TED日本語 - オリバー・サックス: 幻覚が解き明かす人間のマインド

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TED日本語 - オリバー・サックス: 幻覚が解き明かす人間のマインド

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幻覚が解き明かす人間のマインド
What hallucination reveals about our minds
オリバー・サックス
Oliver Sacks

内容

神経科医であり作家でもあるオリバー・サックスがシャルル・ボネ症候群 ‐視覚障害者に生じる正常人が経験する幻覚症状の一種 ‐について語ります。自身の患者が体験した幻覚を心温まる細部に渡って描写しながら、あまり社会には知られていないこの現象の生態学へと案内します。

Script

We see with the eyes, but we see with the brain as well. And seeing with the brain is often called imagination. And we are familiar with the landscapes of our own imagination, our inscapes. We've lived with them all our lives. But there are also hallucinations as well, and hallucinations are completely different. They don't seem to be of our creation. They don't seem to be under our control. They seem to come from the outside, and to mimic perception.

So I am going to be talking about hallucinations, and a particular sort of visual hallucination which I see among my patients. A few months ago, I got a phone call from a nursing home where I work. They told me that one of their residents, an old lady in her 90s, was seeing things, and they wondered if she'd gone bonkers or, because she was an old lady, whether she'd had a stroke, or whether she had Alzheimer's.

And so they asked me if I would come and see Rosalie, the old lady. I went in to see her. It was evident straight away that she was perfectly sane and lucid and of good intelligence, but she'd been very startled and very bewildered, because she'd been seeing things. And she told me -- the nurses hadn't mentioned this -- that she was blind, that she had been completely blind from macular degeneration for five years. But now, for the last few days, she'd been seeing things.

So I said, "What sort of things?" And she said, "People in Eastern dress, in drapes, walking up and down stairs. A man who turns towards me and smiles. But he has huge teeth on one side of his mouth. Animals too. I see a white building. It's snowing, a soft snow. I see this horse with a harness, dragging the snow away. Then,one night, the scene changes. I see cats and dogs walking towards me. They come to a certain point and then stop. Then it changes again. I see a lot of children. They are walking up and down stairs. They wear bright colors, rose and blue, like Eastern dress."

Sometimes, she said, before the people come on, she may hallucinate pink and blue squares on the floor, which seem to go up to the ceiling. I said, "Is this like a dream?" And she said, "No, it's not like a dream. It's like a movie." She said, "It's got color. It's got motion. But it's completely silent, like a silent movie." And she said that it's a rather boring movie. She said, "All these people with Eastern dress, walking up and down, very repetitive, very limited." (Laughter)

And she has a sense of humor. She knew it was a hallucination. But she was frightened. She'd lived 95 years and she'd never had a hallucination before. She said that the hallucinations were unrelated to anything she was thinking or feeling or doing, that they seemed to come on by themselves, or disappear. She had no control over them. She said she didn't recognize any of the people or places in the hallucinations. And none of the people or the animals, well, they all seemed oblivious of her. And she didn't know what was going on. She wondered if she was going mad or losing her mind.

Well, I examined her carefully. She was a bright old lady, perfectly sane. She had no medical problems. She wasn't on any medications which could produce hallucinations. But she was blind. And I then said to her, "I think I know what you have." I said, "There is a special form of visual hallucination which may go with deteriorating vision or blindness. This was originally described," I said, "right back in the 18th century, by a man called Charles Bonnet. And you have Charles Bonnet syndrome. There is nothing wrong with your brain. There is nothing wrong with your mind. You have Charles Bonnet syndrome."

And she was very relieved at this, that there was nothing seriously the matter, and also rather curious. She said, "Who is this Charles Bonnet?" She said, "Did he have them himself?" And she said, "Tell all the nurses that I have Charles Bonnet syndrome." (Laughter) "I'm not crazy. I'm not demented. I have Charles Bonnet syndrome." Well, so I did tell the nurses.

Now this, for me, is a common situation. I work in old-age homes, largely. I see a lot of elderly people who are hearing impaired or visually impaired. About 10 percent of the hearing impaired people get musical hallucinations. And about 10 percent of the visually impaired people get visual hallucinations. You don't have to be completely blind, only sufficiently impaired.

