Love, said Shakespeare, is “an ever-fixed mark / That looks on tempests and is never shaken”. On the contrary, wrote Swinburne, “Laurel is green for a season, and love is sweet for a day; / But love grows bitter with treason, and laurel outlives not May”. And so on . . . with infinite variations. Love is (or should be) the core of human experience, triggering every emotion from euphoria to despair as we write about it, sing about it, hope for it, worry about it and cry about its irrationality and transience. But the examination of love is no longer confined to the imagination. Where poets once conjured metaphors, scientists now probe the mental circuits that deliver its wild emotions. Love has no secrets from neurologists armed with an MRI brain scanner. What they have found contradicts the cynics: there is such a thing as everlasting love.

Researchers at Stony Brook University in New York have shown that the traditionally sorry path of sexual love - a downward spiral from lust to indifference over the space of a decade - is not an iron rule. Scanning the brains of people who have been together for 20 years, the scientists found that about one in 10 couples still display elements of “limerence”, the psychologists’ term for the obsessive behaviour of new lovers. They enjoy “intensive companionship and sexual liveliness” but without the anxieties and tensions of early love. They are generous, calm and deeply attached. The scientists call them swans (swans mate for life). This is good news for the 10%, if not for the remaining 90% gripped by marital fatigue. But Arthur Aron, leader of the researchers, says the majority can learn from the minority. One clue he has found is that the swans share experiences and avoid stress. This may be a symptom rather than a cause, but Aron, 64, and his wife are copying the swans anyway in the hope of enjoying a little limerence themselves.

If we cannot all be swans, the other good news is that Aron’s team has established a biological basis for romance. Science has long dismissed the idea of love as “culturally determined”, existing only in societies that believe in it. But Aron and co have found identical brain patterns in lovers from New York to Beijing. Unromantically, they say love is born in the brain’s reward-seeking circuitry, not the heart, but we are no worse off for that. Love matters. It is not confined to Christmas repeats of Love Actually and other daft (but really not so wide of the mark) Richard Curtis films. The absence of love from generation to generation led to the death of Baby P and other outbreaks of depravity that scarred 2008. As we face the tempests of 2009, love must remain the “ever-fixed mark” that is never shaken.