"I feel your pain," the politician assures constituents who have just lost jobs.

"This hurts me as much as it does you," the doctor tells a child.

Maybe it's true, according to the latest discovery in a rapidly growing field of research sometimes termed "social neuroscience."

Researchers reported in the journal Science yesterday that the brain circuits for processing pain turn on when someone sees a loved-one suffering. They produce some of the same sensations that would occur if the witness were actually being hurt.

"For real life, it means that we care much more about other people than perhaps generally assumed," said Dr. Tania Singer, the lead researcher. "Whether we act accordingly, in a helpful way, is another question. Probably we are very good in controlling empathy."

Singer and her associates at University College London did the study to probe empathy -- the ability to understand the feelings, thoughts, beliefs, and intentions of other people -- one of the traits said to define human nature. Empathy probably helped early humans survive by driving them to help each other.

Philosophers once argued that empathy was a moral value that people had to learn, but a tool called functional magnetic resonance imaging shows that empathy is hard-wired into the human brain.

Regular MRI machines in hospitals show how the brain looks. The fMRI scans show how it works as thoughts, sensations and emotions occur over time. By taking fMRI images while people think and do different tasks, scientists have identified brain activity involved in love, trust, a sense of justice, and other feelings.

Dr. Helen Mayberg, a neuropsychiatrist at Emory University in Atlanta, described the new fMRI study as "brilliant" in revealing empathy's roots deep inside the brain.

It involved 16 romantically involved couples, who were thought to be very sensitive to each others' feelings. Researchers watched each woman's brain with fMRI while delivering an electric shock either to her hand or to her partner's hand. The women could not see their partner's faces, but an indicator told them who would get the shock and how strong it would be.

When the women got shocks, pain regions in their brains lit up. Some of the same areas lit when the indicator showed their partners being shocked.

Physical pain activated brain regions involved in processing information for particular parts of the body. Empathy activated only those regions that trigger a sense of suffering.

Researchers focused on empathy in women only because this was their first study and they wanted to limit it to one sex, Singer said. Men, she added, probably respond in the same way as women, although other research hints that they are "slightly less empathic in general."