Now with the original description in the 18th century, Charles Bonnet did not have them. His grandfather had these hallucinations. His grandfather was a magistrate, an elderly man. He'd had cataract surgery. His vision was pretty poor. And in 1759, he described to his grandson various things he was seeing.

The first thing he said was he saw a handkerchief in midair. It was a large blue handkerchief with four orange circles. And he knew it was a hallucination. You don't have handkerchiefs in midair. And then he saw a big wheel in midair. But sometimes he wasn't sure whether he was hallucinating or not, because the hallucinations would fit in the context of the visions. So on one occasion, when his granddaughters were visiting them, he said, "And who are these handsome young men with you?" And they said, "Alas, Grandpapa, there are no handsome young men." And then the handsome young men disappeared. It's typical of these hallucinations that they may come in a flash and disappear in a flash. They don't usually fade in and out. They are rather sudden, and they change suddenly.

Charles Lullin, the grandfather, saw hundreds of different figures, different landscapes of all sorts. On one occasion, he saw a man in a bathrobe smoking a pipe, and realized it was himself. That was the only figure he recognized. On one occasion when he was walking in the streets of Paris, he saw -- this was real -- a scaffolding. But when he got back home, he saw a miniature of the scaffolding six inches high, on his study table. This repetition of perception is sometimes called palinopsia.

With him and with Rosalie, what seems to be going on -- and Rosalie said, "What's going on?" -- and I said that as you lose vision, as the visual parts of the brain are no longer getting any input, they become hyperactive and excitable, and they start to fire spontaneously. And you start to see things. The things you see can be very complicated indeed.

With another patient of mine, who, also had some vision, the vision she had could be disturbing. On one occasion, she said she saw a man in a striped shirt in a restaurant. And he turned around. And then he divided into six figures in striped shirts, who started walking towards her. And then the six figures came together again, like a concertina. Once, when she was driving, or rather, her husband was driving, the road divided into four and she felt herself going simultaneously up four roads.

She had very mobile hallucinations as well. A lot of them had to do with a car. Sometimes she would see a teenage boy sitting on the hood of the car. He was very tenacious and he moved rather gracefully when the car turned. And then when they came to a stop, the boy would do a sudden vertical takeoff,100 foot in the air, and then disappear.

Another patient of mine had a different sort of hallucination. This was a woman who didn't have trouble with her eyes, but the visual parts of her brain, a little tumor in the occipital cortex. And, above all, she would see cartoons. These cartoons would be transparent and would cover half the visual field, like a screen. And especially she saw cartoons of Kermit the Frog. (Laughter) Now, I don't watch Sesame Street, but she made a point of saying, "Why Kermit?" She said, "Kermit the Frog means nothing to me. You know, I was wondering about Freudian determinants. Why Kermit? Kermit the Frog means nothing to me."

She didn't mind the cartoons too much. But what did disturb her was she got very persistent images or hallucinations of faces and as with Rosalie, the faces were often deformed, with very large teeth or very large eyes. And these frightened her. Well, what is going on with these people? As a physician, I have to try and define what's going on, and to reassure people, especially to reassure them that they're not going insane.

Something like 10 percent, as I said, of visually impaired people get these. But no more than one percent of the people acknowledge them, because they are afraid they will be seen as insane or something. And if they do mention them to their own doctors they may be misdiagnosed.

In particular, the notion is that if you see things or hear things, you're going mad, but the psychotic hallucinations are quite different. Psychotic hallucinations, whether they are visual or vocal, they address you. They accuse you. They seduce you. They humiliate you. They jeer at you. You interact with them. There is none of this quality of being addressed with these Charles Bonnet hallucinations. There is a film. You're seeing a film which has nothing to do with you, or that's how people think about it.

There is also a rare thing called temporal lobe epilepsy, and sometimes, if one has this, one may feel oneself transported back to a time and place in the past. You're at a particular road junction. You smell chestnuts roasting. You hear the traffic. All the senses are involved. And you're waiting for your girl. And it's that Tuesday evening back in 1982. And the temporal lobe hallucinations are all-sense hallucinations, full of feeling, full of familiarity, located in space and time, coherent, dramatic. The Charles Bonnet ones are quite different.

