女人善多工 男人習慣專注
摘錄自：天下雜誌 經濟學人電子報 2013/12/20
2013-12-10 Web only 作者：經濟學人
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| 圖片來源：flickr.com/photos/76029035@N02/ |
大多數人都會同意，男人和女人的思考方式不同。科學也量化了部分差異；男人的動作和空間能力優於女性，思考模式比較專注於單一主題；女性記憶力較佳、更適應社會，同時處理多項事務的能力比較強。男女當然也有許多相似之處，但平均來看，前述的觀察是對的。
以演化觀點來解釋男女差異，是每個人都能玩的遊戲。最顯而易見的解釋就是，在狩獵採集時代，男人花比較多時間在營地之外漫遊，因此他們的腦部必須有能力找到回家的路；他們也花比較多時間在追蹤、戰鬥、獵殺動物及入侵者。相反地，女人則相互社交並照料小孩，因此她們必須有能力相互操控和控制小孩的情緒，才能在她們的世界中成功。
但從神經學觀點解釋性別差異，則完全是另一回事。想參加這場遊戲，得擁有昂貴的儀器才行；賓州大學的維瑪（Ragini Verma）團隊就擁有這樣的條件。他們標出了男女腦部連結的差異，並將這些差異與民間和心理學熱愛的刻板印象配在一起。
過去數十年間，各種掃描活腦的技術讓神經學得以出現了革命性進展。維瑪選擇的技術是擴散張量造影。這項技術可以追蹤腦部的水分子；由於連結神經細胞的纖維帶有脂肪鞘，其內部水份只能沿著纖維擴散，無法穿越脂肪鞘。因此，擴散張量造影才能偵測出這類纖維、看出它們通往何處。
人腦的兩大主要部分為負責思考的大腦，以及負責動作的小腦，兩者皆分為左右兩半。維瑪博士的團隊將此技術應用於428名男人和男孩，以及521名女人和女孩，結果發現，男人的大腦是以半腦內的連結為主，女人則是以兩個半腦之間的連結為主；小腦則剛好相反
此事代表的意義可以有各種解釋，但維瑪博士認為，連結差異是造成部分男女認知能力的不同的根源。左右大腦分別負責邏輯和直覺思考；在維瑪博士眼中，女人的兩個半腦會密集地相互溝通，這有助於解釋為何女性的記憶力、社會適應力和多工能力都比較好。相對地，男性半腦內的連結較密切，讓他們得以專注於不需要兩個半腦同時接受複雜資訊的事物，所以才會專注於單一主題。
至於小腦，男人的兩個半腦間擁有額外的相互連結，有助協調身體的動作。此事非常重要，因為兩個半腦分別控制一半的身體；因此，男人擁有比較強的動作能力，亦即協調性優於女人。
維瑪博士的另一項主要發現則是，多數差異並非先天，而是隨著年齡增加而發展。她的受測者年紀介於8至22歲；8至13歲的男孩和女孩身上只有少數差異，但都是隨後會變得十分明顯的差異。13至17歲的青少年的差異比較多，17歲以上的年輕成人則更多。因此，腦部的性別差異，要等到性別本身開始出現重要性的時候才會顯現──至少此技術看得到的那些差異是如此。
維瑪博士的研究不但結果重要，它還展現了擴散張量造影的能耐。研究腦部、特別是活腦，是個極為困難的科學問題；美國政府最近就承諾為此撥出大量金錢，推動名為「透過先進創新神經技術進行腦部研究」（Brain Research through Advancing
Innovative Neurotechnologies，BRAIN）的計畫。
一如該計畫的名稱所示，腦部研究進展有賴發展更棒的活腦檢視之道。此事做起來並不容易，但維瑪博士等人的研究證明，這麼做十分值得。（黃維德譯）
©The Economist Newspaper Limited 2013
The Economist
Sex and brains
Vive la
difference!
By The Economist
From The Economist
Published: December 10, 2013
Dec 7th 2013 | From the print edition
A new technique has drawn wiring diagrams of the brains of the two
sexes. The contrast between them is illuminating.
