John Bowlby claimed that attachment serves an adaptive purpose: to keep parents and caregivers close to ensure the child's survival. In the early stages of attachment, babies use social releasers, such as crying, grasping, smiling and gazing, to elicit adults' caregiving; Bowlby believed that adults are innately programmed to respond to these signals. Now research using event-related fMRI ,a technique that shows which parts of the brain are activated in response to specific events, has shown that the reward centres of mothers' brains are activated by their own child's smile, but not by the smiles of other children. The report by Baylor College of Medicine researchers appears in the journal Pediatrics today.