According to XConnect:
Coffee and donuts may not be the best breakfast for your waist, but turns out they may actually be good for your brain. According to a study by researchers at the University of Barcelona, the combination of caffeine and glucose may boost your brain in terms of attention and memory. 72 women and men, ages 18 to 25, took part in the study, in which, after fasting overnight, subjects were given doses of water, water plus caffeine, water plus glucose, or water plus caffeine and glucose (similar to what you’d get in two soft drinks). Then they were tested on attention, manual dexterity and memory. Subjects showed improved reaction times if given water spiked with either caffeine or glucose, but the ones with a combination of both showed improved effects on attention and on learning and consolidation of verbal memory. According to researchers, this shows that the coffee-sugar combination made the test subjects’ brains more efficient. Of course the tests probably weren’t run after they crashed from their sugar/caffeine high.