Popular wisdom holds that caffeine enhances learning, alertness and retention, leading millions to consume coffee or caffeinated drinks before a challenging learning task such as attending a business strategy meeting or a demanding scientific presentation. However a new study in the journal Nature Neuroscience conducted by researchers from Johns Hopkins hints that when it comes to long-term memory and caffeine, timing may be everything; caffeine may enhance consolidation of memories only if it is consumed after a learning or memory challenge.

In the study the authors conducted a randomized, double-blind controlled experiment in which 160 healthy female subjects between the ages of 18 and 30 were asked to perform a series of learning tasks. The subjects were handed cards with pictures of various random indoor and outdoor objects (for instance leaves, ducks and handbags) on them and asked to classify the objects as indoor or outdoor. Immediately after the task the volunteers were handed pills, either containing 200 mg of caffeine or placebo. Saliva samples to test for caffeine and its metabolites were collected after 1, 3 and 24 hours.

After 24 hours the researchers tested the participants' recollection of the past day's test. Along with the items in the test ('old') they were presented with new items ('foils') and similar looking items ('lures'), neither of which were part of the task. They were then asked to again classify the items as old, new and similar. There was a statistically significant percentage of volunteers in the caffeinated group that was more likely to mark the 'similar' items as 'similar' rather than 'old'. That is, caffeinated participants were clearly able to distinguish much better between the old and the other items, indicating that they were retaining the memory of the old items much better than the people in the placebo group.

To rule out the effect of caffeine on memory retrieval rather than memory consolidation, the authors also conducted another test in which caffeine was administered 1 hour before a learning task on the second day. This prior administration led to no statistical differences relative to placebo. Different doses of caffeine (100 mg, 200 mg, 300 mg) were also tested and it was found that there was a difference between the results of the 100 and the 200 mg doses but not between the 200 mg and the higher dose. This indicates that while there is a minimum dose of caffeine that may be helpful for memory consolidation, the effects of higher doses will have to be further investigated (many people take much higher doses of caffeine during their typical caffeinated week).

The authors acknowledge one obvious limitation of the study - the possibility that awareness of caffeine ingestion might have affected memory consolidation; however they found an even split between participants who thought they had ingested caffeine and those who thought they had been administered a placebo.

The authors conclude:

Numerous studies in animals have shown that caffeine has neuroprotective effects5, 6, 7, 8. Prior work also found a positive effect of post-training administration of caffeine on consolidation of memory9. Notably, a recent study suggests that caffeine in floral nectar may boost memory for reward in honeybees10, suggesting that the mnemonic effects of caffeine may not be limited to mammals. No study to our knowledge has demonstrated a positive effect of caffeine on human long-term memory while excluding nonmnemonic effects. Our results demonstrate that caffeine enhanced consolidation once these effects are appropriately controlled.

They also speculate on various molecular mechanisms through which the caffeine might be acting to enhance memory; it would definitely be interesting to investigate these mechanisms in the future. The small sample size in this study makes it hard to generalize the effects, but the conclusions are definitely intriguing. For now, it may be better to hold off on that cup of coffee until after you attend that new project meeting.

Note: As Mike Yassa, the lead author on the study, pointed out to me, the study did not actually test whether consuming caffeine before a task enhances memory, the problem being that other confounding factors can then lead to difference in performances on the test. The present conclusions are only regarding effects of caffeine administered after a learning task.