JOIN USA new research using brain scans suggests some married couples hold on to that passion and romance for decades or more.
While gazing at a photo of their beloved, the brains of couples married 10 or more years who considered themselves "intensely" in love with their partners, lit up similarly to scans of newly in-love couples.
Scientists studied couples who considered themselves "intensely" in love.
The 17 study participants weren't just happily married, said study co-author Arthur Aron, a professor of psychology at Stony Brook University in New York. These were spouses who couldn't keep their hands off each other even though they'd been married for more than 21 years, on average.
"They told us things like, 'We drive our friends crazy. We're physically all over each other,'" Aron said.
"We're talking about people who have this intense connection, huge amounts of physical liveliness and passion. This is the sort of thing people thought was impossible or crazy. Our data suggest it's real."
The study was published online recently in the journal Social Cognitive and Affective Neuroscience.
Study participants had answered an ad that asked: "Are you still madly in love with your long-term partner?" The researchers screened them using several questionnaires that asked about their sexual frequency (an average of 2.2 times a week) and to what degree their spouse was the most important person in their life and how their body responds when they're close to their spouse.
The 10 women and seven men then underwent functional MRI while looking at a series of photos that included the object of their affection; a close, long-term friend; a long-term acquaintance; and a shorter-term acquaintance.
Brain scans showed the ventral tegmental area and dorsal striatum lit up when participants looked at their spouse's photo.
Prior studies have shown those dopamine-rich regions of the brain, which are associated with reward and motivation, also light up in couples when they first fall in love, as well as when people snort cocaine.
"These people are not just kidding themselves. They seem to be having the same experience as newly in-love people," Aron said.
Long-term, madly in love participants also showed more activation in regions of the brain associated with maternal attachment and pair-bonding, Aron said.
Sexual frequency was associated with increased activity of the posterior hippocampus, an area implicated in hunger and craving.
Yet long-term marrieds differed in at least one substantial way from the newly married. Areas of the brain associated with obsession and anxiety lit up less than in scans of new couples. Instead, brain areas associated with calmness were more active, Aron said.
But, skeptics say it was a small study that measured couples at a single point in time. They say couples can go through phases.
Happiness tends to dip when couples have children. As the children leave the house some couples have a relationship rebirth.
So this study might really be showing that it's possible to fall in love again than maintain that new love for years and years.
Robert Epstein, a research psychologist in San Diego, Calif, who specialises in love and relationships, expressed some skepticism about the findings.
"The study involved only a small number of participants, and researchers may have overreached in their conclusions," he said.
Because participants were measured at a single point in time, the study may suggest that it's possible to fall in love again, rather than show it's possible to maintain that "new love" for years and years.