字幕表 動画を再生する
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Today I want to tell you about a project being carried out by scientists all over the world
翻訳: Reiko Bovee 校正: Eriko T
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to paint a neural portrait of the human mind.
今日お話ししたい事は
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And the central idea of this work
世界中の科学者が行っている
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is that the human mind and brain is not a single, general-purpose processor,
あるプロジェクト
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but a collection of highly specialized components,
ヒトの脳の神経が描く像についてです
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each solving a different specific problem,
この研究の中心となる考えは
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and yet collectively making up who we are as human beings and thinkers.
ヒトの思考と脳は
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To give you a feel for this idea, imagined the following scenario:
汎用な単一目的の プロセッサ―なのではなく
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You walk into your child's daycare center.
高度に特殊化された 各部の複合体であり
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As usual, there's a dozen kids there, waiting to get picked up.
その1つ1つが各々 固有の問題を解決しながらも
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But this time, the children's faces look weirdly similar,
総合的に
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and you can't figure out which child is yours.
思考する我々を 作っているという事です
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Do you need new glasses?
これを理解する為
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Are you losing your mind?
次のシナリオを想像してみて下さい
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You run through a quick mental checklist.
あなたは自分の子供がいる 保育所に入って行きます
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No, you seem to be thinking clearly,
いつものように何十人もの子どもがいて
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and your vision is perfectly sharp.
親の迎えを待っていますが
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And everything looks normal, except the children's faces.
今日は
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You can see the faces, but they don't look distinctive,
子ども達の顔が奇妙に同じに見えます
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and none of them looks familiar,
どの子が自分の子なのか 見分けがつきません
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and it's only by spotting an orange hair ribbon that you find your daughter.
新しい眼鏡がいるのでしょうか?
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This sudden lost of the ability to recognize faces actually happens to people.
気がおかしくなったのでしょうか?
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It's called prosopagnosia,
素早く色々な事が頭をよぎります
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and it results from damage to a particular part of the brain.
いいえ頭ははっきりしていて
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The striking thing about it is that only face recognition is impaired,
目も問題なく良く見えています
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everything else is just fine.
全てがまともなのに
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So prosopagnosia is one of many surprisingly specific mental deficits that can happen after brain damage.
子供達の顔だけがそうでないのです
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These syndromes collectively have suggested for a long time
顔は見えるのですが
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that the mind is divvied up into distinct components,
区別ができず
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but the effort to discover those components has jumped to warp speed
どの子も覚えのない顔なのです
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with the invention of brain imaging technology,
オレンジ色のリボンを見つけて
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especially MRI.
ようやくそれが自分の子供だと分かります
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So MRI enables you to see internal anatomy at high resolution.
このように急に顔を 認識できなくなることが
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So I'm going to show you in a second
実際起きるのです
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a set of MRI cross-sectional images through a familiar object,
それは相貌失認と呼ばれ
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and we're going to fly through them and you're going to try to figure out what the object is. Here we go.
脳のある特定の場所に
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It's not that easy. It's an artichoke.
障害が起きた結果起きます
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Okay let's try another one,
これに驚かされる事は
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starting from the bottom and going through the top.
顔認知だけに障害があり
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Broccoli! It's a head of broccoli. It's it beautiful? I love that.
その他は問題がない事です
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Okay here's another one.
相貌失認は脳損傷後におきる
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It's a brain, of course. In fact, it's my brain.
数々の 驚くほど特異な 脳機能障害の1つです
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We're going through slices through my head like that.
このような症状などを総合して
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That's my nose over on the right, and now we're going over here. Right there.
脳は明確に役割が分担された領域別に
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So this picture is nice,
分かれている事が長い間 示唆されていたのですが
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if I do say so myself.
それ等の領域を探求する研究に
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But it shows only anatomy.
一気に進歩をもたらしたのは
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The really cool advance with functional imaging happened when scientists figured out
脳画像技術に於ける発明—
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how to make pictures that show not just anatomy but activity,
特にMRIです
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that is, where neurons are firing.
MRIを使い脳内部の組織構造を
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So here's how this works.
高解度画像で見ることができます
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Brains are like muscles. When they get active,
MRIの断面画像を
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they need increased blood flow to supply that activity,
MRIの断面画像を
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and lucky for us, blood flow control to the brain is local.
よくご存知のものを通して
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So if a bunch of neurons, say, right there get active and start firing,
お見せしましょう
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then blood flow increases just right there.
その物とは何か分かるでしょうか
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So functional MRI picks up on that blood flow increase,
これです
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producing a higher MRI response where neural activity goes up.
分かり難いですが アーティチョークです
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So to give you a concrete feel for how a functional MRI experiment goes
ではこれはどうでしょう
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and what you can learn from it and what you can't,
下から上まで行きますよ
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let me describe one of the first studies I ever did.
