What happens when you have a concussion? - Clifford Robbins

脳震盪が起こるとどうなるのか - クリフォード・ロビンズ

翻訳: Mayumi Oiwa-Bungard 校正: Masaki Yanagishita

Each year in the United States,

アメリカでは

players of sports and recreational activities

スポーツ レクリエーション関連の脳震盪が

receive between 2.5 and 4 million concussions.

年に250ー400万回起こるとされています

How dangerous are all those concussions?

脳震盪はどれだけ危険なのか？

The answer is complicated,

答えは複雑

and lies in how the brain responds when something strikes it.

脳が衝撃にどう反応するかにより異なります

The brain is made of soft fatty tissue, with a consistency something like jello.

脳はゼリーのように柔らかい 脂肪性の組織でできていて

この繊細な臓器は 硬い頭蓋骨と

Inside its protective membranes and the skull's hard casing,

内部の保護膜で しっかりと保護されています

this delicate organ is usually well-shielded.

But a sudden jolt can make the brain shift

それが急な衝撃で脳がずれ

and bump against the skull's hard interior,

頭蓋骨の内側にぶつかることがあります

and unlike jello, the brain's tissue isn't uniform.

ゼリーと違い 脳の組織は均一でなく

It's made of a vast network of 90 billion neurons,

900億ものニューロンの ネットワークで成り立っています

which relay signals through their long axons to communicate throughout the brain

長い軸索を伝って信号を脳中に伝達し

and control our bodies.

身体を制御しています

This spindly structure makes them very fragile

神経細胞は紡錘形のため 外力を受けやすく

so that when impacted, neurons will stretch and even tear.

衝撃が加わると 伸ばされたり 時には断裂します

That not only disrupts their ability to communicate

その結果 信号伝達が遮断されるだけでなく

but as destroyed axons begin to degenerate,

障害を受けた軸索が変性する過程で

they also release toxins causing the death of other neurons, too.

有害物質を放出し 他のニューロンを破壊することもあります

This combination of events causes a concussion.

このように複合した過程が 脳震盪の原因となります

The damage can manifest in many different ways

症状は多岐にわたり

including blackout,

意識喪失

headache,

頭痛

blurry vision,

視力低下

balance problems,

平衡機能の障害

altered mood and behavior,

気分や行動の変化

problems with memory, thinking, and sleeping,

記憶 思考 睡眠などの障害

and the onset of anxiety and depression.

不安やうつなどの精神障害などです

Every brain is different,

脳は人さまざま

which explains why people's experiences of concussions vary so widely.

だから脳震盪の症状もまちまちです

Luckily, the majority of concussions fully heal

幸いなことに ほとんどの場合は

数日から数週間で症状が消え完治します

and symptoms disappear within a matter of days or weeks.

Lots of rest and a gradual return to activity

脳が自然治癒する為には

allows the brain to heal itself.

十分に休息し 活動を暫く控えること

On the subject of rest,

休息と言えば

many people have heard that you're not supposed to sleep

脳震盪を受けた直後に眠ってしまうと

shortly after receiving a concussion because you might slip into a coma.

昏睡に陥る危険があると 聞いたことがあるでしょうか

That's a myth.

これはただの迷信

So long as doctors aren't concerned there may also be a more severe brain injury,

脳内出血などの 重い脳外傷が疑われる場合を除き

like a brain bleed,

寝てしまったことで問題が生じたケースは

there's no documented problem with going to sleep after a concussion.

報告されていません

Sometimes, victims of concussion can experience something

時に 脳震盪後遺症 (PCS)を

called post-concussion syndrome, or PCS.

発症する患者さんもいます

People with PCS may experience constant headaches,

症状には持続性頭痛

learning difficulties,

学習障害や

and behavioral symptoms that even affect their personal relationships

何か月 何年間も続く

for months or years after the injury.

人間関係を含む 行動の変化を示すこともあります

Trying to play through a concussion, even for only a few minutes,

脳震盪の直後に 数分でも無理にプレーを続けたり

or returning to sports too soon after a concussion,

焦ってスポーツに復帰することは

makes it more likely to develop PCS.

