How do psychologists see inside your head?
I remember the first time I ever held a human brain though its previous owner was no longer
with us to share in the experience So how do psychologists and neuroscientists look inside
the brain the centre of human existence without having to open up the skull?
The answer lies in a number of extremely clever scanning technologies, which uncover
some of the brain s mysteries without having to go anywhere near a drill or a saw. In fact,
brain scans are so incredibly clever that beyond the noise of the machine
you wouldn t even know your brain was being spied on.
Generally speaking, brain scans are used for one of two purposes: to uncover information
about the structure of a patient s brain (perhaps locating an area affected by a stroke or lesion),
or alternatively the scan might attempt to explore the function of a patient s
brain (which area of the brain activates under particular conditions?). Structure and function.
Let s take a look at four main types of brain scanning technology to understand
more about their usage, how they work, and why it makes sense to use one type
of scan instead of another, depending on the situation.
First, we ll look at two structural brain scans. These are scans that can tell you what a person
s brain looks like without having to remove it from the patient s head. Very convenient!
Computerised Tomography shortened to CT is an X-Ray-based scan,
which presents the neuroscientist with a picture that looks like a horizontal slice of the brain.
The word tomography worth remembering, because it comes up again comes from the Greek work TOMOS,
meaning cut, and that is very literally what a CT scan shows a picture of a cut across the brain.
Computerised because it is the magic of a computer that turns
multiple X-Ray beams into one clear picture. A second, common, for of structural brain scan
is Magnetic Resonance Imaging, or MRI. Unlike Computerise Tomography scans,
which beam X-Rays through the head, MRI scans construct their image of the brain
by passing a magnetic field over the head. Hydrogen molecules in the brain react to this
magnetic field by reverberating sending a wave back, which is recorded by the scanner
and then turned into an image of the individual s brain. MRI scans, incidentally,
are able to provide a much more accurate picture than CT scans do with their X-Ray technology.
And Magnetic Resonance Imaging can be used for more than just structural snapshots too.
If you ve ever seen a little f suck in front of MRI and wondered what the difference is,
then listen up! That f stands for functional: functional Magnetic Resonance Imaging.
Same technique as before, except, this time, multiple scans are taken as a patient is tasked
with completing a task. By taking multiple scans, neuroscientists are able to watch which areas of
the brain are activated in fulfilling the function under examination, in addition
to seeing the over structure of the brain. And to balance the structural-functional table,
let s look at one other example of a functional brain scan and this one,
unlike all of the other scans we ve discussed in this video, is an invasive technique.
The scan is called Positron Emission Tomography it s that Greek cutting word again!
PET scans are used less often than fMRI scans nowadays as it can t be used on
children or pre-menopausal women because it s radioactive. Radioactive! It s what?!
So, you know I said Positron Emission Tomography scans are invasive what I meant by this is that
these scans involve injecting the patient with a radioactive substance. Amazingly,
as crazy as this sounds, it s perfectly safe at the levels used, but as I ve already mentions,
this approach isn t for everyone. So, how does it work? The radioactive
substance is actually a form of glucose, which is injected into the patient s arm and travels
through the blood stream to the brain. Depending on the exact chemical chosen, the radioactive
glucose substance will accumulate in different parts of the brain. Typically, an active part
of the brain, because it s a part of the brain that is drawing oxygenised blood towards it.
As the substance injected into the blood stream is radioactive,
it releases positrons, so the scanner is recording areas of positron emission
it s sort of in the name and highlighting these areas as areas of functional activity
by producing a multi-coloured image of the brain that looks something like a heat map.
None of these machines are cheap a single machine costs upwards of a million dollars and that s
before we consider the operating costs, training and maintenance. But there s no doubt that these
ingenious machines, which turn our skulls into metaphorical fishbowls for neuroscientists to
gaze enquiringly within, have led to magnificent advancements in neuroscience and the discovery
of the neural basis of key human functions such as language, perception and memory.