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(huo)許(xu)愛(ai)過(guo)以(yi)後(hou)再(zai)失(shi)去(qu)也(ye)比(bi)根(gen)本(ben)不(bu)再(zai)去(qu)愛(ai)強(qiang)
，但(dan)為(wei)什(shen)麼(me)許(xu)多(duo)人(ren)在(zai)失(shi)戀(lian)後(hou)卻(que)很(hen)難(nan)再(zai)愛(ai)一(yi)次(ci)
？科(ke)學(xue)家(jia)最(zui)新(xin)的(de)研(yan)究(jiu)結(jie)果(guo)表(biao)明(ming)，這(zhe)可(ke)能(neng)是(shi)人(ren)的(de)大(da)腦(nao)被(bei)一(yi)種(zhong)叫(jiao)做(zuo)多(duo)巴(ba)胺(an)的(de)“癡情毒藥”鎖定在舊情人的身上。 

    據《衛報 》12月6日報道，美國佛羅裏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
，田鼠屬於終生單配偶動物（即一夫一妻製），且一旦有了配偶後就本能地對其它異性產生排斥。 

    研究人員發現，雄性田鼠有了配偶後就會專注於對方，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dang尚shang未wei與yu雌ci鼠shu發fa生sheng性xing關guan係xi的de雄xiong鼠shu的de大da腦nao被bei注zhu入ru多duo巴ba胺an後hou

，這zhe些xie雄xiong鼠shu很hen快kuai就jiu失shi去qu了le對dui其qi它ta異yi性xing的de興xing趣qu，而er隻zhi是shi專zhuan注zhu於yu自zi己ji心xin儀yi的de雌ci鼠shu上shang。進jin一yi步bu實shi驗yan表biao明ming，多duo巴ba胺an改gai變bian了le田tian鼠shu大da腦nao中zhong核he團tuan區qu域yu（大腦核團區域的功能是維持情緒和目的性行為
，人也有）dejiegou。dangyiyoupeioudexiongshubeijieshaogeixindecishushi，jinguancishixiongshudenaozhonghaizaijixufenmiduobaan，danduobaanhuibeidaorulingyigewanquanbutongdeshenjingzhongshuxitong，shidexiongshuduixindecishuhaowuxingqu。 

    阿拉戈納博士指出：“研yan究jiu發fa現xian，雄xiong鼠shu與yu雌ci鼠shu一yi旦dan結jie合he在zai一yi起qi，它ta們men就jiu成cheng為wei了le單dan配pei偶ou動dong物wu。若ruo將jiang雄xiong鼠shu與yu配pei偶ou分fen開kai
，兩liang周zhou後hou再zai讓rang它ta與yu新xin的de雌ci鼠shu接jie觸chu

，你ni會hui發fa現xian它ta對dui新xin的de對dui象xiang根gen本ben提ti不bu起qi興xing趣qu。”

    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：“人類的情感會更加複雜
，因為人腦體積更大且所處的環境也更複雜，但人腦與田鼠大腦基本的運作方式是相同的。”