So in the Charles Bonnet hallucinations, you have all sorts of levels, from the geometrical hallucinations -- the pink and blue squares the woman had -- up to quite elaborate hallucinations with figures and especially faces. Faces, and sometimes deformed faces, are the single commonest thing in these hallucinations. And one of the second commonest is cartoons.

So, what is going on? Fascinatingly, in the last few years, it's been possible to do functional brain imagery, to do fMRI on people as they are hallucinating. And in fact, to find that different parts of the visual brain are activated as they are hallucinating. When people have these simple geometrical hallucinations, the primary visual cortex is activated. This is the part of the brain which perceives edges and patterns. You don't form images with your primary visual cortex.

When images are formed, a higher part of the visual cortex is involved in the temporal lobe. And in particular,one area of the temporal lobe is called the fusiform gyrus. And it's known that if people have damage in the fusiform gyrus, they maybe lose the ability to recognize faces. But if there is an abnormal activity in the fusiform gyrus, they may hallucinate faces, and this is exactly what you find in some of these people. There is an area in the anterior part of this gyrus where teeth and eyes are represented, and that part of the gyrus is activated when people get the deformed hallucinations.

There is another part of the brain which is especially activated when one sees cartoons. It's activated when one recognizes cartoons, when one draws cartoons, and when one hallucinates them. It's very interesting that that should be specific. There are other parts of the brain which are specifically involved with the recognition and hallucination of buildings and landscapes.

Around 1970, it was found that there were not only parts of the brain, but particular cells. "Face cells" were discovered around 1970. And now we know that there are hundreds of other sorts of cells, which can be very, very specific. So you may not only have "car" cells, you may have "Aston Martin" cells. (Laughter) I saw an Aston Martin this morning. I had to bring it in. And now it's in there somewhere. (Laughter)

Now, at this level, in what's called the inferotemporal cortex, there are only visual images, or figments or fragments. It's only at higher levels that the other senses join in and there are connections with memory and emotion. And in the Charles Bonnet syndrome, you don't go to those higher levels. You're in these levels of inferior visual cortex where you have thousands and tens of thousands and millions of images, or figments, or fragmentary figments, all neurally encoded in particular cells or small clusters of cells.

Normally these are all part of the integrated stream of perception, or imagination, and one is not conscious of them. It is only if one is visually impaired or blind that the process is interrupted. And instead of getting normal perception, you're getting an anarchic, convulsive stimulation, or release, of all of these visual cells in the inferotemporal cortex. So, suddenly you see a face. Suddenly you see a car. Suddenly this, and suddenly that. The mind does its best to organize and to give some sort of coherence to this, but not terribly successfully.

When these were first described, it was thought that they could be interpreted like dreams. But in fact people say, "I don't recognize the people. I can't form any associations." "Kermit means nothing to me." You don't get anywhere thinking of them as dreams.

Well, I've more or less said what I wanted. I think I just want to recapitulate and say this is common. Think of the number of blind people. There must be hundreds of thousands of blind people who have these hallucinations, but are too scared to mention them. So this sort of thing needs to be brought into notice, for patients, for doctors, for the public. Finally, I think they are infinitely interesting and valuable, for giving one some insight as to how the brain works.

Charles Bonnet said,250 years ago -- he wondered how, thinking these hallucinations, how, as he put it, the theater of the mind could be generated by the machinery of the brain. Now,250 years later, I think we're beginning to glimpse how this is done. Thanks very much.

(Applause)

Chris Anderson: That was superb. Thank you so much. You speak about these things with so much insight and empathy for your patients. Have you yourself experienced any of the syndromes you write about?

Oliver Sacks: I was afraid you'd ask that. (Laughter) Well, yeah, a lot of them. And actually I'm a little visually impaired myself. I'm blind in one eye, and not terribly good in the other. And I see the geometrical hallucinations. But they stop there.

CA: And they don't disturb you? Because you understand what's doing it, it doesn't make you worried?

OS: Well they don't disturb me any more than my tinnitus, which I ignore. They occasionally interest me, and I have many pictures of them in my notebooks. I've gone and had an fMRI myself, to see how my visual cortex is taking over. And when I see all these hexagons and complex things, which I also have, in visual migraine, I wonder whether everyone sees things like this, and whether things like cave art or ornamental art may have been derived from them a bit.

