientific motive for students slurping coffee, tea or energy drinks when cramming for exams.
A team at Johns Hopkins University in Baltimore, Maryland, found that caffeine enhances certain memories for at least a day after they were formed.
Evidence for caffeine as a memory booster has been anecdotal until now.
This is because the process of registering memories -- say, reading a book ahead of an exam -- may happen in conditions where the person is eager to absorb and retain information.
This makes it hard to distinguish between someone's natural alertness and that derived from caffeine.
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To strip out this confounding factor, a team led by Michael Yassa, an assistant professor of psychological and brain science, tried a different tack.
They asked 73 volunteers to look at images of a number of objects -- for instance, a plant, a basket, a saxophone, or a seahorse.
Afterwards, half of the group were given a 200 milligramme dose of caffeine -- roughly equivalent to two cups of strong espresso -- and the others a dummy pill known as a placebo.
Saliva samples were taken one, three and 24 hours later to measure caffeine levels.
The following day, both groups were asked to look at another set of pictures.
Some of the images were the same, others were new, and a few were similar -- for instance, a basket as before, but this time with one handle instead of two.
Both groups did well at distinguishing between old and new pictures, the researchers said. But those on caffeine were much sharper at identifying the "similar" items in the lineup.
The test sought to discern the effect of caffeine on the hippocampus, a part of the brain that distinguishes between patterns -- requiring both short- and long-term memory.
"If we used a standard recognition memory task without these tricky similar items, we would have found no effect of caffeine," Yassa said.
"However, using these items requires the brain to make a more difficult discrimination -- what we call pattern separation, which seems to be the process that is enhanced by caffeine in our case."
The study, published in the journal Nature Neuroscience, could be valuable in the study of brain cell health.
"Caffeine is associated with healthy longevity and may have some protective effects from cognitive decline like Alzheimer's disease," said Yassa.
"These are certainly important questions for the future."