“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,” says Michael Yassa, assistant professor of psychological and brain sciences at Johns Hopkins University.
The Yassa team’s paper – published January 12, 2014 in the journal Nature Neuroscience – shows “for the first time a specific effect of caffeine on reducing forgetting over 24 hours,” he says.
Yassa and colleagues, led by undergraduate Daniel Borota, gave research participants a series of images to study, and five minutes later gave them either a 200-milligram caffeine tablet or a placebo. The subjects—none of whom regularly ate or drank caffeinated products—provided saliva samples before taking their tablets to measure their caffeine levels. Saliva was taken again one, three, and 24 hours later.
The next day, the caffeine group and controls were tested on their ability to remember the images from the previous day. Some of the visuals were the same, some were new and some were similar to but not the same as those the subjects had studied. More members of the caffeine group were able to correctly identify new images as “similar” to previously viewed images versus erroneously citing them as the same.
The brain’s ability to recognize the difference between two similar but not identical items reflects a deeper level of memory retention, the researchers say.
Timing the caffeine
“If we used a standard recognition memory task without these tricky similar items, we would have found no effect of caffeine,” Yassa says. “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 hippocampus, a seahorse-shaped area in the brain’s medial temporal lobe, is the switchbox for short-term and long-term memories. Most research done on memory—from the effects of concussions in athletics to war-related head injuries to dementia in the aging population—is focused on this area of the brain.
Until now, caffeine’s effects on long-term memory had not been examined in detail. From the few studies done, the general consensus was that caffeine had little or no effect on long-term memory retention.
The research is different from prior experiments, however, in part because the subjects took the caffeine tablets only after they had viewed and attempted to memorize the 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,” Yassa says, “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.”
According to the US Food and Drug Administration, 90 percent of people worldwide consume caffeine in one form or another. In the United States, 80 percent of adults consume caffeine every day. The average adult has an intake of about 200 milligrams—the same amount used in the Yassa study—or roughly one strong cup of coffee or two small cups of coffee per day.
Yassa’s team completed the research at Johns Hopkins before his lab moved to the University of California, Irvine, where he is a visiting faculty member, at the start of this year.
“The next step for us is to figure out the brain mechanisms underlying this enhancement,” he says. “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.”
The lead author of the paper is Borota, who received an undergraduate research award from Johns Hopkins to conduct the study. The National Institute on Aging and the National Science Foundation also supported the study.