Ever wondered why some people are full of "get up and go" and why others drag their heels? Why some kids at school charge enthusiastically around the running track, while others prefer to go for a smoke behind the bike sheds? If work published in Science this week fulfills its promise, there might soon be an answer.

Much of what we know about emotions and feelings -- where they come from and how they are processed -- comes from observations of people with damaged brains. In the front part of the brain is an area that University of Glasgow scientist Graham Cairns-Smith calls the "let's just do it" area. People who suffer damage to this area, called the anterior cingulate, lose initiative and the desire to say or do anything.

Motivation also goes down. People may feel unmotivated after being unemployed for months or years or if stuck in a dead-end McJob -- but it's far worse in stroke patients who have suffered damage to the anterior cingulate. Such people are sometimes able to answer questions but do not talk unless spoken to. On partial recovery, they report that they had lost the will to act -- the "let's just do it" area of the brain had apparently shut down. Even flipping burgers all day leaves you with more motivation that that.