CA: That was an utterly, utterly fascinating talk. Thank you so much for sharing.

OS: Thank you. Thank you. (Applause)

人は目だけではなく 脳でも見ています 想像は脳で見るものです 想像が描き出す心象は馴染みがあるでしょう どんな人だって想像はしますから しかし 幻覚もあります 幻覚は全く異なるもので 我々の創造ではありません 抑制もできません 幻覚は外から現れて 現実と区別がつきにくい

その幻覚について話をします 私の患者が体験した- 特殊な幻視を紹介します 数か月前に電話がありました 私が働く老人ホームからです 入居中の90代の女性が 幻覚を見ているので 気が狂ったのではないか と または 高齢のために 脳卒中かアルツハイマーではないか と

それで診に来てほしいと頼まれました ロザリーおばあさんです 診に行ったら 彼女が正気なのは 明らかでした 頭ははっきりしていて 理解力もある でも非常に当惑していました 幻覚が現れるからです 事前に聞いていませんでしたが 彼女は盲目だったのです 彼女は5年前に 加齢黄斑変性症のため 失明したのですが 数日前から幻覚を見るようになりました

“何が見える?” と聞くと “東洋風の服を着た人たちが 階段を上り下りしている 私の方を見て微笑んでいる男 口の脇から大きな歯が出ているの 動物も見える 白い建物  わた雪が降っている 雪かき用ハーネスをつけた馬が見える そして ある晩 シーンが変わったの 猫や犬が寄ってきて ある程度近づいたら立ち止まる そして また変わる 階段を上り下りしている たくさんの子ども バラ色や青の明るい服を着ている 東洋の服のよう”

その人たちが現れる前に 床に広がるピンクと青の四角い模様が 天井に上がる幻覚が見えることも “夢のような感じ?” と尋ねると “いいえ  夢ではなく映画のよう 色もついていて 動きがある でも無声映画のように音がない” やや退屈な映画だ と “東洋風の服をまとった人たちは 上り下りを繰り返すばかりで 行動が限られている” (笑)

ユーモアのある女性なんです 幻覚だとわかっていても 怖がっていた 95年の人生で 幻覚を見たことがなかったから その幻覚は彼女の思考や感覚 行動と無関係だというのに やって来ては消えていくようです コントロールすることはできず 彼女には幻覚の中の 人物や場所は どれも見覚えがない しかも人も動物も 彼女に気がついていないようだった 彼女は状況が把握できず 狂ってしまったかと 心配していました

私は入念に診察しました 陽気なおばあさんで 異常はなし 体調良好 幻覚を引き起こす薬も飲んでいません 盲目ということだけ それで 言ったんです “察しがつきました 視力低下や失明によって起きる- 特殊な幻視があるんです” “これはシャルル ボネという男性が 18世紀に初めて 記述した症状です あなたはシャルルボネ症候群です 脳も精神も正常 シャルルボネ症候群ですよ”

それを聞いて彼女は安心し 深刻な問題ではないことにホッとした そして むしろ 好奇の目で “シャルルボネって誰? 彼にも幻覚が見えたの?” と さらには “看護師のみんなに 私はシャルルボネ症候群だと言ってちょうだい” (笑) “狂ってもボケてもいない  シャルルボネ症候群なだけ” 彼女の言うとおりにしました

これは よくあるケースです 主として老人ホームで仕事をするので 高齢者が相手です 聴覚 視覚障害者も多く 聴覚障害者の約1割は 音楽性幻聴が聴こえます 視覚障害者の約1割は 幻視を見ます 全盲ではなく 弱視も含まれます

18世紀に話を移しますが この幻覚症状があったのは シャルルボネではなく彼の祖父でした 祖父は高齢の裁判官でした 白内障の手術を受け 視力は相当悪かった 1759年 彼は自分の幻覚症状を 孫に話したのです