ブロッコリーの頭です!
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We wanted to know if there was a special part of the brain for recognizing faces,
綺麗でしょう?私は好きです
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and there was already reason to think there might be such a thing
もう1つ 勿論これはヒトの脳です
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based on this phenomenon of prosopagnosia that I described a moment ago.
実はこれは私の脳です
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But nobody had ever seen that part of the brain in a normal person,
私の脳をスライスして行きます
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so we set out to look for it.
右の方に鼻があり
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So I was the first subject.
今ここに来ました ちょうどここです
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I went into the scanner, I lay on my back,
この画像はいいですね 自分でも本当にそう思いますが
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I held my head as still as I could while staring at pictures of faces
組織を映し出してるだけに過ぎません
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like these
機能画像という本当にすごい進歩は
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and objects like these
科学者が組織だけでなく
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and faces… and objects… for hours.
活動 すなわちニューロンの発火を 捉える技術を
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So as somebody who has pretty close to the world record of total number of hours spent inside a MRI scanner,
編み出した時に起きました
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I can tell you that one of the skills that's really important for MRI research
それは このような働きをします
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is bladder control.
脳は筋肉の様なもので
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When I got out of the scanner, I did a quick analysis of the data,
活発な時は
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looking for any parts of my brain that produced a higher response when I was looking at faces than when I was looking at objects,
その活動の為に 送り込む血量を増やします
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and here's what I saw.
幸いに脳の血流制御は 局部的なので
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Now, this image looks just awful by today's standards,
例えばここで 多くのニューロンが
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but at the time I thought it was beautiful.
活発に発火し始めたら
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What it shows is that region right there, that little blob,
そこの血流は増します
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it's about the size of an olive
fMRIはその血流の 増加をキャッチし
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and it's on the bottom surface of my brain about an inch straight in from right there.
ニューロンが活性化した箇所で
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And what that part of my brain is doing is producing a higher MRI response,
高反応を示します
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that is, higher neural activity, when I was looking at faces
具体的に
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than when I was looking at objects.
fMRIの実験が如何に行われるか
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So that's pretty cool.
そこからどんな事が分かるか
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But how do we know this isn't a fluke?
又 分からないかを説明するため
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Well, the easiest way is to just do the experiment again.
最初の研究の1つを お話しします
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So I got back in the scanner, I looked at more faces and I looked at more objects
我々が知りたかったのは 顔認知だけの領野があるかどうかです
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and I got a similar blob.
既に その存在は
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And then I did it again,
お話しした相貌失認に基づき
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I did it again and again and again,
推察されてはいましたが
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and around about then I decided to believe it was for real.
健常者の脳にそれを確認した者は
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But still, maybe this is something weird about my brain
誰もいませんでした
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and no one else has one of these things in there.
それで我々はその探索に 乗り出しました
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So to find out, we scanned a bunch of other people and found that
私が最初の実験台になり
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pretty much everyone has that little face-processing region
MRI 内に入り横たわりました
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in a similar neighbourhood of the brain.
頭を出来るだけ動かさず
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So the next question was, what does this thing really do?
このような顔や物を
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Is it really specialized just for face recognition?
何時間も見つめました
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Well, maybe not, right?
何時間も見つめました
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Maybe it responds not only to faces but to any body part.
私は fMRIスキャナーの中で
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Maybe it responds to anything human or anything alive or anything round.
費やした時間の合計が 世界記録に
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The only way to be really sure that that region is specialized for face recognition
近いと思いますが
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is to rule out all those hypotheses.
この研究で 本当に大切なスキルの一つは
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So we spent much of the next couple of years
膀胱制御でした
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scanning subjects while they looked at lots of different kinds of images,
(笑)
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and we showed that that part of the brain responds strongly when you look at any images that are faces of any kind,
スキャナーから出た時
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and it responds much less strongly to any image you show that isn't a face, like some of these.
データをすぐに分析して
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So have we finally nailed the case that this region is necessary for face recognition?
私の脳の中で
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No, we haven't.
顔を見ている時に 物体を見たときよりも
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Brain imaging can never tell you if a region is necessary for anything.
強い反応を示す箇所を探しました
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All you can do with brain imaging is watch regions turn on and off as people think different thoughts.
これが私が見たものです
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To tell if a part of the brain is necessary for a mental function,
この画像は今の基準からすると ひどいもののように見えますが
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you need to mess with it and see what happens,
当時は美しいものだと思いました
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and normally we don't get to do that.
