Human brains are slow to develop--a secret, perhaps, of our success

人腦發(fā)育緩慢——或許是人類成功的奧秘

By Melody Dye  | February 9, 2010 | 

At every stage of early development, human babies lag behind infants from other species.  A kitten can amble across a room within moments of birth and catch its first mouse within weeks, while its wide-eyed human counterpart takes months to make her first step, and years to learn even simple tasks, such as how to tie a shoelace or skip a rope, let alone prepare a three-course meal. Yet, in the cognitive race, human babies turn out to be much like the tortoise in Aesop’s fable: emerging triumphant after a slow and steady climb to the finish. As adults, we drive fancy sports cars, leap nimbly across football fields and ballet stages, write lengthy dissertations on every conceivable subject, and launch rockets into space.  We have a mastery over our selves and our environments that is peculiar to our species.

在早期發(fā)育的每個階段，在發(fā)育速度上，人類的嬰兒都被其他動物的幼崽甩在了后面。小貓崽降生不久就能橫穿房間漫步，幾周內(nèi)就能抓到第一只老鼠；而它們天真的對手——人類的嬰兒卻要花幾個月才能邁出第一步，幾年才能學(xué)會簡單的任務(wù)，諸如如何系鞋帶、跳繩或者獨(dú)自準(zhǔn)備有三道菜的一餐飯。在認(rèn)知能力的競賽中，人類更是慢得像伊索寓言里的烏龜：經(jīng)歷緩慢而沉穩(wěn)的爬行才到達(dá)終點(diǎn)。作為成年人，我們能操縱設(shè)計精妙的跑車；無論在足球場上還是在芭蕾舞臺上，我們都能敏捷矯健地跳躍自如；在任何能想像到的領(lǐng)域，我們都能寫出長篇大論的論文；我們甚至還能把火箭送上太空。

Yet, this victory seems puzzling. In the fable, the tortoise wins the race because the hare takes a nap. But, if anything, human infants nap even more than kittens! And unlike the noble tortoise, babies are helpless, and more to the point, hopeless. They could not learn the basic skills necessary to their independent survival even if they tried. How do human babies manage to turn things around in the end?

是的，勝利來得很蹊蹺。在寓言里，烏龜獲勝是因?yàn)橥米哟蛄隧?。如果是因?yàn)檫@個的話，那人類嬰兒打得盹可比小貓崽還要多！而且，與高貴的烏龜不同，人類的嬰兒很無能，更糟的是，他們簡直不可救藥。無論怎么嘗試，他們也無法獨(dú)自學(xué)會生存所需的基本技能。那么人類的嬰兒最終是如何扭轉(zhuǎn)局勢的呢？

In a recent article in Current Directions in Psychological Science, Sharon Thompson-Schill, Michael Ramscar and Evangelia Chrysikou make the case that this very helplessness is what allows human babies to advance far beyond other animals. They propose that our delayed cortical development is precisely what enables us to acquire the cultural building blocks, such as language, that make up the foundations of human achievement. Indeed, the trio makes clear that our early vulnerability is an evolutionary “engineering trade-off,” much like the human larynx—which, while it facilitates the intricate productions of human speech, is actually quite a precarious adaptation for anyone trying to swallow safely. In the same way, they suggest, our ability to learn language comes at the price of an extended period of cognitive immaturity. 

在《心理學(xué)》雜志的“潮流方向”欄目中，由Sharon Thompson-Schill、 Michael Ramscar 和 Evangelia Chrysikou三人發(fā)表了一篇文章。文中闡述了正是由于人類嬰兒的無能，使得他們與其他動物相比占了巨大優(yōu)勢。文章認(rèn)為，人類延后的腦皮質(zhì)發(fā)育恰恰使得人類獲得了構(gòu)筑文化的基石，例如語言，構(gòu)成了人類成功的基礎(chǔ)。文章明確了人類早期的弱點(diǎn)是進(jìn)化的“工程協(xié)議”，就像人的喉嚨一樣，當(dāng)它能夠發(fā)出復(fù)雜的人類語言時，同時也使安全的吞咽有了相當(dāng)?shù)牟淮_定性。同樣地，文章還指出，人類學(xué)習(xí)語言的能力是以長時期的認(rèn)知不成熟為代價的。

