It may be better to have loved and lost than never to have loved at all, but why is it so hard to find again? It may be that our brains are fixated on our former lovers, according to scientists. 

    Researchers at Florida State University examined the nature of love by studying the brains and behaviour of male prairie voles, picked for their habit of lifelong monogamy and aggression towards other females once they have found a mate. 

    The scientists found that males became devoted to females only after they had mated. The bond coincided with a huge release of the feelgood chemical dopamine inside their brains. 

    Brandon Aragona, who led the study, demonstrated that dopamine was the voles' love drug by injecting the chemical into the brains of males who had not yet had sex with female companions. Immediately, they lost interest in other females and spent all of their time with their chosen one. Further experiments showed that dopamine restructured a part of the vole's brain called the nucleus accumbens, a region that many animals have, including humans. The change was so drastic that when paired-up males were introduced to new females, although their brains still produced dopamine on sight, the chemical was channelled into a different neural circuit that made them go cold towards the new female. 

    "It seems that the first time they get together and the bond forms, it locks them into that monogamous behaviour ... You can take a female away from a male once he's formed a bond with her and two weeks later put him with a different female and he won't be remotely interested," said Dr Aragona, whose study appears in the journal Nature Neuroscience. 

    The researchers said that while the love lives of voles differ from those of humans, the same brain structures work in much the same ways across different species. "Things are always going to be more complicated in humans because we have larger brains and are under different pressures, but the basic mechanisms are there", said Dr Aragona. 

    或許愛過以后再失去也比根本不再去愛強，但為什么許多人在失戀后卻很難再愛一次？科學家最新的研究結果表明，這可能是人的大腦被一種叫做多巴胺的“癡情毒藥”鎖定在舊情人的身上。 

    據《衛報 》12月6日報道，美國佛羅里達州大學的研究人員通過研究雄性田鼠的大腦和行為來探索人類愛情的本質。和人一樣，田鼠屬于終生單配偶動物（即一夫一妻制），且一旦有了配偶后就本能地對其它異性產生排斥。 

    研究人員發現，雄性田鼠有了配偶后就會專注于對方，而有了配偶的田鼠開始大量分泌一種叫做多巴胺的化學物質（人腦也會分泌該物質）。負責此項研究的布蘭登·阿拉戈納博士證實，多巴胺就是讓雄性田鼠癡情的“毒藥”。 

    當尚未與雌鼠發生性關系的雄鼠的大腦被注入多巴胺后，這些雄鼠很快就失去了對其它異性的興趣，而只是專注于自己心儀的雌鼠上。進一步實驗表明，多巴胺改變了田鼠大腦中核團區域（大腦核團區域的功能是維持情緒和目的性行為，人也有）的結構。當已有配偶的雄鼠被介紹給新的雌鼠時，盡管此時雄鼠的腦中還在繼續分泌多巴胺，但多巴胺會被導入另一個完全不同的神經中樞系統，使得雄鼠對新的雌鼠毫無興趣。 

    阿拉戈納博士指出：“研究發現，雄鼠與雌鼠一旦結合在一起，它們就成為了單配偶動物。若將雄鼠與配偶分開，兩周后再讓它與新的雌鼠接觸，你會發現它對新的對象根本提不起興趣。”

    研究人員指出，盡管人的情感與田鼠的還有很大差別，但在不同的物種之間，相同的大腦結構也會有相似的運作方式。阿拉戈納博士說：“人類的情感會更加復雜，因為人腦體積更大且所處的環境也更復雜，但人腦與田鼠大腦基本的運作方式是相同的。”