Functional Magnetic Resonance Imaging (fMRI)
Doctor Johan Jansma demonstrates functional magnetic resonance imaging (fMRI), a key neuroimaging technique.
So what we do here is fMRI. The â€˜fâ€™ stands for functional and it means that we take a picture of the activity of the brain. We actually make hundreds of pictures in a couple of minutes, and when we put them together we can see the activity of the brain during that period. We use an MRI scanner; it is a magnetic resonance imaging scanner. It is a large magnet that creates the field so we can measure the signal. We set the scanner so that we are sensitive to the signal changes related to the blood flow in the brain. The blood flow in the brain is actually related very precisely to the activity in the brain. When a region becomes active, there is an increase in blood flow. Itâ€™s a very safe technique; it doesnâ€™t use any radioactive signals. Its also non-invasive thereâ€™s no preparation needed. The only thing that is very remarkable about making an fMRI scan is that there is a lot of noise. In the background you can hear the noise of the pump. Also, when the scanner goes on thereâ€™s a very loud noise and those are the gradients â€“ the actual magnets that go on and off. We are here to do a task in the scanner that will focus on faces and houses. The idea is that faces, when they are presented on top of a house, they may distract you. The task that weâ€™re doing shows two houses, and the subject has to tell me if the houses are the same. On top of the houses is sometimes a face: a happy-looking face or a sad-looking face. Whenever the houses are the same press one button and if theyâ€™re different they push another button. In healthy people, we do not expect a lot of difference between the faces being sad and happy but in patients with depression we expect sad faces to show much more activity. and to make it more difficult to do the task. Now we are going to put the person in the scanner and he will do this task and we can look at the activity. Okay John, everything okay? Just perfect Here comes the first scan of about half a minute â€“ a test scan. We can see the subject in the scanner, and we can see the screen, the task and his responses. This is the noise; we can turn it down here. This first scan we make to get an idea of where the head is so that we can use that to â€¦ choose the other regions we want to scan. This is the real scan Iâ€™m going to make â€“ the functional scan. I can choose the region I want to scan of his brain. Iâ€™m going to have the amygdala in the middle, so Iâ€™m going to go a little low. Iâ€™m missing the top of his head, but Iâ€™m not interested in that right now. Iâ€™m going to change the number of scans I want to make, Iâ€™m going to make 200. Iâ€™m going to make 200 scans and every scan is about two seconds. I can push scan and my task will automatically start when the scan is running. Okay John, Iâ€™m going to start the scan. It will be about five minutes. Okay When I start the scanner then the task starts at the same moment. And now we just wait five minutes. You can see actually the scans coming up real time here, but you cannot see any activity in the scan because thatâ€™s only a statistical measurement. So here are the same pictures. And here I can actually see what is exactly on the screen that he would see. It should be exactly the same. This is good. So here we have results of a subject that did this task. What you see is activity in the visual cortex, lower in the brain (this is the Tailerach coorinates) and higher in the brain. This is the front of the head, the eyes, and this is the back of the head. The visual cortex processes visual stimuli so you expect it to be active. We also see that it is a little bit more active for the sad faces on the houses and also a little bit more for the happy faces on the houses. But there is very little differences between the sad faces and the happy faces and that is what I expected from healthy people in this task.
fmri, mri, functional, magnetic, resonance, imaging, imagery, scan, scnner, neuroimaging, blood, flow, magnet, johan, jansma
- ID: 2276
- Source: DNALC.G2C
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