你天生享受运动乐趣吗?
It’s possible that some of us are born not to run. According to an eye-opening new genetics study of lab rats, published in The Journal of Physiology, the motivation to exercise — or not — may be at least partly inherited.
很可能，我们中的一些人不擅长跑步纯属“自然灾害”。最近在《生理学杂志》(The Journal of Physiology)上发表的一项研究令人大开眼界：这项在实验室大鼠身上进行的新型遗传学研究表明，锻炼(或不锻炼)的动机至少有一部分是由遗传决定的。
For years, scientists have been bedeviled by the question of why so few people regularly exercise when we know that we should. There are obvious reasons, including poor health and jammed schedules. But researchers have begun to speculate that genetics might also play a role, as some recent experiments suggest. In one, published last year, sets of fraternal and identical adult twins wore activity monitors to track their movements. The results indicated that the twins were more alike in their exercise habits than a shared upbringing alone would explain. Their willingness to work out or sit all day depended to a large extent on genetics, the researchers concluded.
多年来，有个问题一直困扰着科学家们：为什么人人都知道应该经常锻炼，但真正能做到的却寥寥无几?有一些原因显而易见，譬如健康状况不佳，以及忙得抽不出时间来等。但是，最近的一些实验结果促使研究人员猜测遗传是否也在其中发挥了一定的作用。一项发表于去年的实验招募了若干组异卵和同卵双生的成年双胞胎，并要求他们佩戴活动监视器以跟踪行踪。结果表明，这些双胞胎运动习惯间的相似性远非仅凭生长在同一个环境所能解释。研究人员得出了这样的结论：他们是愿意去锻炼还是想一整天都坐着不动，在很大程度上取决于遗传。
But which genes might be involved and how any differences in the activity of those genes might play out inside the body were mysteries. So scientists at the University of Missouri recently decided to delve into those issues by creating their own avid- or anti-exercising animals.
然而，究竟有哪些基因参与其中，它们的活性差异又是如何在体内发挥作用的，这些都仍是未解之谜。因此，最近，密苏里大学(University of Missouri)的科学家们决定自己培养出喜欢和讨厌运动的动物品系，进而对上述问题进行深入探讨。
They accomplished this task by inter-breeding normal rats that had voluntarily run on wheels in the lab. The male rats that had run the most were bred with the female rats that also had run the most; those that had run the least were likewise mated. This scheme continued through many generations, until the scientists had two distinct groups of rats, some of which would willingly spend hours on running wheels, while the others would skitter on them only briefly, if at all.
为了达成这个目标，他们根据正常实验室大鼠自愿在跑轮上跑动的情况，对其进行了杂交——让最喜欢跑动的雄性大鼠与最喜欢跑动的雌性大鼠交配;同理，让最讨厌跑动的雄性大鼠与最讨厌跑动的雌性大鼠交配。这一方案持续进行了许多世代，直至科学家们获得了两组截然不同的大鼠品系：其中一组可以一连在跑轮上跑数个小时也乐此不疲，而另一组大鼠就算上了跑轮也只是漫不经心地从上面一窜而过——这还是在它们肯赏光动一动的情况下。
In their first experiments with these rats, the researchers found some intriguing differences in the activity of certain genes in their brains. In normal circumstances, these genes create proteins that tell young cells to grow up and join the working world. But if the genes don’t function normally, the cells don’t receive the necessary chemical messages and remain in a prolonged, feckless cellular adolescence. Such immature cells cannot join the neural network and don’t contribute to healthy brain function.
在关于这些大鼠的第一项实验中，研究人员发现它们脑部某些特定基因的活性存在着一些有趣的差异。在正常情况下，这些基因会制造一些蛋白质，指导幼稚细胞生长发育，好尽快加入具有工作能力的成熟细胞的行列。但如果这些基因不能正常发挥其功能，细胞接受不到必要的化学信息，就只能长期滞留在无功能的“细胞青春期”。这类未成熟细胞无法联入神经网络，因此就不能为健康的大脑功能作出应有的贡献。
In general, these genes worked normally in the brains of the rats bred to run. But their expression was quite different in the non-runners’ brains, particularly in a portion of the brain called the nucleus accumbens, which is involved in reward processing. In humans and many animals, the nucleus accumbens lights up when we engage in activities that we enjoy and seek out.
