Narrator:        This is Science Today. Most people are able to gradually accept the loss of a loved one and move on with their lives. But for a substantial minority, it's impossible to let go. This is called "complicated grief" and a UCLA study has found that it activates neurons in the brain related to reward centers. Psychiatrist Mary-Frances O'Connor, who led the study, explains.

O'Connor:      Those we love, when we are with them, we feel pleasure, we enjoy that and when we lose someone, we have to adapt to the new reality that the reminders of those people - pictures, memories, things in our home - they no longer will cue us, will bring us to that person. That person will never be back again. And the brain has to adapt to this new information. In those with complicated grief, they are still showing the same reward cue that people do when they are living. So, they haven't adapted to the knowledge that that person is not coming back again.

Narrator:        For Science Today, I'm Larissa Branin.