You light up my life, eyes, face, brain

When you're in love, your eyes light up, your face lights up and, apparently, so do four small parts of your brain.

"It is the common denominator of romantic love," said Andreas Bartels, a doctoral student at University College, London, who presented his research at a Society for Neuroscience conference in New Orleans in the United States.

He used functional MRI (magnetic resonance imaging), a scanning device that shows the brain over time instead of a still picture, to examine 17 students who said they were truly in love and whose statements were backed up by psychological tests.

When the subjects were shown photographs of their sweethearts, different areas of the scan image lit up indicating higher blood flow than when they were shown photographs of friends.

The friends were the same sex as the sweethearts and were people the subjects had known for about the same length of time.

Any number from six to 20 parts of the brain showed increased activity, varying from person to person, but only four were found as a common denominator in all 11 women and six men, Mr Bartels reported.

The specific areas that lit up were part of the anterior cingulate cortex, which is near the brain's midline, and, deeper in the brain, the middle insula and parts of the putamen and caudate nucleus.

Mr Bartels said that looking at pictures of their loved one reduced activity in three larger areas of the brain known to be active when people were upset or depressed. "The images are clear but the emotions aren't," said Dr Marcus Raichle, of Washington University.

"The brain scan images do show a common reaction but the question is: what is the state that is being elicited?"

While there were plenty of rating scales for anger and fear, Dr Raichle said, love had not been as thoroughly studied.

Similar scales to those used for negative emotions were needed for love, he said.

Mr Bartels said the lack of previous research was what interested him.

"Vast numbers of studies have been done on negative emotions: fear, sadness, anger, disgust. We decided to test a positive emotion."