まず彼が話したのは 宙に浮くハンカチです 大判で青地に オレンジの丸が4つ 祖父は幻覚だと認識していました 宙に浮くハンカチはありませんから そして宙に浮く大きな車輪を見た でも 時々 幻覚か否か自信がなかった 幻覚が身の回りのものと 調和しているからです ある日 孫娘が来ていた時 “男前の若い衆は誰かね?” と聞きました “まぁ お祖父様 そんな人いないわ” そうすると その男たちは姿を消しました 幻覚ではよくあることです パッと現れ パッと消える 徐々に現れたり消えたりしません むしろ突然起きるのです

シャルルボネの祖父には 何百もの人影や形 風景が見えました バスローブ姿でパイプを吸う男も見えました それは彼自身だったのです 見覚えのあるのは それだけでした ある時 パリの街を歩いていたら 目に入った本物の工事現場の足場が 帰宅すると15cmのミニチュアとなって 書斎の机にのっていました 映像を繰返し見ることは 反復視と呼ばれます

シャルルボネの祖父やロザリーに 起こっている現象を ロザリーに説明しました 視力を失うと 脳の視覚部分に 入る情報が無くなるため そこが活動過多になります そして自発的に作用してしまい 幻覚を見始めるのです 時に内容も非常に複雑化します

別の患者の体験です その女性は弱視で 彼女に見えるものは厄介でした ある時 彼女はレストランで 縞模様のシャツを着た男を見た 男は彼女の方を振り向き 6人に分離して 彼女の方へと 歩き始めたのです そして 6人はスーっと1人に戻りました ある時 彼女は夫が運転する- 車に乗っていたら 道が4つに分かれました そして彼女も4つに分かれて進む感覚を覚えました

動きのある幻覚も見えました その多くは車に関連したものでした 時々彼女はボンネットに座っている― 10代の男の子が見えました 車にくっつき 道を曲がるたびに 優雅に動くのです そして 車が止まると 男の子は 30m 真上に急上昇して 姿を消してしまうのです

こんな幻覚を見る患者もいました その女性は目には問題ないけれど 脳の視覚部分に問題がありました 後頭皮質にある小さな腫瘍です とりわけ 彼女にはアニメ映像が見えました そのアニメは透けて見えるもので 画面のように視野の半分を占めています よく見るのはカエルのカーミットでした (笑) 私はセサミストリートは見ませんが 彼女は こう主張するんです “なぜ?カーミットが出てくる理由がわからない フロイト的な意味が知りたい なぜカーミットなの? 何の意味もなさないのに”

アニメは我慢できても しつこく出てくるイメージや顔の幻覚に 彼女もロザリーも困っていました 多くの場合 巨大な歯や目をした デフォルメされた顔が見えるからです 彼女は怖がっていました 彼らには何が起きていたのでしょう 医者である私は患者の症状を見極め 安心させるのが仕事です 狂ったのではないと伝えるのは特にそうです

先ほども言いましたが 視覚障害者の 1割がこの症状を持っています しかし 症状を訴えるのは そのうちの1%以下 精神障害だと思われるのが怖いからです 病院に行っても誤診される- 可能性だってあります

特に 幻覚の概念は 気が狂ってる とみられがちです しかし 精神病性幻覚は かなり違います 精神病性の幻視や幻聴の場合 声をかけてくる 責められる 誘惑してくる 侮辱される 馬鹿にされる 巻き込まれてしまいます シャルルボネ症候群において 声をかけられることはありません 自分とは無関係の映画を見るようなもの そのように 捉えられています

側頭葉てんかん という稀なケースがあります この症状は 過去に遡る感覚や 以前訪れた場所へ戻るような 感覚が生じることがあります ある交差点に立っている 焼き栗の香りがする 車の音 五感で感じ取れます 彼女を待っていた- 忘れもしない1982年 あの火曜の夜 側頭葉に関わる幻覚は すべての感覚に関係しています 感覚があり 馴染みがあり 場所や時間もはっきりしていて 話に筋が通っていて芝居のよう シャルルボネは かなり違います

シャルルボネ症候群には 様々なレベルがあります 幾何学模様の幻覚や ロザリーが見たピンクや青の四角 人や 特に顔の出てくる とても精緻な幻覚もあります デフォルメされた顔が現れるのは シャルルボネ症候群で 最も一般的です 2つ目によくあるのはアニメ