MEN and women do not think in the same ways. Few would disagree with
that. And science has quantified some of those differences. Men, it is pretty
well established, have better motor and spatial abilities than women, and more
monomaniacal patterns of thought. Women have better memories, are more socially
adept, and are better at dealing with several things at once. There is a lot of
overlap, obviously. But on average these observations are true.
Suggesting why they are true in evolutionary terms is a game anyone can
play. One obvious idea is that because, in the days of hunting and gathering,
men spent more time wandering away from camp, their brains needed to be adapted
to able to find their way around. They also spent more time tracking, fighting
and killing things, be they animals or intrusive neighbours. Women by contrast,
politicked among themselves and brought up the children, so they needed to be
adapted to enable them to manipulate each other's and their children's emotions
to succeed in their world.
Finding out why sex differences are true in neurological terms—in other
words, how the brain is wired up to create them—is another matter altogether.
To play this game you have to have a lot of expensive kit, not just a
comfortable chair from which to pontificate. And that is exactly what Ragini
Verma of the University of Pennsylvania and her colleagues do have. As a
result, as they outline in the Proceedings of the National Academy of Sciences,
they have been able to map out differences in the ways male and female brains
are cabled and match them, at least to their own satisfaction, to the
stereotypes beloved of both folklore and psychology.
Sugar and spice or puppy-dogs' tails?
Neurology has been revolutionised over the past couple of decades by a range
of techniques that can scan living brains. Dr Verma's technique of choice is
diffusion tensor imaging. This follows water molecules around the brain.
Because the fibres that connect nerve cells have fatty sheaths, the water in
them can diffuse only along a fibre, not through the sheath. So, diffusion
tensor imaging is able to detect bundles of such fibres, and see where they are
going.
Dr Verma and her team applied the technique to 428 men and boys, and
521 women and girls. Their results are summarised in the two diagrams above,
which show connection trends averaged from the sum of participants' brains.
The two main parts of a human brain are the cerebrum, above and towards
the front, which does the thinking, and the cerebellum, below and towards the
back, which does the acting. Each is divided into right and left hemispheres.
As the diagrams show, in men (the left-hand picture) the dominant connections
in the cerebrum are those, marked in blue, within hemispheres. In women, they
are those, marked in orange, between hemispheres. In the cerebellum (not
visible because it is under the cerebrum), it is the other way around.
What this means is open to interpretation, but Dr Verma's take is that
the wiring differences underlie some of the variations in male and female
cognitive skills. The left and right sides of the cerebrum, in particular, are
believed to be specialised for logical and intuitive thought respectively. In
her view, the cross-talk between them in women, suggested by the wiring
diagrams, helps explain their better memories, social adeptness and ability to
multitask, all of which benefit from the hemispheres collaborating. In men, by
contrast, within-hemisphere links let them focus on things that do not need
complex inputs from both hemispheres. Hence the monomania.
When it comes to the cerebellum, the extra cross-links between
hemispheres in men serve to co-ordinate the activity of the whole sub-organ.
That is important because each half controls, by itself, only one half of the
body. Hence men have better motor abilities—or, in layman's terms, are better
co-ordinated than women.
Dr Verma's other main finding is that most of these differences are not
congenital. Rather, they develop with age. Her volunteers ranged from 8 to 22
years old. The brains of boys and girls aged 8 to 13 demonstrated only a few
differences, though all were of the type that later became pronounced.
Adolescents, those aged 13 to 17, showed more. Young adults, over 17, more
still. Sex differences in brains—those visible to this technique, at least—thus
manifest themselves mainly when sex itself begins to matter.
Dr Verma's work is important not only for what it has shown, but also
as a demonstration of the power of diffusion tensor imaging. Studying the
brain, particularly the living brain, is a uniquely hard scientific problem.
The American government has recently promised to spend serious amounts of money
doing so, through what it dubs the BRAIN initiative—the inevitable contrived
acronym supposedly standing for Brain Research through Advancing Innovative
Neurotechnologies.
As that name suggests, advances in brain research depend on the
development of better ways of looking at brains while they are alive and
firing. This will be hard. But work like Dr Verma's shows the rewards of doing
it.
©The Economist Newspaper Limited 2013
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