In this video I briefly explain how information can be collected about the structure and function of a living brain using scanning and imaging techniques including EEG, CAT scan, PET scan, MRI, fMRI, and DTI.

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Video Transcript:

Hi, I’m Michael Corayer and this is Psych Exam Review and in this video I’m going to talk about some brain scanning and imaging techniques and these can be broadly divided up into structural techniques which reveal the structure of the brain or functional techniques; these are techniques that show us the actual brain activity in a living brain.

So we’ll start with the EGG this is actually one of the first scanning technologies and this stands for electroencephalograph. So the electro refers to electricity encephalo just means related to the brain and then we’re going to be creating a graph of these results. So the electroencephalograph looks at levels of electrical activity in the brain and graphs them. The way this is done is that the scalp is covered with electrodes stick electrodes all over the scalpe and each of these electrodes detects the activity underneath and then this is summed together and put into a graph.

So we can see the electrodes all over the scalp will give us something that looks a bit like this. Well not quite, similar though. Here’s an actual EEG picture here. Each of these electrodes is detecting electrical activity. When this is then graphed we get these waves of activity like this. These peaks and valleys, increases and decreases in the electrical activity and this is what we “brain waves”.

Now this isn’t a very specific imaging technique. So the function that we’re seeing is overall activity. We’re not able to see precise areas that are more or less active. We can see overall patterns, so we could look at an EEG and we could tell if somebody was awake or sleep or maybe what stage of sleep they’re in or whether they’re meditating.

So we can get some general patterns. We’ll see some examples of this when we talk about sleep in the future. An EEG was used to first identify the different stages of sleep that we go through.

OK so that’s the EEG. The next one that we’ll look at is the CAT scan or CT scan. This stands for computerized axial tomography. This is a structural technique, so this is just going to reveal the structure of the brain, it’s not going to actually show any activity that’s occurring. OK, so what is tomography first of all? You might be wondering.

Well tomography refers to the idea that we have some 3D object, let’s say this is an orange here, make this look sort of three dimensional here, so we have an orange here and what tomography is, is you slice the object. You take a slice of a 3D object and from that slice you can look at it in a 2D picture that reveals the structure.

So if I were to slice the orange this way and I looked at that bottom half I could now see the internal structure of that orange in this 2D picture. So that’s all that tomography means. We’re taking a 2D slice of a 3D object and that’s going to reveal the structure.

So what a CAT scan does is it does this with the brain using x-rays. So we send x-rays through at a number of different angles, so that’s where the axial refers to, send x-rays through different axes, and then that gives us these 2D pictures that reveal the structures. We can see the densities of different areas and from that we can figure out the structure.

So let’s see what these are going to look like. We get things like this, so we can see there’s different angles here of x-rays being sent through the brain or through the skull. We can see the different densities of different tissue and that tells us about the structure. We can see if there’s any abnormalities we might see if there’s damage to a certain brain area. We could look in and try to find a tumor or something, it would be a different density than the tissue around it so a CT scan would allow us to see that.

OK the next technique that we’ll look at is a PET scan. So we have a cat scan and a pet scan. This is a functional technique. This stands for positron emission T – tomography. So again we’re going to be looking at a 2D slice of a 3D object, in this case, the brain.

So the way that a PET scan works is that the person ingests a radioactive substance, so they take a pill or get an injection and this goes into the bloodstream and then it goes into the brain. So what we then do is we put them in the scanner and the scanner detects the levels of this radioactive substance and therefore we can tell how much blood activity there is in a certain area. We can see the blood flow to certain areas.

So what does this tell us about function? Well the areas of the brain that are more active are going to require more blood flow because they’re going to be using more energy. And so by seeing which areas have greater blood flow we can estimate which areas of the brain are more active. So then we color code this information and we put it into this graph and we see something like this.

So this is a PET scan and the blue areas are less active, the yellow and orange areas are more active they have more blood flow. That means those areas of the brain are using more energy, therefore they’re probably more active.

But as you can see from this picture, it’s not a very specific measure of brain activity. We get a general idea of regions that are more or less active.

Ok, let’s look at another structural technique. This one we’ll look at is the MRI. So MRI stands for magnetic resonance imaging. So the basic way that this works is that we send a magnetic pulse through the brain and what this does is it causes molecules to move slightly, twist and then relax, and then we can pick up on the energy that’s released from this movement.

And what that allows us to do is see that different areas of the brain, different structures are going to respond differently to this magnetic pulse and then we can figure out the structures based on this difference. So this is going to give us a more precise look at the structure of the brain.

So let’s see what an MRI is going to look like. Here we can see this is much more detailed than the CT scan we had earlier. So what happens, we send this pulse through the brain, different areas respond differently and then we use that information to create this detailed picture. That’s an MRI and that’s a structural technique.

But we can also use the MRI in a functional way. This is called an fMRI. It should be easy to remember that this is a functional technique because the f stands for functional. So this is a functional MRI.

The way that this works is almost the same as the MRI we had before where we send this magnetic pulse through but in the fMRI we’re looking at the response of molecules of hemoglobin, in the blood. So now we’re able to see different levels of blood flow in different areas of the brain. Just like we did with the PET scan, we can use that information to figure out which areas of the brain are more active.

So in this case we’re looking at the response of hemoglobin and this gives us an idea about brain activity. So let’s see what that would look like.

Ok so what we can do is we have someone in an fMRI scanner and we can actually have them do certain tasks. So we can put a screen in there, they can look at pictures, we can give them a button to press with their hand to answers questions. So we can do things like have them look at faces and we can see which areas of the brain are more or less active during this task. Then we can compare that to other objects, ok, they’re looking at houses. We can say some areas are the same activity or some areas are more or less active. We can figure out which areas of the brain are involved in something like facial recognition.

Again, you can see from these pictures this is more precise than we had with the PET scan in terms of specific areas but it’s not super-precise. We get a general idea of regions but we’re not looking at individual neurons firing or anything like that. OK so that’s fMRI.

I’ll end with one last scanning technique and this is one that you might not see in your textbook, this is a newer technique and this is DTI and this stands for Diffusion Tensor Imaging. So what diffusion tensor imaging does is it looks at the diffusion of water in the brain.

The idea is that water is going to be distributed throughout the brain but it’s going to diffuse differently in different areas. So for instance if I have a bundle of nerve fibers here, I have a bunch of axons here in this direction a tract, this bundle of nerve fibers, what’s going to happen is the way that water is going to be defused along these axons is going to be different than the way it’s diffused across them.

So the water is not going to be easily diffusing across the cell membranes but it’s going to move along the axon more easily. So that diffusion of water throughout the brain actually reveals the structures. So we can look and we see that, you know, the water is distributed in this particular way and that tells us that there’s probably a bundle of nerve fibers here. So we can then collect all this information, then color code it and make these stunning images like this, where, this is a DTI image, where what we see is because the diffusion of water was different in this direction vs. this direction that tells us there is a tract here of nerve fibers so this is called tractography and we can now see how these networks are spread out across the brain.

Again this is just a structural technique, we’re not actually seeing the activity of these areas. Ok, so that’s DTI, diffusion tensor imaging. OK so those are all of the brain scanning and imaging techniques that you should be familiar with I hope you find this helpful, if so, please like the video and subscribe to the channel for more.

Thanks for watching!