The first irrefutable proof that caffeine enhances memory and can enhance memory as long as 24 hours after consumption was published in the Jan. 12, 2014, edition of the journal Nature Neuroscience by a team of scientists led by Michael Yassa, assistant professor of psychological and brain sciences in the Krieger School of Arts and Sciences at Johns Hopkins University.
The research is considered exclusive proof that caffeine improves long-term memory because all participants in the study received a 200 milligram pill of caffeine after they had seen a series of photographs. This change in experimental design eliminated the potential that the memory effect was due to increased effect on vigilance, focus, and attention that can be produced by caffeine.
The test participants were selected from people who did not regularly use any kind of caffeinated beverage. The test subjects were divided into two groups. Each individual watched the same series of photographs. One group received a 200 milligram pill of caffeine five minutes after seeing the photographs and the other group received a placebo. Caffeine levels were measured in each participant at one, three, and 24 hour intervals after taking the caffeine.
Both groups of participants watched a second set of photographs that had a few different photos and some very similar photos compared to the set of photographs that the participants viewed 24 hours earlier.
More members of the group that took the caffeine could distinguish the added photos and the similar photos. This behavior implies the involvement of a higher level of memory called pattern separation. The memory enhancement lasts as long as 24 hours after consuming caffeine.
All memory involves the hippocampus. The exact mechanism that caffeine has on memory retention has not yet been elucidated.
The researchers indicate that the fact that 200 milligrams of caffeine has been proven to enhance memory should not be taken as a license to consume extreme amounts of caffeine.