Swiss researchers at the University Hospital of Basel gave a group of healthy men either a beverage containing 27.5g of green tea extract or a placebo drink. Next, the men completed a series of tasks designed to gauge their working memory, while the researchers examined their brain activity using magnetic resistance imaging. Overall, the green tea drinkers performed better on the memory tests than the placebo group. The MRIs revealed the parietal lobe (which processes sensory information into words and thoughts) and the frontal lobe (responsible for decision making and problem solving) were better able to communicate with each other. Basically, by increasing the amount of back-and-forth between these two brain regions, green tea boosted these subjects' ability to remember information.
The fact that green tea offers cognitive benefits may not be all that surprising; however, that it can enhance memory so quickly is notable.