Multitasking.

Despite its amazingness, the brain cannot concentrate on more than one thing at a time. Does this mean you shouldn't multitask? Does it depend on how old you are? It does! But not the way you're guessing it does:

A group of 18- to 21-year-olds and a group of 35- to 39-year-olds were given 90 seconds to translate images into numbers, using a simple code.

The younger group did 10 percent better when not interrupted. But when both groups were interrupted by a phone call, a cellphone short-text message or an instant message, the older group matched the younger group in speed and accuracy.

“The older people think more slowly, but they have a faster fluid intelligence, so they are better able to block out interruptions and choose what to focus on,” said Martin Westwell, deputy director of the institute.

Of course, some of us "older people" are over 39, possibly by quite a few years. I wonder how fast and fluid we are. At some point, we've got to slow down, and at some point, fluidity of the brain is dementia.

Concentration is a funny thing. I don't think you can test it with a single task and a single type of interruption. A younger person may be more easily distracted by an instant message because it has intense emotional associations -- new sexual adventures or emergency demands from bosses.

I know my ability to concentrate and my susceptibility to distractions have changed over time, but I can't sort out what is caused by age and what is caused by changing life circumstances. Am I unwilling to sit in a dark room for two hours and devote myself to watching a movie because I've aged, because blogging has rejiggered my attention span, or because I don't have the right movie buff companion?