Lovers, or would-be lovers, take note: Affairs of the heart can produce some pretty strong physical reactions.
There's more than a little bit of science about what goes on in a body -- and brain -- in love.
One study found that intense, passionate feelings of love activate reward systems in the brain that influence pain and reactions to addictive drugs.
Researchers at Stanford University and the State University of New York at Stony Brook did a brain-imaging study of 15 Stanford undergraduates who were in the first nine months of a romantic relationship to see what regions responded when they saw a photo of their significant other while experiencing pain.
When they looked at photos of their beloved and were put in mild pain by a heated device placed in the palm of their hand, the pain was reduced and imaging showed the love-induced pain relief came from regions associated with reward centers.
So romance may indeed be like an addiction, at least early on.
Being shown photos of an acquaintance didn't have the same effect, but being distracted with something like a word-association task (think of sports that don't involve balls) also lowered pain levels, but through a completely different brain pathway using higher, cortical parts of the brain, while the love connections used more primitive parts of the brain.
If affection can stop pain, rejection also exacts a toll.
Stress hormones shoot up after a breakup. Parts of the brain tied to emotion and pain, such as the anterior cingulate cortex, may contribute to aches, stress makes your stomach queasy and the heart skips a beat. Actually, the heart rate temporarily drops.
One Dutch study that set up college volunteers for (fake) acceptance or rejection by fictitious students at another university, found that heart rates dropped while awaiting an opinion, and fell even more and stayed that way longer if they were told the other student didn't like them.
The researchers said the results show that the autonomic, or involuntary, nervous system that regulate the heart and digestive system, fires up when a person is socially rejected.
Marriage also seems to offer the heart some protection. Married men and women have a significantly reduced chance (about 60 percent less) of dying from a heart attack than their unmarried counterparts, the European Journal of Preventive Cardiology reported last month.
Researchers at Finland's Turku University Hospital studied data on more than 15,000 people who suffered heart attacks between 1993 and 2002, half of whom died within 28 days. Researchers said that, although reasons behind different survival rates are unclear, married people generally are healthier, are more likely to follow medical advice and have more social support.
Back in the brain, research also shows that oxytocin, the hormone that's key to bonding between romantic partners and between mothers and their children, can help keep men from straying.
German researchers found that men in committed relationships, when given a boost of oxytocin, will keep more distance from an unknown woman they find attractive.
Healthy males were given a nasal spray containing either the hormone or a placebo, and 45 minutes later were introduced to a female subject they later described as "attractive." As the woman moved toward or away from each man, he was instructed to indicate whether she was at an "ideal distance" and when she moved to a distance that made them feel uncomfortable.
Men who were in a relationship and were given oxytocin kept a greater distance (at least four to six inches) when they approached or were approached by the woman. The hormone made no difference to the reactions of single men.
Earlier research with the hormone in prairie voles has showed that oxytocin was key in keeping the animals monogamous - they generally mate for life. The hormone is also known to increase levels of trust, which could have prompted all the men to allow the attractive female to come closer.
In a recent experiment, voles that got steady doses of oxytocin for several weeks rather than in short bursts showed that males became indifferent to their mates. Vole moms stopped doting on their pups.
No one's tried this test on people yet, but the results may make another point: Sometime too much cuddling, artificial or not, may not be good for a relationship over the long run.