Most babies can start sensing pain a few weeks before they are born, according to a new British study. The researchers found that babies react to pain signals by tightening their muscles and releasing stress hormones. They also noted that babies seem to prefer softer sounds and smells after being exposed to pain signals.  There has been a long-standing debate about whether or not babies feel pain when they are born. For years, doctors have argued that newborns don't feel pain because their nervous systems aren't fully developed. However, this new British study suggests that babies can start sensing pain a few weeks before they are born.  For the first time, researchers at Oxford University have observed infants' brains react to the light prodding of their feet. And researchers have found that babies do feel pain and that they process it similarly to adults.  Until as recently as the 1980s, scientists believed newborns lacked fully developed pain receptors, and any responses the babies showed to pokes and pricks were merely muscular reactions.