Researchers at the Johns Hopkins University in US have found the first clear evidence that caffeine enhances certain memories for at least up to 24 hours after it is consumed.
"We've always known that caffeine has cognitive-enhancing effects, but its particular effects on strengthening memories and making them resistant to forgetting has never been examined in detail in humans," said Michael Yassa, assistant professor of psychological and brain sciences in the Krieger School of Arts and Sciences at Johns Hopkins.
"We report for the first time a specific effect of caffeine on reducing forgetting over 24 hours," said Yassa, senior author of the paper.
In the study, participants who did not regularly eat or drink caffeinated products received either a placebo or a 200-milligramme caffeine tablet five minutes after studying a series of images.
Salivary samples were taken from the participants before they took the tablets to measure their caffeine levels.
Samples were taken again one, three and 24 hours afterwards.
The next day, both groups were tested on their ability to recognise images from the previous day's study session. On the test, some of the visuals were the same as from the day before, some were new additions and some were similar but not the same as the items previously viewed.
More members of the caffeine group were able to correctly identify the new images as "similar" to previously viewed images versus erroneously citing them as the same.
The brain's ability to recognise the difference between two similar but not identical items, called pattern separation, reflects a deeper level of memory retention, the researchers said.
"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," he said.
"The next step for us is to figure out the brain mechanisms underlying this enhancement. We can use brain-imaging techniques to address these questions," Yassa said.
"We also know that caffeine is associated with healthy longevity and may have some protective effects from cognitive decline like Alzheimer's disease. These are certainly important questions for the future," Yassa added.
The study is published in the journal Nature Neuroscience.