This claim hinges on a peculiar and unique feature of our cognitive architecture: the stunningly slow development of the prefrontal cortex (PFC). While other animals’ brain regions development in synchrony, in humans, the development of the PFC lags far behind that of other areas. The PFC is the swath of gray matter that makes up the anterior frontal lobes, and functionally, it appears to be heavily implicated in a wide-range of sophisticated planning and attention driven behaviors. Indeed, it is often referred to as the “control” center of the brain. One of its main functions appears to be that of selectively filtering information from the senses, allowing us to attend to specific actions, goals, or tasks. For this reason, “cognitive control” tasks are thought to be one of the best assessors of PFC function and maturity, and they are tests that young children reliably, and ignominiously, fail.

這一觀點(diǎn)是基于人類奇特而獨(dú)一無二的認(rèn)知結(jié)構(gòu)——發(fā)育驚人緩慢的前額皮質(zhì)（PFC）。其他動物的大腦區(qū)域發(fā)育是同步的，而人類的PFC發(fā)育遠(yuǎn)遠(yuǎn)慢于大腦其他區(qū)域。PFC是組成額葉前部的一排灰質(zhì)，在功能上，它與廣泛的復(fù)雜規(guī)劃和注意力導(dǎo)向行為密切相關(guān)。的確，它通常被認(rèn)為是大腦的“控制”中心。它的一個主要功能是有選擇性地過濾外部信息，使得我們專注于特定的行為、目標(biāo)或任務(wù)。因此，能否“有認(rèn)知地操控”任務(wù)被認(rèn)為是評價PFC的功能和成熟度的最佳標(biāo)準(zhǔn)，而確定和遺憾的是，這項標(biāo)準(zhǔn)小孩子顯然無法通過。

The Stroop task serves as a simple assessor of PFC function in adults. The task involves naming the ink color of a contrasting color word: for example, you might see the word “red” written in green ink, in which case you have to say “green.” The task is tricky since it demands that we override a well learned response (saying “red” in response to seeing the word red) with a new response specific to the task (naming the conflicting ink color). Tricky or not, healthy adults can successfully complete the task with only minor hesitation.

對成年人來說，PFC功能最簡單的評價標(biāo)準(zhǔn)是斯特魯法（Stroop task）。測試包括說出墨水的顏色，而這墨水寫出的字代表著另一種顏色。比如，你可能會看到用綠墨水寫的“紅”字，而你應(yīng)該說出的是“綠”。這個測試很棘手，因?yàn)樗笪覀冝饤壋Ｒ?guī)反應(yīng)（說出“紅”是我們看到紅這個字的常規(guī)反應(yīng)），而去做出一個針對該測試的新的反應(yīng)（說出墨水顏色）。無論棘手與否，健康成年人都能成功通過，只需要稍稍遲疑。

Children, with their immature PFC’s, are a different story. Typically, the younger children are, the worse they are at solving Stroop-like tasks, and under the age of four, they outright fail them. While young children are sensitive, apt learners, and often appear to fully understand what is being asked of them, they are unable to mediate the conflicting demands present in these sorts of tasks, and thus fail them, time and time again. Three-year olds simply cannot direct how they attend to or respond to the world.

由于PFC不成熟，對于該測試，兒童的情況就不一樣了。一般地，兒童年齡越小，在斯特魯測試中的表現(xiàn)越糟。4歲以下的兒童則完全無法通過測試。盡管小孩子敏感、樂于學(xué)習(xí)并常?？此仆耆靼啄愕膯栐?，他們卻無法解決在這類測試中所展現(xiàn)的矛盾的需求，因此一次又一次地測試失敗。3歲大的兒童一般無法對自身目的和對外界的反應(yīng)做出明確指向。