小さな塊が見える
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But an amazing opportunity came about
箇所がありますが
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very recently when a couple of colleagues of mine tested this man who has epilepsy
オリーブサイズ位で
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and who is shown here in this hospital bed
私の脳表面の下部—
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where he's just had electrodes placed on the surface of his brain
ここから約2.5cm真っすぐ中に 入った所です
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to identify the source of his seizures.
脳のその箇所が示しているのは
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So it turned out by total chance that
強い fMRI反応 つまり
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two of the electrodes happen to be right on top of this face area.
非常に活発な脳の神経の活動です
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So with the patient's consent,
私が 物体でなく
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the doctors asked him what happened when they electrically stimulated that part of his brain.
人の顔写真を見ている時のものです
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Now, the patient doesn't know where those electrodes are,
かなり面白いのですが
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and he's never heard of the face area.
何故これが偶然でないと 分かるのでしょう?
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So let's watch what happens.
では最も簡単な方法は
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It's going to start with a control condition that will say “Sham”
実験をもう一度やってみる事です
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nearly invisibly in red in the lower left,
私はMRIスキャナーに戻り
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when no current is delivered,
もっと顔や物の写真を見ました
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and you'll hear the neurologist speaking to the patient first. So let's watch.
そして同じ様な斑点が見られました
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Okay, just look at my face and tell me what happens when I do this. Alright?
それからもう一度やり
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One, two three.
又同じ結果がでました
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Nothing. –Nothing?
もう一度 もう一度と
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Okay, I'm going to do it one more time.
もうその頃には
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Look at my face
これは本物だと 信じる事にしました
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One, two, three.
しかし これは私の脳が 何かおかしいからであり
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You just turned into somebody else.
他の誰にも こういう事は 起きないのかもしれないと
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Your face metamorphosed.
他の多くの人達も スキャンして調べると
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Your nose got saggy. It went to the left.
殆ど同じ結果で
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You almost looked like somebody I'd seen before, but somebody different.
小さな顔領域が 誰でも
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That was a trip.
同じ様な部位にありました
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So this experiment…
それで次にくる疑問は
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This experiment finally nails the case
この箇所の機能です
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that this region of the brain is not only selectively responsive to faces,
顔認知だけでしょうか? そうでないかもしれませんね
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but causally involved in face perception.
顔認知だけでしょうか? そうでないかもしれませんね
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that this region of the brain is not only selectively responsive to faces,
人の顔だけに反応するのでなく
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to really establish that a part of the brain is selectively involved in a specific mental process.
他の身体部分にも 反応するかもしれません
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Next, I'll go through much more quickly some of the other specialized regions of the brain that we and others have found.
人の様な物や他の生物や
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So to do this, I've spent a lot of time in the scanner over the last month
丸っこい物にも
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so I can show you these things in my brain.
反応するかもしれません
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So let's get started.
その領域が顔の認知に 特化して機能する事を
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Here's my right hemisphere. So we're oriented like that.
はっきり確かめる唯一の方法は
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You're looking at my head this way. Imagine taking the skull off and looking at the surface of the brain like that.
仮説を全て除外していく事です
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Okay, now as you can see, the surface of the brain is all folded up.
そこで我々はそれから数年
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So that's not good. Stuff could be hidden in there. We want to see the whole thing.
色々な写真を見る人々の脳を
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So let's inflate it so we can see the whole thing.
スキャンして
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Next, let's find that face area I've been talking about that responds to images like these.
何の顔であろうと
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To see that, let's turn the brain around and look on the inside surface on the bottom,
顔の写真を見ている時は
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and there it is, that's my face area.
顔以外の写真の時と比べて
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Just to the right of that is another region that is shown in purple
脳のその領野が
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that responds when you process color information.
強く反応しているのが
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And near those regions are other regions that are involved in perceiving places,
観察されました
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like right now I'm seeing this layout of space around me,
これで我々は
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and these regions in green right there are really active.
ここは顔認知に必要な領域だと 決定づけたのでしょうか
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There's another one out on the outside surface again
いいえ そうではありません
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where there's a couple more face regions as well.
脳画像だけでは 特定の領野が
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Also in this vicinity is a region that's selectively involved in processing visual motion,
特定の機能に必要かどうかは 分からないのです
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like these moving dots here,
脳画像で私たちが出来る事は
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and that's in yellow at the bottom of the brain.
様々な思考で あらゆる領野のニューロンが
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And near that is a region that responds when you look at images of bodies and body parts like these,
活性・不活性化されるのを 見るだけです
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and that region is shown in lime green at the bottom of the brain.
脳の一部がある心的機能に 必要かどうかを見るには
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Now all these regions I've shown you so far
そこを刺激して 反応を見る必要がありますが
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are involved in specific aspects of visual perception.
普段そういう事はできません
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Do we also have specialized brain regions for other senses, like hearing?
