Lots of people who are extremely skeptical of herbal medicines rely on one every day. It changes their metabolism, increases their focus, and alters their bodies in a variety of ways. It's called caffeine, and in many ways it's a wonder drug. Now, researchers have added yet another item to the list of things caffeine can do: it helps consolidate memories.
The team behind this work, based at Johns Hopkins and University of California-Irvine, says that teasing apart the effects of caffeine is challenging. "The general consensus among past studies is that caffeine has little or no effect on long-term [memory] retention," they write. But those studies are complicated by the fact that the caffeine is usually administered with a sufficient lead time to make sure it's having an impact while people are doing their memorizations. In those circumstances, all the other effects of the drug—"increased arousal, vigilance, attention, and processing speed"—can also influence the degree to which memories are formed.
To avoid this issue, the researchers didn't administer the caffeine until after participants had performed an image memorization task. Twenty-four hours later, they tested their memories with a mixture of images: some were the ones from the day before, some were completely new, and some were similar to the previous ones—called lures, they were meant to tax a user's memory.
There was no difference between the placebo and caffeinated groups on basic memory; they were equally likely to know when they had seen an object before or when it was new. (Incidentally, the caffeinated group was just as likely to guess they were controls as the placebo group was.) The difference came when they were exposed to the lures. Here, caffeine-treated individuals were more likely to correctly identify something as similar rather than the same as an item they'd seen the day before.
The authors were also able to show that there could be a dose effect, with the effects of caffeine plateauing at about 200 mg. That's one or two cups of coffee, or four cans of Mountain Dew. The dose effect was also reflected in the amount of caffeine metabolites found in the saliva. This particular experiment, however, only tested three different doses, so more work will be needed to have confidence in the results.
The authors argue that this suggests that beyond all the other effects it might have on the immediate process of memorization, caffeine can also enhance the consolidation of memories. Although the memories themselves are formed during exposure, the brain takes some time to lock them in place (or, alternately, discard them). If that process isn't successful, the brain is more likely to discard the specific memory while retaining a more general sense of familiarity. By pushing the process toward consolidation, caffeine favors the formation of distinctive memories.
There are a number of potential biochemical mechanisms that could explain how caffeine intervenes in the process of solidifying memories. However, on a practical level, it's now clear that it's easier to justify a late-night espresso when exam time comes around.
Nature Neuroscience, 2014. DOI: 10.1038/nn.3623 (About DOIs).
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