一般而言，在科学家们培养出的“跑步爱好者”大鼠的脑部，这些基因可以正常发挥功能。但在那些“非跑步爱好者”大鼠的脑部，这些基因的表达情况截然不同，在名为“伏隔核”的脑区中尤其明显。伏隔核与奖励加工有关，当人类和许多动物从事自己喜欢或渴求的活动时，伏隔核就会处于激活状态。
Presumably as a result, when the scientists closely examined the brains of the two types of rats, they found that by young adulthood the animals bred to run had more mature neurons in the nucleus accumbus than did the non-runners, even if neither group had actually done much running. In practical terms, that finding would seem to indicate that the brains of pups born to the running line are innately primed to find running rewarding; all those mature neurons in the reward center of the brain could be expected to fire robustly in response to exercise.
或许正是因为这个原因，在科学家们仔细检查了这两组大鼠的脑部后，他们发现：同样是处于年轻成年期，“跑步爱好者”大鼠伏隔核中的成熟神经元要多于 “非跑步爱好者”大鼠，即使在两组大鼠实际上都未进行过大量跑动时依然如此。从实际角度而言，这一研究结果表明，“跑步爱好者”大鼠品系的幼崽在头脑里天生就觉得奔跑是一大快事;可以想见，在运动的刺激下，它们脑部奖励中心的所有成熟神经元都将强烈地兴奋起来。
Conversely, the rats from the reluctant-running line, with their skimpier complement of mature neurons, would presumably have a weaker innate motivation to move.
相反，在“非跑步爱好者”大鼠品系中，成熟神经元“供应不足”，因此它们参加运动的先天性动机可能就比较弱。
Those results would be disheartening, except that in the final portion of the experiment the scientists had reluctant runners exercise by setting them on running wheels, while also providing some born-to-run animals with wheels. After six days, the unwilling runners had accumulated far less mileage, about 3.5 kilometers (two miles) per rat, compared to almost 34 kilometers each by the enthusiasts.
乍一看来，这些研究结果颇令人沮丧，但实验的最后部分重又燃起了人们的希望。在这一阶段的实验中，科学家们把“跑步爱好者”大鼠与“非跑步爱好者” 大鼠一起放在跑轮上，这样，当前者欢快地奔跑时，后者也被迫要跟着走几步。六天后，它们的累积奔跑里程约为平均每只大鼠3.5千米(两英里)，远远少于 “跑步爱好者”大鼠(平均每只大鼠近34千米)。
But the halfhearted runners’ brains were changing. Compared to others in their family line that had remained sedentary, they now showed more mature neurons in their nucleus accumbens. That part of their brain remained less well developed than among the naturally avid rat runners, but they were responding to exercise in ways that would seem likely to make it more rewarding.
然而，在这些三心二意的跑步者的脑部，改变正在悄然发生。研究显示，现在它们伏隔核中的成熟神经元数量已经超过了同一品系中依然保持久坐不动生活习惯的同伴们。虽然就该脑区的发育程度而言，它们仍然不能与那些天生的跑步爱好者们相提并论，但它们脑部对运动的应答方式很可能已经开始促进它们更加乐于运动。
What, if anything, these findings mean for people is “impossible to know at this point,” said Frank Booth, a professor of biomedical sciences at the University of Missouri who oversaw the study. Rat brains are not human brains, and rat motivations are at best opaque.
这些研究结果对人类意味着什么——是说，如果它们的确具有一定意义的话——“尚未可知，”该研究的负责人，密苏里大学的生物医学教授弗兰克·布思(Frank Booth)说。大鼠的脑并不能等同于人类的脑，况且，现在人们对于大鼠的动机充其量也只是一知半解的状态。
Even so, Dr. Booth said, his group’s data would seem to suggest “that humans may have genes for motivation to exercise and other genes for motivation to sit on the couch,” and over generations, one set of these genes could begin to predominate within a family. But predispositions are never dictatorial.
即便如此，布思博士指出，他团队的研究数据表明：“在人类体内，很可能也存在激励运动的基因，以及让人赖在沙发上充当‘沙发土豆’的其他基因。”经历数代之后，其中一组基因或许会开始在某一家族内占据主导地位。但是，先天性倾向从来都不会是唯一的决定因素。
“People can decide to exercise,” whatever their inheritance, Dr. Booth said, and, as his study’s final experiment suggests, they could rewire their brains so that moving becomes a pleasure.
无论遗传背景如何，“人们都一样可以选择去做运动，”布思博士说，正如他研究中最后的实验所显示的，人们可以重整脑部的神经连接，让运动成为一种乐趣。