The next day, participants were shown a broader set of imagesand asked to identify which ones were new, old, or similar. The caffeinated group was more likely to recognize slight differences in the pictures, such as a yellow rubber duck that was fatter than the one they’d seen the day before. “Without these tricky similar items, we would have found no effect of caffeine,” University of California, Irvine, neuroscientist Michael Yassa tells Forbes.com. “However, using these items requires the brain to make a more difficult discrimination—what we call pattern separation, which seems to be the process that is enhanced by caffeine.” It’s that form of memory that people use, for example, to recall where they last parked the car.
Caffeine’s effect depends on the dosage, however: Researchers found that 100-milligram tablets didn’t improve memory, while 300-milligram doses caused headaches and jitteriness.