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And how to try to describe it to them.
I found, over time, it's really difficult for people
to understand it.
It's just very complicated with this tiredness, the cataplexy,
the fragmented sleep at night.
If you're a normal person, you've got sleep,
and you've got your waking life.
And occasionally, they'll overlap a little bit.
For me, I live in this world that
is, very rarely am I fully awake, and very rarely am I
fully asleep.
I live in the in-between.
I'm Tom Scammell.
I'm a professor of neurology at Harvard Medical School.
Narcolepsy is a neurologic disorder.
It is one of the most common sleep disorders
and affects about 1 in 2,000 people.
It doesn't matter how much sleep they get at night.
They're going to sleep every day.
People also can have a variety of other symptoms.
These include hypnagogic hallucinations,
where they could have very vivid dreamlike hallucinations just
as they're drifting off to sleep or just when they awaken.
They could have something called sleep paralysis, where,
as they're falling asleep or sometimes when they wake up,
they can't move.
And then there's cataplexy, which
is similar to sleep paralysis.
The distinction is that cataplexy occurs right
in the middle of the day and is triggered by strong emotions.
And then the last thing, which is perhaps
in sort of one of the strangest of all,
is that, for considering that somebody with narcolepsy
is often very sleepy through the day,
they often have fragmented sleep at night.
They could wake up four or five times for 10 or 20
minutes for no clear reason.
And so in the same way that they have trouble maintaining
wakefulness through the day, they
can have trouble maintaining sleep through the night.
Somewhere between age 10 and age 20 or so
is when narcolepsy begins.
People usually start off with sleepiness,
and then the other symptoms follow.
So there's a number of different systems
in the brain that are involved in promoting arousal
or wakefulness and sleep.
Up here's the cortex.
This is the front, near the forehead.
Here's the back.
This is the brain stem coming down here.
And this is the cerebellum, which was involved in balance.
The brain stem is the site that most
of these arousal-promoting signals come from.
And those cells send connections up
throughout the whole front part of the brain,
and they help turn on the cortex and other parts of the brain
when you're awake.
There's also some cells in a small region
called the hypothalamus that are involved in promoting sleep.
And these sleep-promoting cells, one of the things they do
is they actually turn off the wake-promoting cells.
And so that allows you to be fully asleep without any hint
of consciousness.
This is called the mammillary body.
And just about it right here, is where the hypocretin neurons
sit.
And this is a really critical collection
of neurons, brain cells, that makes very particular
and special neurotransmitters known as hypocretin, or orexin.
Those are just two names for the same thing.
The hypocretin-producing cells help
activate and sustain activity in the other wake-promoting brain
regions across the day.
The brain contains billions of neurons.
And only a very, very small number of these
produce hypocretin.
It's probably somewhere between 100,000 and 200,000,
which sounds like a large number.
But when you compare it to 10 billion neurons,
it's really very small.
In narcolepsy, those hypocretin-producing producing
cells die off.
When you look closely at the brain of somebody who
has narcolepsy, what you see is about a 90% to 95%
loss of the hypocretin-producing neurons.
So there's two broad themes that are being pursued in narcolepsy
research right now.
One theme is to understand what goes wrong in the brain
when the hypocretin-producing cells die off.
How does that lead to sleepiness and
cataplexy and other symptoms?
Another big theme is trying to understand what actually kills
the hypocretin neurons in the first place,
because if we could understand that, then it's possible
that one could diagnose and recognize narcolepsy
right at the earliest stages.
We might be able to get in and stop that process.
As we've discovered more and more
about what's actually causing the hypocretin neurons to die
off, and as we've discovered more about the consequences
of that for the brain, it's really
given us a lot of hope for new opportunities for coming up
with better therapies for people with narcolepsy.
If we could get hypocretin back in the brain somehow,
that would be potentially as great as giving insulin
to people with diabetes.
It would really be the missing factor coming back into play.
And it could, in theory, cure their sleepiness
and cure their cataplexy in the most thorough fashion.
Right now, scientists are working
with a variety of techniques to try to get hypocretin signaling
back into the brain.
But the hope is that in 5, 10, or 15 years,
we may see those hypocretin replacement therapies coming
into clinical practice.