しかし最近驚くべき機会が巡ってきて
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Yes, we do. So if we turn the brain around a little bit,
私の同僚数人が
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here's a region in dark blue that we recorded just a couple of months ago,
癲癇持ちのある男性を テストしました
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and this region responds strongly when you hear sounds with pitch, like these.
これが病院のベットに 横たわるその男性です
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Okay? In contrast, that same region does not respond strongly when you hear perfectly familiar sounds that don't have a clear pitch, like these.
脳の表面に
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Next to the pitch region is another set of regions that are selectively responsive when you hear the sounds of speech.
癲癇の源を特定するための
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Okay, now let's look at these same regions.
電極が 配置されたばかりです
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In my left hemisphere, there's a similar arrangement, not identical, but similar,
全く偶然に
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and most of the same regions are in here,
電極の二つが
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albeit sometimes different in size.
顔認知領域の上部に 配置されていました
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Now, everything I've shown you so far
それで患者の同意を得て
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are regions that are involved in different aspects of perception, vision and hearing.
医師達は
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Do we also have specialized brain regions for really fancy, complicated mental processes?
脳のその部位を電気で刺激して どうなるか彼に尋ねました
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Yes, we do. So here in pink are my language regions.
患者はどこに電極が あるのか知りませんし
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So it's been known for a very long time that that general vicinity of the brain is involved in processing language.
患者はどこに電極が あるのか知りませんし
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But we showed very recently that these pink regions respond extremely selectively.
顔認知領域の事など 聞いた事もありません
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They respond when you understand the meaning of a sentence,
では どうなるか見てみましょう
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but not when you do other complex mental things
比較用の条件から始めます
-
like mental arithmetic or holding information in memory
殆ど見えないくらい「Sham」と
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or appreciating the complex structure in a piece of music.
左下に赤く
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The most amazing region that's been found yet is this one right here in turquoise.
電気が流されてない時に 出てきます
-
This region responds when you think about what another person is thinking.
神経学者が患者にまず 話しかけているが聞こえます
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So that may seem crazy, but actually we humans do this all the time.
神経学者:「私の顔を見て下さい
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You're doing this when you realize that your partner is going to be worried if you don't call home to say you're running late.
こうした時に 何が起きるか言って下さい
-
I'm doing this with that region of my brain right now
いいですか?」
-
when I realize that you guys are probably now wondering about all that gray, uncharted territory in the brain, what's up with that?
患者:「OK」
-
Well, I'm wondering about that too,
神経学者:「1、2、3」
-
and we're running a bunch of experiments in my lab right now
患者:「何も起きません」 神経学者:「何も?Ok」
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to try to find a number of other possible specializations in the brain for other very specific mental functions.
神経学者:「もう一度します
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But importantly, I don't think we have specializations in the brain for every important mental function,
私の顔を見て
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even mental functions that may be critical for survival.
1、2、3」
-
In fact, a few years ago,
患者:「他の誰かになっただけです
-
there was a scientist in my lab who became quite convinced that he'd found a brain region for detecting food,
顔が変形して
-
and it responded really strongly in the scanner when people look at images like this.
鼻が下がり左に行き
-
And further, he found a similar response in more or less the same location in 10 out of 12 subjects.
見た事がある様な 他の人みたいになりました
-
So he was pretty stoked and he was running around the lab
でも全く他の誰かです
-
telling everyone that he was going to go on Oprah with his big discovery.
ドラッグでもやったようでした」
-
But then he devised the critical test.
(笑)
-
He showed subjects images of food like this
この実験が・・・
-
and compared them to images with very similar color and shape, but that weren't food, like these,
(拍手)
-
and his region responded the same to both sets of images.
この実験で ついに確定したことは
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So it wasn't a food area. It was just a region that liked colors and shapes.
この脳の領域は
-
So much for Oprah.
顔だけに反応するのでなく
-
But then the question, of course, is,
顔を認識する為に無くてはならないものだという事です
-
how do we process all this other stuff that we don't have specialized brain regions for?
こうして顔認知領域に関しての 詳細を見てきたのは
-
Well, I think the answer is that, in addition
脳には特定の思考過程に関与する
-
to these highly specialized components that I've been describing,
領域がある事を確定するには
-
we also have a lot of very general-purposed machinery in our heads
どのようにする必要があるのかを お伝えする為です
-
that enables us to tackle whatever problem comes along.
次にもっと端的に
-
In fact, we've shown recently that these regions here in white
今までに発見された 機能が分化した脳領域
-
respond whenever you do any difficult mental task at all,
に関してお話しします
-
well, of the seven that we've tested.
この為に私は先月
-
So each of the brain regions that I've described to you today
fMRIの中で 時間を随分費やしたので
-