When we must return to a task after interruption or delay, our brain's working memory tries to retain the necessary information. We use this form of memory, say, to keep a telephone number in mind just long enough to dial it. But working memory has a short life and limited capacity. About four items is the most it can hold. If we start a conversation before we dial the phone number, the number will disappear.


Working memory is so fugitive in part because it is encoded in the activity of brain cells. As we try to remember a new phone number, neurons in our frontal and parietal lobes are firing away. (By contrast, the long-term memory of, say, where we last parked our car is encoded in the strength and topography of connections between neurons in the occipital and temporal lobes.) Attention works the same way: Neurons increase their activity as we concentrate on an object or task, and they slow their firing when something else intervenes. It is true that the brain can accomplish many things at once (we can drink coffee and listen for a train station to be announced while we read the morning paper), but it can only pay careful attention to one at a time. Indeed, attention is so precious that it is easily depleted -- even when the added task (such as talking on a cellphone) superficially seems to be completely independent of the primary one (driving a car).

For Mr. Klingberg, the mismatch between our modern lives and ancient brains is most evident in the problems of working memory and attention, but another culprit may be at work. We are easily distracted also because we vastly overvalue what happens to us right now compared with what comes in the future and because novelty is intrinsically rewarding. So whatever we are supposed to be focusing on has to compete with every new email, new task, new blog post and new conversation that wanders into our information sphere. These biases may have served us well in our species' evolutionary past, when the future was uncertain and the new could well be a threat that deserved immediate attention. But nowadays the new is more often trivial than essential, and sacrificing immediate rewards can yield greater ones in the future.

What to do? Mr. Klingberg details how he and other brain researchers are trying to find ways to increase mental capacity. Many doctors already recommend various brain-boosting activities, from crossword puzzles to aerobic exercise, for staving off Alzheimer's disease. Nintendo's "Brain Age" games claim to improve the brain with various puzzle-tasks. Although some claims have notoriously failed to hold up (research showed that listening to Mozart's music would not in fact increase IQ), the field is young, and there is no reason to believe that the inherent plasticity of the brain cannot be stretched further. It is hard to say, though, whether it will ever stretch far enough to manage the email that has built up in my inbox since I started writing this review.