NEW ORLEANS - When you're in love, your eyes light up, your face lights up - and, apparently, so do four tiny bits 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 Tuesday at the Society for Neuroscience.
He used functional MRI, a brain scan showing 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 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 about as long.
Anywhere from six to 20 parts of the brain showed increased activity, varying from person to person, but only a common denominator of four were found in all 11 women and six men, Bartels said.
In addition, he said, looking at pictures of their loved one reduced activity in three larger areas of the brain known to be active when people are upset or depressed.
The images are clear, but the emotions aren't, said Dr. Marcus Raichle of Washington University, who attended Bartels' presentation Tuesday. The brain scan images do show a common reaction, he said. ''The question is, what is the state he is eliciting?''
While there are plenty of rating scales for anger and fear, Raichle said love has not been as thoroughly studied. Scales like those for the negative emotions are needed for love, he said.
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 tease out a positive emotion.''
In the study, Bartels said the students were asked what they felt when they looked at the pictures, to be sure they were feeling romantic love. The areas of the brain that became active were near areas which also become active when someone is feeling simple lust, but they are not the same areas, he said.
The areas which 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.
Raichle was at the news conference to discuss his own work, on emotion and memory. He used the same type of functional MRI brain scans to examine 18 people who were asked to count the number of people in photographs.
Some of the pictures were neutral - the focus was things like furniture. Others were designed to create very negative emotions, such as pictures of mutilated bodies.
People were slower and less accurate when looking at the negative pictures and parts of the brain associated with emotion became more active, while parts associated with thought grew less so, he said.
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