The tall and the short of why caffeine works.

Byline: Ronald Kotulak

Dec. 1--Caffeine is the most widely used stimulant in the world, consumed in coffee, tea and soft drinks by hundreds of millions of people to get started in the morning and as a pick-me-up during the day. That people like the jolt they get from caffeine is no secret, but what caffeine does in the brain has been unknown.

Now a team of Austrian researchers using advanced brain imaging technology has discovered that caffeine makes people more alert by perking up part of the brain involved in short-term memory, the kind that helps focus attention on the tasks at hand.

And Americans seem most in need of concentrating their thoughts, since their average daily consumption of 236 milligrams of caffeine, equivalent to more than 4.5 cups of…