PCSの危険性を高めます

In some cases, a concussion can be hard to diagnose

症状が徐々に現れるために

because the symptoms unfold slowly over time.

脳震盪の診断が難しいこともあります

That's often true of subconcussive impacts

特に注意が必要なのは

脳震盪を引き起こさない

which result from lower impact jolts to the head

than those that cause concussions.

軽度の頭部への衝撃です

This category of injury doesn't cause noticable symptoms right away,

症状はすぐに現れないものの

but can lead to severe degenerative brain diseases over time

繰り返されれば いずれは

if it happens repeatedly.

重大な脳の変性疾患に繋がります

Take soccer players, who are known for repeatedly heading soccer balls.

例えば サッカーにつきもののヘディング

Using a technique called Diffusion Tensor Imaging,

拡散テンソル画像という技術で

we're beginning to find out what effect that has on the brain.

脳への影響が解明されてきています

This method allows scientists to find large axon bundles

この方法を使って 太い軸索の束を見つけ

and see how milder blows might alter them structurally.

軽度の衝撃による構造上の変化を調べます

In 2013, researchers using this technique discovered

この技術を用いた 2013年の報告によると

that athletes who had headed the ball most,

about 1,800 times a year,

年に最も多い回数（約1800回）

ヘディングをした選手には

had damaged the structural integrity of their axon bundles.

軸索の束に 構造上のダメージが認められました

The damage was similar to how a rope will fail

一本一本の線維が劣化すると

when the individual fibers start to fray.

縄自体がちぎれてしまうのと同じです

Those players also performed worse on short-term memory tests,

これらの選手たちは 短期記憶のテストの結果も悪く

so even though no one suffered full-blown concussions,

はっきりした脳震盪は 受けていないにも拘わらず

these subconcussive hits added up to measurable damage over time.

軽度の衝撃が積み重なることで 検査に現れる損傷に繋がったのです

研究によれば 過剰な数の 脳震盪に至らないまでの軽度な衝撃は

In fact, researchers know that an overload of subconcussive hits

is linked to a degenerative brain disease known as Chronic Traumatic Encephalopathy,

慢性外傷性脳症(CTE)と呼ばれる 進行性の脳変性に

関連付けられています

or CTE.

CTE患者は30-40代を境に

People with CTE suffer from changes in their mood and behavior

that begin appearing in their 30s or 40s

followed by problems with thinking and memory

気分や行動の変化に続き

思考や記憶の障害を発症します

that can, in some cases, even result in dementia.

痴呆症に発展することもあります

The culprit is a protein called tau.

犯人は タウというタンパク質です

Usually, tau proteins support tiny tubes inside our axons called microtubules.

普段は 軸索内の微小管を保護しています

It's thought that repeated subconcussive hits damage the microtubules,

脳への繰り返す衝撃で 微小管がダメージを受けると

causing the tau proteins to dislodge and clump together.

タウが遊離して凝集します

The clumps disrupt transport and communication along the neuron

それがニューロンの信号伝達を阻害し

and drive the breakdown of connections within the brain.

脳内信号伝達を障害します

Once the tau proteins start clumping together,

タウがいったん凝集し始めると

they cause more clumps to form

さらに凝集を加速し

and continue to spread throughout the brain,

脳への衝撃が止んだ後も

even after head impacts have stopped.

脳中に広がります

The data show that at least among football players,

アメフト選手に関しては 50-80%の脳震盪が

between 50 and 80% of concussions go unreported and untreated.

報告も治療も受けず 放置されているそうです

Sometimes that's because it's hard to tell

そもそも脳震盪が起こったのかどうか

a concussion has occurred in the first place.

But it's also often due to pressure or a desire to keep going

判断が難しい場合もあれば

異常に気付いていても プレーを続行したい しなければという

プレッシャーに負けることもあります

despite the fact that something's wrong.

これは回復を阻むだけでなく

This doesn't just undermine recovery.

It's also dangerous.

とても危険なことです

Our brains aren't invincible.

脳は不死身ではありません

They still need us to shield them from harm

まず衝撃を防ぐこと

and help them undo damage once it's been done.

また受けてしまった衝撃は きちんと手当することが重要です