Scientists have discovered true love. Brain scans have proved that a small number of couples can respond with as much passion after 20 years as most people exhibit only in the first flush of love.

The findings overturn the conventional view that love and sexual desire peak at the start of a relationship and then decline as the years pass.

A team from Stony Brook University in New York scanned the brains of couples who had been together for 20 years and compared them with those of new lovers. They found that about one in 10 of the mature couples exhibited the same chemical reactions when shown photographs of their loved ones as people commonly do in the early stages of a relationship.

Previous research suggested that the first stages of romantic love, a rollercoaster ride of mood swings and obsessions that psychologists call limerence, start to fade within 15 months. After 10 years the chemical tide has ebbed away.

The scans of some of the long-term couples, however, revealed that elements of limerence mature, enabling them to enjoy what a new report calls “intensive companionship and sexual liveliness.”

The reactions of these long-term couples to pictures of their beloved were identified on MRI brain scans as a burst of pleasure-producing dopamine more commonly seen in couples who are gripped in the first flush of lust.

“The findings go against the traditional view of romance – that it drops off sharply in the first decade – but we are sure it’s real,” said Arthur Aron, a psychologist at Stony Brook.

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