The image of bleary-eyed college students surrounded by cups of coffee or cans of energy drinks used to fuel a late-night study session may not be a representation of the best study habits, but their beverage choice may give them an edge: The caffeine in their drinks is a memory enhancer.

New research from Johns Hopkins University has concluded that caffeine has a positive effect on long-term memory in humans.

Writing in the journal Nature Neuroscience, the researchers report that caffeine enhances certain memories 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 the paper's senior author Michael Yassa, an assistant professor of psychological and brain sciences at Johns Hopkins. "We report for the first time a specific effect of caffeine on reducing forgetting over 24 hours."

For the study Yassa and his colleagues recruited participants who do not regularly consume caffeine. The study subjects were asked to study a series of images, then were given either a 200-milligram caffeine tablet or a placebo tablet five minutes after studying.

The subjects caffeine levels were measured via salivary samples before the study session, and again one, three and 24 hours after the dose was administered.

The following day, the caffeinated group and the placebo group were both tested on their ability to recall the images from the previous day's study session.

During the recall test, some of the images presented were the same ones, some were new additions, and other images were similar but not exactly the same as the items previously viewed.

Most members of the caffeinated group were able to correctly label similar images as such, versus erroneously identifying them as the same.

By being able to recognize the difference between two similar but not identical items, the subjects were demonstrating a deeper level of memory retention known as pattern separation.

"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."

Little research has been conducted on the effect of caffeine on long-term memory. Of the few studies that have been done, the general consensus was that caffeine had little to no effect on long-term memory. One reason the results were different with Yassa's study may have been that the subjects were given caffeine only after they had view and attempted to memorize images.

"Almost all prior studies administered caffeine before the study session, so if there is an enhancement, it's not clear if it's due to caffeine's effects on attention, vigilance, focus or other factors. By administering caffeine after the experiment, we rule out all of these effects and make sure that if there is an enhancement, it's due to memory and nothing else," said Yassa, who conducted the research at Johns Hopkins before moving his lab to the University of California, Irvine at the beginning of this year.

"The next step for us is to figure out the brain mechanisms underlying this enhancement," he said. "We can use brain-imaging techniques to address these questions. 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."