Don't take social isolation or loneliness lightly, as brain scans have shown it can be as harmful as smoking.The research, pioneered by the University of Chicago (U-C), is the first to combine fMRI scans with such data to study links between perceived loneliness and brain activity.

Ventral striatum, which is critical to learning, is a key portion of the brain and is activated by primary rewards such as food and secondary rewards such as money. Social rewards and feelings of love also may activate the region.

Conversely, the temporoparietal junction - a region associated with taking the perspective of another person - is much less activated among lonely than in the non-lonely when viewing pictures of people in unpleasant settings.

'Given their feelings of social isolation, lonely individuals may be left to find relative comfort in nonsocial rewards,' said John Cacioppo, psychology professor at the U-C, at a briefing of psychologists.

The subjects who rated as lonely were least likely to have strong activity in their ventral striata when shown pictures of people enjoying themselves, said an U-C release.Although loneliness may influence brain activity, the research also suggests that activity in the ventral striatum may prompt feelings of loneliness, Decety said.