Why The Brain Has So Many Folds


  "Dear A Moment of Science, I know the human brain is an incredible thing, the most complex object in the known universe. But, honestly, it’s not much to look at. Just a big, gray, foldy lump. And what’s with all those folds? Why does the brain look a lot like a scrunched up piece of paper?"


  Our brains, and the brains of some other animals, have a lot more in common with a balled up piece of paper than you might think.


  First, though, it’s worth mentioning that not all brains look the same. Some animals, including rats and mice, have smooth brains. No folds or wrinkles. Humans and other animals, such as pigs, have brains with many folds.


  Scientists at the University of Rio de Janeiro have been trying to figure out what accounts for the folds. One idea postulated that as brains evolve and the more neurons they have, the more folds are required to allow neurons to form connections. But elephants have nearly twice as many folds in their brains yet have fewer neurons than we do, so that theory seems improbable.


  The researchers have, however, determined that how human brains fold follows the same physical principles guiding folds and creases resulting from crumpling a sheet of paper. That’s interesting because it enabled the scientists to reason that the two main factors determining a brain’s shape are the surface area and thickness of the outer layer cortex. The larger the cortex surface area, the more folds a brain will have. But greater thickness results in fewer folds.


  Same goes for a piece of paper.

  


  ps: 一项新的研究显示,我们的大脑之所以布满褶皱并具有核桃似的形状,是因为大脑皮层即灰质的快速生长受到了白质的限制。研究人员发现,大脑皮层凹陷的沟和隆起的回取决于两个简单的几何参数———灰质的生长速度及其厚度。发表在美国《国家科学院学报》月刊上的研究显示,可以在实验室利用双层凝胶模拟大脑褶皱的形成。研究人员指出,除了这些限制,基因也对决定大脑形状有所影响,因为基因对神经细胞如何增殖并移动到它们的目的地起调控作用。所有哺乳类物种都有大脑皮层,但只有较大型的哺乳类才具有褶皱的大脑皮层。举例而言,老鼠大脑的表面光滑,而比这大得多的大脑,比如人类的大脑则具有大量沟回。褶皱的大脑皮层拥有更大的表面面积,这就意味着具备更强大的信息处理能力,但尚未完全清楚是什么因素决定了人类大脑的标志性沟回形状。


    掌握大脑是如何形成褶皱的,可能有助于科学家更好地解释多小脑回、巨脑回、无脑回等先天性病症。历史上,关于脑沟和脑回是如何形成的有三种思路:一种看法是,大脑皮层的某些区域生长较快进而比其他区域凸出,形成了脑回。另一个看法是,相互之间高度关联的神经细胞群被构成白质的丝状轴突机械地拉近距离。然而,证据表明上述两种观点都不正确。第三种看法是,灰质的生长超过白质,形成了“褶皱“,令大脑皮层具备这种形状。但研究人员称,模拟这种褶皱的早期尝试并未获得成功。在此前的研究中,研究人员假设灰质是薄且坚硬的,在厚且柔软的白质上生长,但根据这种假设所产生的褶皱与真实的人类大脑上的褶皱并不相同。在新的研究中,研究人员假设灰质和白质具有相似的坚硬程度,但生长速度不同。


    利用数学模拟的方法,根据大脑大小的不同,他们的模拟产生了不同的大脑皮层形状。举例而言,直径不足1.3厘米的小型大脑预计会产生光滑的大脑皮层。中等大小的大脑预计会在灰质中产生一些脑沟,而体积较大的大脑则会变得十分褶皱,会有脑沟陷入白质。科学家们还利用双层膨胀凝胶材料复制了大脑形成褶皱的现象,并表明,只有这两层具备相似的柔软程度时,形成的褶皱看上去才会与人类大脑的脑沟和脑回相似。研究人员指出,虽然他们的模拟可用于最基本的脑沟和脑回,但这并不能解释大脑更加复杂的特征,比如,将左右脑分开的大脑纵裂,以及区分大脑主要脑叶的其他大的脑沟。


  ——美国趣味科学网站

  论坛翻译地址:http://forum.putclub.com/forumdisplay.php?fid=113&page=1&filter=type&typeid=148&orderby=dateline



眼睛的发展简史


  A Brief History of Eyeglasses

  Spec-tacular Inventions


  When you think about inventions that have radically changed human existence, what comes to mind? Probably the wheel, the printing press, maybe the refrigerator and definitely personal computers. Then there are those more mundane things that we rarely think about, but without which we’d be much worse off. Like eyeglasses, for example. Imagine a world without glasses—many of us would walk around bumping into things and driving our cars up onto the sidewalk. So who invented glasses, and how were they first made?


