- [Voiceover] Today we have many different ways
of studying the brain and I want to go over a few
of them here.
And, in future videos we'll go into a lot more depth
about each of these methods, but I wanted to give you
a quick overview of all of them in order to show you
how they relate to one another.
And, I'm going to split them into two broad categories,
those that tell us about brain structure
and those that tell us about brain function.
And, on the structural side we'll start with CAT scans
or CT scans which stands for Computerized
Axial Tomography.
And, this method uses X-rays in order to create
an image of the brain.
And, this is super useful in that it can show us
whether or not someone has a tumor or if there's
abnormal swelling or bleeding.
But, it can't tell us anything about what areas of the brain
are active at a given time.
Another way that we can look inside of the skull
to look at brain structures is with Magnetic
Resonance Imaging, or MRI.
And, instead of using X-rays like a CAT scan
this method uses radio waves.
So, a person's head is placed within a machine
and they're exposed to a strong magnetic field.
And, this magnetic field causes the atoms in the brain
to line up, to align in a certain direction.
And, after this is setup a radio wave is added to that
magnetic field which disrupts the orientation of the atoms.
And, as the atoms move back to align with that original
magnetic field they emit a signal.
And, most importantly, different types of atoms
emit different signals and this allows for the creation
of a detailed picture of the brain,
much more detail than you would see with a CAT scan.
But, much like a CAT scan while the MRI can give us
a detailed image of the structure of the brain
it also doesn't tell us anything about brain function.
It can't tell us anything about what the brain
is actually doing.
And, to look at that we have to use different methodologies.
For example, researchers can use Electroencephalography
or EEG in order to measure the electrical activity
that is generated by neurons in the brain.
And, this is done by placing electrodes on someone's scalp
at predetermined positions, usually by using a cap
with electrodes that are filled with a conductive gel.
And, unlike single cells recordings these electrodes
are not invasive, they don't have needles or anything,
they're just placed right on the scalp.
But, because they are external to the brain,
because they're external to the cells
they can't really tell us anything about the activity
of individual neurons, or even groups of neurons.
Instead, they look at the sum total electrical fields
that are generated from the brain.
And, unlike structural methods like CAT scans and MRIs
we don't get a picture of the brain from an EEG.
Instead, we get these, these wavy lines here.
And, while they might look kind of random to you
this is actually really meaningful for someone
who knows how to read them.
For example, they can tell us whether or not a person
is a awake or asleep, or they can identify
if a person is having a seizure.
And, it can even tell us if people are engaged
in certain congnitive tasks.
Another type of functional recording is
Magnetoencephalography or MEG.
And, this records the magnetic fields that are produced
by the electrical currents in the brain.
And, I don't mean to give you too many acronyms
but these magnetic fields are measureed using
Superconductive Quantum Interface Devices,
which are also know as SQUIDs.
And, this technique has a better resolution than EEG,
but it is also a lot more rare, at least within
the social sciences.
Possibly because it requires a large machine
and you need special shielding for the room
that it's placed in.
By comparison, EEG requires a lot less of a set up,
and you don't need a special room for it.
So, we have structural imaging here,
and functional imaging here,
and one thing you might be thinking is
wouldn't it be great if we could combine them?
And, we can and the most popular and well known
of these combined methods is FMRI
which stands for Functional Magnetic Resonance Imaging.
So, in this case we have the same structural image
from the MRI but we can also look at which of these
structures are active.
And, the idea behind this is that neurons that are firing
a lot, so neurons that are working hard at any given moment,
require more oxygen than neurons that aren't really active.
And so, by measuring the relative amounts of oxygenated
to deoxygenated blood in the brain we can get an idea
of what parts of the brain are active,
of what parts of the brain we're using to do a certain task.
So, there might not be a lot of activity in
the visual cortex when someone has their eyes closed,
but when their eyes are open that area of the brain
would light up on the FMRI.
The next type of methodology that is both
structural and functional is Positron Emission Tomography
or PET scans.
And, while on their own they can't really give us
a super detailed structural image of the brain
we can actually combine them with the
structural technology that we talked about
earlier like CAT scans and MRIs.
And, to do this technique a kind of radioactive
glucose is injected into a person.
And, since active cells naturally use more glucose
because they're using up the most energy and need to
replenish it, we can directly see what areas of the brain
are more active at a given point in time.
But, even so FMRI is a lot more popular,
at least within the social sciences.
And, this is probably because PET scans are a lot
more invasive, you actually need to inject someone
with a substance.
And, like I said, in future videos we'll go back
and discuss each of these techniques in a lot more detail.
But, hopefully this gives you a good idea
of how each of these different methods work
and what they can be used to study.