为什么总想吃甜食？原来是大脑在作怪

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Why our brains are programmed to eat doughnuts

Last updated at 11:20am on 10th March 2008



Scientists have discovered that it is not just Homer Simpson who finds it impossible to keep his hands off doughnuts.

Apparently our brains are programmed to leap into action when presented with the sugary treats.

A study found that when hungry volunteers were shown a picture of a Krispy Kreme doughnut or a screwdriver, the sugary snack sent the brain into overdrive.

The same response did not occur after participants had stuffed themselves with up to eight of them.

Researchers at Northwestern University in Chicago carried out functional magnetic resonance imaging (fMRI) brain scans while volunteers were shown the pictures.

After the eating binge, neither image generated much of a reaction.

But after volunteers had fasted for eight hours, two distinct parts of the brain \"lit up\" at the sight of the doughnuts.

The first was the limbic brain, an ancestral part of the brain present in all animals from frogs to humans.

\"That part of the brain is able to detect what is motivationally significant,\" said Dr Marsel Mes***, senior author of the research published on line in the journal Cerebral Cortex.

\"It says, not only am I hungry, but here is food.\"

Next the brain's spatial attention network locked onto the doughnuts, deciding they were more important than the screwdrivers.

Dr Aprajita Mohanty, another of the scientists, said: \"There's a very complex system in the brain that helps to direct our attention to items in the environment that are relevant to our needs, for example, food when we are hungry but not when we are full.\"

The research demonstrated how the brain sifts out all sorts of relevant material, not just doughnuts, from a world full of stimuli.

\"If you are in a forest and you hear rustling, the context urges you to pay full attention since this could be a sign of danger,\" said Dr Mes***.

\"If you are in your office, the context makes the identical sound less relevant. A major job of the brain is to match response to context.\"

科学家发现，并不仅仅是霍默-辛普森发现让他的双手远离甜甜圈是不可能的。很明显，当呈上甜味品时，我们的大脑会机械地采取行动。
一项研究发现，当向饥饿的志愿者展示KK甜甜圈和螺丝钻鸡尾酒的图片时，甜甜圈刺激大脑高速运转。但当参与者以8个甜甜圈填饱肚子后，没有观察到相同的反应。在向志愿者展示图片时，芝加哥西北大学的研究者进行了fMRI（功能性磁共振成像）大脑扫描。一顿暴食后，没有一张图像能产生那么多反应。
当志愿者禁食8h后，大脑的两个不同部分一看见甜甜圈便发亮。首先是边缘脑，大脑的一个古老部位，存在于从青蛙到人的所有动物中。 “大脑的另一部位能够检测什么刺激是重要的，它不仅告诉我饿，而且告诉食品在这里。”发表在〈大脑学杂志〉上的该研究的第一作者Mesu lam博士如是说。接着，大脑的空间注意网络锁定在甜甜圈上，认为他们比螺丝钻鸡尾酒更重要。
另一个科学家Mohanty博士说，“大脑内有一个复杂的系统以帮助我们将注意力集中在环境中与我们需求相关的东西上，例如，当我们饥饿时需要食物，而吃饱了则不需要。”该研究论证了大脑如何从充满刺激的外界中筛选出各种相关的东东，而不仅仅是甜甜圈。
Mesu lam博士说，“如果你在森林里听到沙沙声，背景将促使你集中精力，因为这可能是一个危险信号。但如果你在办公室，背景则将同样的声音视为关系不大。大脑的主要工作是让反应与背景相匹配。”