これは どういうことか 面白いことに過去数年の間に 幻覚症状の最中にfMRIを使用して 脳機能の画像化が可能になりました 実際に幻覚が現れているときに 異なる脳の視覚部分が 活発化することが特定されました 単純な幾何学模様が現れるときは 一次視覚野が活発化します 脳は この領域でへりや模様を知覚します 一次視覚野で画像を作りだすのではありません

画像が作りだされるとき 高次の視覚野が 側頭葉と作用します 特に 側頭葉の一部は 紡錘状回と呼ばれています 紡錘状回がダメージを受けると 顔を認識できなくなることがあります しかし紡錘状回が異常に働くと 顔の幻覚を見ることがあります これが 患者に起きていることだったのです この脳回の前方には 歯と目を思い描く領域があります 巨大な歯と目の幻覚が見えるときは 脳回のその部分が活発化しています

脳の別の部分は アニメが見えるときに 活発になります アニメを見たり描いたり アニメの幻覚発生時に活動しています 特異性があって興味深いんです 脳の他の部分では具体的に 建物 風景の認識や幻覚に 関連する部分があります

1970年頃 脳の決まった部分のみならず 特定の細胞があることがわかりました 1970年頃 顔細胞が発見されました 今では何百種類もの 細胞が発見されています 非常に特有な細胞です ですから もしかしたら 車細胞だけではなく アストンマーチン細胞があるかも (笑) 今朝アストンマーチンを見たので 話したかったんだ 既に どこかにあるはずだよ (笑)

下側頭葉皮質と呼ばれる このレベルでは 視覚画像や断片しか 処理されません 他の感覚が加わってくるのは もっと高次の領域です そして記憶や感情と関連しています シャルルボネ症候群では このレベルまでは達しません 下側頭葉皮質において 何千も 何百万もの イメージや断片的な作り事が 決まった細胞や 細胞の小さな固まりに 神経符号化される部分で生じます

通常 これはどれも知覚や想像の 一体化した流れの一部なのです 人間は意識していません 視覚障害者である場合に限り この過程が中断されます そして 正常な知覚を得る代わりに 下側頭葉皮質では その視覚細胞から 無秩序で発作的な刺激や 放出が行われているのです そして突然 顔や車が見えたり 色々なものが見えるのです 頭はまとめようとしたり 一貫性をもたせようと頑張りますが 完璧には働きません

この幻覚が初めて発表されたとき 夢のように解釈できると思われていました でも 患者さんは言う “こんな人たち知らない 関連づけ出来ないわ” “カーミットなんて私にとって何の意味も持たない” 夢のように考えてもダメなんです

さぁ 私の話はこんなところです 要は この幻覚症状は よくある事なんです 世界の盲人数を考えてください このような幻覚症状を持つ盲人は 何十万といるに違いない でも怖くて言えないんです ですから このような事実は患者 医者 世間のために もっと知られるべきなんです 最後に これは 脳の働きを洞察するには 非常に興味深く 貴重な情報だと思っています

250年前にシャルルボネは このような幻覚症状を思いながら 脳の機械仕掛けから 心の劇作品が いかに作り出されるのだろうと考えました 250年経った現在 私たちは 真相を究明し始めた と思うのです どうもありがとう

(拍手)

最高だ どうもありがとう 洞察力が深くて 患者さんへの 共感が感じられました そのような経験を ご自身もされたことは?

聞かれるだろうと思いましたよ (笑) けっこう見ます 実は私も視覚障害者です 片目は失明して もう片方も良好ではありません 幾何学模様の幻覚が見えます 他のは見えません

不安にかられませんか? どんなことが起きているのか分っておられるから

耳鳴りよりは ましです 耳鳴りは無視してますけど 幻覚には時折興味が湧くので ノートにたくさん絵を描いています fMRIも使用して視覚野の 機能も見ました 六角形や複雑な模様は 眼性片頭痛でも 見ることがあるのですが これは普通なのでしょうかね そして洞窟壁画や装飾デザインは 幻覚をヒントに作られたのか興味があります

非常に興味深い貴重な講話でした どうもありがとうございました

ありがとうございました (拍手)

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