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Each year in the United States,
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players of sports
and recreational activities
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receive between 2.5
and 4 million concussions.
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How dangerous are all those concussions?
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The answer is complicated,
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and lies in how the brain responds
when something strikes it.
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The brain is made of soft fatty tissue,
with a consistency something like jello.
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Inside its protective membranes
and the skull's hard casing,
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this delicate organ
is usually well-shielded.
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But a sudden jolt can make the brain shift
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and bump against
the skull's hard interior,
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and unlike jello, the brain's tissue
isn't uniform.
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It's made of a vast network
of 90 billion neurons,
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which relay signals through their long
axons to communicate throughout the brain
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and control our bodies.
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This spindly structure makes
them very fragile
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so that when impacted, neurons
will stretch and even tear.
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That not only disrupts their ability
to communicate
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but as destroyed axons begin
to degenerate,
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they also release toxins
causing the death of other neurons, too.
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This combination of events causes
a concussion.
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The damage can manifest
in many different ways
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including blackout,
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headache,
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blurry vision,
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balance problems,
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altered mood and behavior,
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problems with memory,
thinking, and sleeping,
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and the onset of anxiety and depression.
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Every brain is different,
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which explains why people's experiences
of concussions vary so widely.
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Luckily, the majority of concussions
fully heal
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and symptoms disappear
within a matter of days or weeks.
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Lots of rest and a gradual return
to activity
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allows the brain to heal itself.
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On the subject of rest,
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many people have heard that
you're not supposed to sleep
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shortly after receiving a concussion
because you might slip into a coma.
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That's a myth.
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So long as doctors aren't concerned there
may also be a more severe brain injury,
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like a brain bleed,
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there's no documented problem with
going to sleep after a concussion.
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Sometimes, victims of concussion can
experience something
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called post-concussion syndrome, or PCS.
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People with PCS may experience
constant headaches,
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learning difficulties,
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and behavioral symptoms that even
affect their personal relationships
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for months or years after the injury.
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Trying to play through a concussion,
even for only a few minutes,
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or returning to sports too soon
after a concussion,
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makes it more likely to develop PCS.
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In some cases, a concussion
can be hard to diagnose
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because the symptoms unfold slowly
over time.
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That's often true of
subconcussive impacts
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which result from lower impact jolts
to the head
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than those that cause concussions.
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This category of injury doesn't cause
noticable symptoms right away,
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but can lead to severe degenerative
brain diseases over time
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if it happens repeatedly.
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Take soccer players, who are known
for repeatedly heading soccer balls.
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Using a technique called
Diffusion Tensor Imaging,
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we're beginning to find out what effect
that has on the brain.
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This method allows scientists to find
large axon bundles
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and see how milder blows
might alter them structurally.
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In 2013, researchers using
this technique discovered
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that athletes who had
headed the ball most,
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about 1,800 times a year,
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had damaged the structural integrity
of their axon bundles.
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The damage was similar to how
a rope will fail
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when the individual fibers start to fray.
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Those players also performed worse
on short-term memory tests,
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so even though no one suffered
full-blown concussions,
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these subconcussive hits added up
to measurable damage over time.
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In fact, researchers know that an
overload of subconcussive hits
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is linked to a degenerative brain disease
known as Chronic Traumatic Encephalopathy,
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or CTE.
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People with CTE suffer from changes
in their mood and behavior
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that begin appearing in their 30s or 40s
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followed by problems with thinking
and memory
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that can, in some cases, even result
in dementia.
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The culprit is a protein called tau.
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Usually, tau proteins support tiny tubes
inside our axons called microtubules.
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It's thought that repeated subconcussive
hits damage the microtubules,
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causing the tau proteins to dislodge
and clump together.
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The clumps disrupt transport
and communication along the neuron
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and drive the breakdown of connections
within the brain.
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Once the tau proteins
start clumping together,
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they cause more clumps to form
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and continue to spread
throughout the brain,
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even after head impacts have stopped.
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The data show that at least
among football players,
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between 50 and 80% of concussions
go unreported and untreated.
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Sometimes that's because it's hard to tell
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a concussion has occurred
in the first place.
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But it's also often due to pressure
or a desire to keep going
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despite the fact that something's wrong.
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This doesn't just undermine recovery.
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It's also dangerous.
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Our brains aren't invincible.
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They still need us to shield
them from harm
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and help them undo damage
once it's been done.