Caffeine may help long-term memory
Whether it's a mug full of coffee, a cup of hot tea, or a can of soft drink, consuming caffeine is the energy boost of choice for millions who want to wake up or stay up. But the popular stimulant could also be used as a memory enhancer, according to researchers from John Hopkins University.
The research, published on 12 January 2014 in the journal Nature Neuroscience, showed 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 Michael Yassa, Assistant Professor of Psychological and Brain Sciences at John Hopkins University, and one of the authors of the study. "We report for the first time a specific effect of caffeine on reducing forgetting over 24 hours," he said.
Study method
The researchers conducted a double-blind trial in which participants who did not regularly eat or drink caffeinated products received either a placebo or a 200-milligram 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 session. On the test, some of the visuals were the same as those from the day before, some were new additions, and some were similar but not the same.
More members of the caffeine group were able to correctly identify the new images as "similar" to previously viewed images rather than 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," Professor 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.
Memory and the brain
The memory centre in the human brain is the hippocampus, a seahorse-shaped area in the medial temporal lobe of the brain. The hippocampus is the "switchbox" for all short- and long-term memories. Most research done on memory — the effects of concussions in atheletes, of war-related head injuries, and of dementia in the ageing population — has focused on this area of the brain.
Caffeine after study ensures only memory is measured
According to the John Hopkins University researchers, caffeine's effects on long-term memory had not been examined in detail. Of the few studies done, the general consensus was that caffeine had little or no effect on long-term memory retention.
The John Hopkins University study is different from prior experiments, the researchers said, because the subjects took the caffeine tablets only after they had viewed and attempted to memorise 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," Professor Yassa said. "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," he said.
According to the US Food and Drug Administration (FDA), 90 per cent of people worldwide consume caffeine in one form or another. In the US, 80 per cent of adults consume caffeine every day. The average adult in the US has an intake of about 200 milligrams — the same amount used by Professor Yassa and his colleagues in the study — or roughly one cup of strong coffee per day.
Professor Yassa's team completed the research at John Hopkins University before his lab moved to the University of California, Irvine, at the beginning of 2014.
"The next step for us is to figure out the brain mechanisms underlying this enhancement," Professor Yassa 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," he said.
The lead author of the paper is Daniel Borota, an undergraduate student in Yassa's lab who received a Provost's Undergraduate Research Award from Johns Hopkins to conduct the study.
Additional authors, all from Johns Hopkins, are: Elizabeth Murray, a research program coordinator in the Department of Psychological and Brain Sciences; John Toscano, professor in the Department of Chemistry; Gizem Kecili, a graduate student also in the Chemistry Department; and Allen Chang, Maria Ly, and Joseph Watabe, all undergraduates in the Department of Psychological and Brain Sciences.
The research was supported by grants number P50 AG05146 and R01 AG034613 from the National Institute on Aging as well as CHE-1213438 from the National Science Foundation.
