A study published in Nature Neuroscience by researchers from the Johns Hopkins University, USA has investigated the effects of caffeine on long-term memory in humans.
The highly cited study by Yassa et al reports that previous research has investigated the effects of caffeine as a cognitive enhancer; however its effects on long term memory have not been investigated in much detail. Previous studies have documented that caffeine has little or no effect on long term retention. Using a post study design, the scientists tested the memories of 160 people, who do not regularly eat or drink caffeinated products, over 24 hours.
On the first day of the study the participants were shown images of objects and then received either 200 mg of caffeine or a placebo. After administration of either caffeine or placebo the scientists took salivary samples from the participants at 1 hr, 3 hr and 24 hr to quantify for caffeine metabolites.
Twenty four hours later the scientists evaluated the participants’ recognition performance using some of the objects from the previous day as well as some new items and some that were similar but not identical to ones shown before. Yassa et al state that “identifying these lures as ‘similar’ has been previously shown to be associated with hippocampal activity.” Those who received the caffeine were found to have significant increases of caffeine metabolites at 1 hr and 3 hr after administration. The participants who took the caffeine were found to be better at identifying pictures that were similar, compared to those who took the placebo. However the researchers found that both groups were able to accurately identify whether objects were new or old.
Yassa et al also conducted further experiments to investigate performance with 100 mg and 300 mg of caffeine. They found that compared to the 100 mg performance was better after the 200 mg but there were no improvements after the 300 mg of caffeine compared with 200 mg.
The study notes that although the mechanism by which caffeine enhances memory consolidation remain largely unclear they make an number of suggestions including that by blocking adenosine, caffeine can prevent it from inhibiting a hormone called noradrenaline, which has been shown to have positive effects on memory. Another possibility is “caffeine actions in the CA2 region of the hippocampus, which is largely enriched in adenosine A1 receptors, enhances long term potentiation in this subfield, which may have a role in certain types of memories.”
The scientists do note that caffeine can have side effects and the benefits have to be weighed against the risks.