- [Voiceover] Let's say you're a clinician
and you want to tell if someone has multiple sclerosis.
One of the first things you might do
is you might actually look into their brain.
The way to do this is to use a technique
called Magnetic Resonance Imaging,
otherwise known as MRI.
What you do is you have someone lay down on this bed
and they enter this kind of cramped and really loud
machine over here.
That machine is actually gonna take pictures of their brain.
Interestingly enough, it's actually gonna take pictures
from three different perspectives.
On the left, we kinda have a picture of someone
who looks like they're looking towards the left.
This slice of the brain is called a sagittal slice.
In the middle, it looks like we have a slice
of someone who's looking in this direction.
So it's kinda as if we're looking
down from the top of their head.
We call this a horizontal slice.
On the far right, we have a slice of someone
who looks as though they're looking towards or away from me.
We call this a coronal slice.
In all three slices you'll see one thing that's common.
They have this bright spots over here.
These bright spots that they actually point out.
These bright spots are referred to as lesions.
A lesion is just a piece of damaged tissue.
If you think someone has multiple sclerosis
and you have all these brain scans,
the first thing you're gonna look for
are these bright spots here.
These bright spots are actually located
wherever there is a white matter.
Remember that the white matter is really just the
axons and the myelin of your neurons.
So this informative, right?
You see that you have damage in the brain,
but that damage could result from anything.
So we haven't really narrowed down specifically.
We can still do a few more tests
to really confirm that this is multiple sclerosis.
We can actually do something
that is a little bit more invasive.
Here I have a picture of someone's lower back.
In purple here is the person's spinal cord.
You can see this kind of blue stuff
that's surrounding the spinal cord
and that stuff is just called your cerebrospinal fluid.
The cerebrospinal fluid just bathes
both the spine and your brain.
It contains all sorts of good things;
proteins and ions and all sorts of things that you need
for the brain and spinal cord to work.
What we can do is we can actually extract
that cerebrospinal fluid using this needle,
and we can collect it into this vial.
Now we have a vial
and that vial has a whole bunch of cerebrospinal fluid,
but the question is, what is in that cerebrospinal fluid?
There's going to be something in here
that's characteristic of multiple sclerosis.
What is that thing?
Remember that multiple sclerosis is an autoimmune disease
so the immune system is really crossing paths
with the nervous system.
We want to see something that's characteristic
of the immune system.
So maybe if we kinda zoom in here.
What's characteristic of the immune system?
Well, antibodies.
If you have a lot of antibodies in your cerebrospinal fluid
then that may indicate that your immune system
is in the central nervous system.
How do we determine if there are antibodies in here?
We can use a technique known as
gel electrophoresis.
I'll spare you the details of how
exactly this technique works.
But really what it does is
first it separates the contents in your sample
and it allows us to visualize those contents.
Basically, we're gonna send this vial off to a lab
and they're going to perform gel electrophoresis.
When you separate the contents of this
cerebrospinal fluid and when you visualize it,
it looks something like this.
Here, I kinda have two different strips for you.
The left strip corresponds to a person who is healthy.
The right strip corresponds to someone who has
multiple sclerosis.
Immediately, you'll notice that there are these
white bands over here.
These bands, they're gonna correspond to different proteins.
In the healthy sample, you'll notice that these bands
are separated uniformly.
But in the multiple sclerosis sample,
you'll see that there are these thicker bands over here.
These thicker bands are referred to as
oligoclonal bands.
When you see these oligoclonal bands,
that's actually pretty indicative that there are
a lot of antibodies in this sample.
Because you have a lot of antibodies in this sample,
that means you have a lot of antibodies
in your cerebrospinal fluid.
That tells us that the immune system is really really active
in the central nervous system.
So we have two pieces of evidence.
We have pictures of the brain that showed the lesion
and we have evidence that shows
that the immune system is involved
in the central nervous system.
But there's still one more test that we can do
to definitively say that this person has multiple sclerosis.
We can actually measure the electrical activity
in the person's brain.
Let's say you have a person here
and he's just sitting in a dark room,
and you put these electrodes here onto their scalp.
Those electrodes are gonna measure their brain activity.
More specifically, it's gonna measure the brain's response
to some kind of visual stimulus.
In this case, it's a computer screen.
On your computer screen, you have a checker board.
You have all these black tiles
and you have all these white tiles.
These tiles are actually going to alternate
every half second or so.
So maybe every half second so, all the black tiles
are now in pure white, and all the white tiles
will now be pure black.
It's just gonna alternate back and forth.
We're basically measuring the brain's response
to this visual stimulus.
That response is gonna be called a
visual evoked potential.
What are we measuring here?
Well, we're measuring an electrical response.
We're gonna measure it graphically.
Let's say we have a graph over here.
On the x-axis is time, usually on the scale of milliseconds.
And on the y-axis, we have voltage,
usually on the scale of microvolts.
Let's say we're kinda measuring the person's brain activity
and at some point the checker board alternates,
and we're gonna see this kind of peak in the voltage.
It's gonna go back down and continue onwards.
We're gonna be looking at these peaks
in response to the alternating checker board.
Usually, you collect data from a lot of peaks,
but this is just one such example.
Now, given that this is a visual evoked potential,
you're gonna be measuring activity
from visual areas in the brain.
Let's say you have your eyes over here,
so this is the person's eyes.
At the back of the eyes are the optic nerves.
The optic nerves will carry visual information
in the form of electrical activity to the rest of the brain.
Let's just say for the sake of argument
that this person has a lesion in their left optic nerve.
The right optic nerve, however, is perfectly healthy.
So when we measure the electrical activity
from both of the optic nerves, we can actually compare them.
We can compare activity from the healthy optic nerve
to activity from the damaged optic nerve.
Let's say that the graph that I've drawn here,
as it is now, is just the optic nerve that's healthy,
so it's the right optic nerve.
Then you look at the electrical activity
from the left optic nerve,
it might look like something like this.
Immediately, you could tell that there's actually
a delay between the two.
It took a longer period of time for the left optic nerve
to respond to the alternating checker board.
This actually makes a lot of sense
because if we think back to it,
let's say we have a neuron over here,
ordinarily your neurons have a bunch of myelin
that insulate their axons
and this myelin helps the electrical signals
travel then a lot more quickly on the axon.
But in multiple sclerosis, that myelin gets degraded.
When that myelin is degraded,
the signal that moves down the axon is a lot slower,
so when you have all these degraded myelin
over here on the left optic nerve,
it makes a lot of sense for the signal
to be slightly delayed.
I wanna make it clear that these signals
that I've drawn here aren't actually action potentials.
They're signals that you get from the overall nerve.
But in general, the principle is still the same.
You see there's a delay in the response.
So the left optic nerve is now slower
than the right optic nerve
because you have this lesion over here.
So all in all, I've shown you three very common tests
that people use when diagnosing multiple sclerosis.