  The truth is that nobody knows who invented eyeglasses. At some point in Italy between 1268 and 1289 someone came up with the idea, but the actual inventor remains anonymous. What we do know is that the earliest lenses were made from quartz and were usually set into bone, metal, or leather. As soon as early opticians figured out how to make glass without bubbles and other obstructions, they started making lenses out of glass.


  Ye Olde Nose Pinchers


  Although glasses spread quickly throughout Europe and Asia, there was one major problem: Keeping them on the wearer’s face. Early glasses acted a bit like pinchers, squeezed onto the bridge of the nose. Ouch! It took nearly 400 years before opticians figured out that rigid sidepieces resting on top of the ears might do the trick.


  No history of spectacles would be complete without some mention of Benjamin Franklin, who invented bifocals in the 1780s. Annoyed at having to constantly switch glasses whenever he wanted to read or take in the sights while traveling, Franklin had his reading glasses cut in half and fused with his distance glasses. Now that’s American ingenuity for you.


  came up with 提出,想出

  quartz 石英

  optician n. 眼镜商;光学仪器商;光学仪器制造者

  rigid adj. 严格的;僵硬的,死板的

  bifocal n. 双光眼镜;双重焦点透镜

  ingenuity n. 心灵手巧,独创性;精巧

  


  PS:现在已经习惯成自然:当你的视力下降,你的眼睛变差了,你会去你的视光师或眼科医生那里配一副眼镜。但过去可不是这样的:直到13世纪人们才真正使用助视器来改善他们的视力。


  一、眼镜的历史


  数千年前,玛雅,埃及,中国和希腊的伟大文明创造了惊人的成就。然而,当涉及到保持视力,即使是最伟大的学者也无能为力。那时,就像今天一样,随着年龄的增大眼睛通常也慢慢变差。伟大的罗马演说家西塞罗曾抱怨一件麻烦事就是不得不让仆人读文章给他听。尼禄皇帝需要通过一颗绿宝石来观看他钟爱的角斗。希腊哲学家托勒密(约公元150)了解了光折射的最初规律,但是直到1000多年以后阿拉伯数学家和天文学家阿尔哈曾才明确了形成清晰视觉的最基本的折射定律。


  二、修道士发明了最早的助视器


  最终,13世纪时意大利的修道士手工精心制作了第一个半成形的立式镜片。这种镜片就像放大镜。为制作镜片,修道士使用了一种石英叫绿宝石。几年之后-1267年-牛津圣芳济会的修道士罗杰培根提供了科学的证据说明用特殊形状的立式镜片可以将小字放大。


  三、穆拉诺:眼镜的诞生地


  至今仍在全世界享有盛誉的威尼斯穆拉诺的玻璃工厂有理由声称自己是眼镜的诞生地。13世纪,他们是唯一能够制造纯粹的软玻璃的工厂。不久以后第一份质量标准出炉。这些眼镜,称为阅读助视器, 有一个凸起的立式镜片,边框是用铁,牛角或木头制成的。那时只有一种简单的硕大的镜片。总之,第一副眼镜只能用作远视者阅读用的助视器。


  四、眼镜成为身份的象征


  直到200年以后至少在某种程度上可以代表第一副现代眼镜的镜框被制造出来了:铆钉样眼镜被耳挂式眼镜所代替。镜框是一片式的。当然只有少数富人能够买得起这些铁制或青铜制的眼镜。在西班牙,特别大的眼镜被认为是身份的象征。皮制的鼻梁架也开始使用以使助视器戴起来更加舒适。那时最大的问题实际上是固定。镜框经常会从鼻子上滑落,由于镜框很重,很多时候佩戴者觉得戴起来非常不舒服。18世纪,所谓的纽伦堡有框眼镜在市场上出现。人们给它起了一个不怎么讨人喜欢的名字“nose-crushers“-但它却成为了一种时尚,并且佩戴起来比较舒适,而在这之前被认为是不可能的。


  大约在18世纪末,配有单片眼镜的镜架成为新宠。德国和英国上流社会有品位的淑女和绅士都戴这种眼镜。法国人则更喜欢“pince-nez“眼镜。也是单片镜片的镜架,但不仅可以戴在鼻子上,也可以利用眼周的肌肉固定。法国版的优势在于当有其他人在一起时可以迅速取下,因为德国的西方邻居们觉得戴pince-nez被人看到还是会有点尴尬。


  五、现代的框架眼镜


  直到上世纪的前20年框架眼镜才变成现在的外观和解剖学上的完美设计。如今,眼镜有各种各样的形状和材料-选择可以随心所欲。框架眼镜已经成为全世界最重要的助视器并且成为受众人欢迎的时尚配件。



  ——《科技在线》




2019年09月18日

这是今年最好的演讲:你这一生其实只有9年,请好好虚度!
郁达夫:《故都的秋》

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