Problem drinkers have a different brain reaction to alcohol than those who drink socially.

Researchers at the University of California San Francisco studied twelve social drinkers and thirteen heavy drinkers.

All participants underwent PET scans after consuming a measured amount of alcohol. They found an area of the heavy drinkers' brains reacted more positively to alcohol -- which experts say is a sign they have a heightened sense of pleasure when they've had too many.

The area of the brain is called the orbitofrontal cortex.