The first systematic study investigating the effects of caffeine on human performance – sponsored by Coca-Cola – has been published about 100 years ago. Since then, thousands of other studies have been looking at if and in which ways caffeine improves cognitive performance. This question is still debated in science, but there is general consensus that caffeine can be seen as an enhancer for specific functions like mood, attention, concentration and reaction time. These enhancement effects have been shown in studies with the general set-up that participants first took caffeine and then did a performance task. This matches our everyday representation of “wise” caffeine use: if I wanted to enhance my performance with caffeine, I’d take it immediately before the “critical situation”, for example an exam.
It has been claimed previously that caffeine also enhances memory. However, the studies investigating this question followed the above reasoning: caffeine had been given to participants before they did a memory task. Hence, when improved performance in this task was found, it was difficult to determine whether this was actually due to enhanced memory, or rather due to a boost of other functions like mood or concentration. So it has been unclear whether caffeine enhances memory or not.
A new study published in Nature Neuroscience sheds light on this question: in a double-blind, placebo-controlled trial, researchers around Michael Yassa from Johns Hopkins University asked their participants to study a series of images. Some minutes after this study phase, participants were given 200 mg of caffeine – a dose that equals about one large cup of coffee. The next day, participants were again presented with images, some of which were the same as the ones they had seen the previous day, some were new but very similar, and some were clearly different. Compared to the placebo group, participants who had taken caffeine the day before were better in distinguishing new but similar pictures from those previously seen. Hence, caffeine was found to enhance long-term memory consolidation, the process of stabilising memories. The main novelty of this study is that caffeine was administered after the study phase. As Michael Yassa explains in a short video: “All of the past studies have always administered caffeine before somebody would study the material … so it’s not clear whether it’s enhancing their focus, their attention, their vigilance or enhancing their memory for the material they study. Giving caffeine after the study phase has never been done in human studies before … you exclude all of the other effects that are non-memory.”