There are many types of non-invasive BCI, and there is also a lot of research done using non-invasive BCIs. Because after all, it is less likely to cause harm to the human body, there are fewer legal issues.
I will introduce them one by one in the following posts. The first one I would like to introduce is functional magnetic resonance imaging (fMRI).
Everyone may have heard of MRI in hospitals, but what is fMRI?
What’s the difference between the two? let’s see
How does MRI work?
I will try to keep it simple since this is not the main point of this article. When you apply a magnetic field, the atoms will be arranged to rotate along the magnetic field. Then you will use radiation to knock the aligned atoms out of their original rotation direction. When they rotate back because of the always-on magnetic field, it will release radiation. The machine is able to create images based on the radiation emitted from those atoms. Simple, right? The picture below gives you a clear image of what happens during an MRI
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An MRI machine looks like this
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The circular part is actually an electromagnet that rotates and moves along the subject’s head. The images will be created “slice by slice” once the machine finishes scanning. We then stack the pictures to understand the structure of the brain. Of course, it doesn’t actually slice your head, it only detects the radiation emitted from your brain. This method can also apply to other body parts to see if there are any abnormal tissues inside your body, but I’m not a doctor, so for the detail, please consult someone with more medical knowledge.
How does fMRI work?
A little history about fMRI. There is a Japanese scientist called Seiji Ogawa who discovered something really interesting. Oxygenated blood has different properties under magnetic fields than deoxygenated blood. In case you don’t know, it consumes energy when the brain is processing the information. The blood is what provides energy and oxygen to the enormous amount of cells inside the brain. You probably wouldn’t feel it, but for example, when you talk, there will be an increased amount of blood flow into the area of language processing in order to provide nutrients and oxygen to it. There will be a delay for this reaction of about 1-5 seconds, but wow such a coincidence. We can use the information about oxygenated blood to stack on the structure that MRI creates originally, so then we know which part of the brain is working while subjects do some specific tasks. That’s the basics of fMRI, for more detail about the procedures you can read the article here.
The image that fMRI creates will look like this:
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The red and some yellowish parts in the image indicate the area where oxygenated blood presents, which are also the areas that are functioning.
Methods
Subjects will be asked to perform certain tasks as simple as listening to some beep sounds to some psychological tasks (I will introduce them in later posts). The machine would locate the head and start scanning while subjects are performing the tasks. The process will take around 1 hour depending on the distance between the image slices.
Advantages of using fMRI
This is the most precise and accurate way so far for noninvasive BCI imaging. Compare to the other methods of noninvasive BCI that I introduce, you will know how precise fMRI is in terms of knowing the functioning area of the brain
Disadvantages of using fMRI
Super slow, there are many different sayings about the duration of fMRI, but most of them are more than 30 mins. Think about it, if you tried to control a machine with your brain and it starts moving after 30 mins, you may as well just use other methods.
Super expensive, it is really precise, things are going to be expensive when it reaches this level. People would not be able to have one in their house
Not convenient, when the machine is scanning, the subject cannot move, otherwise, the image will be affected.
Not a real-time message. As I said in the previous paragraph, fMRI measures blood flow, not neural activities which are going to have a delay. Also, the magnitude may not directly reflect the strength of neural activation, because it might not be linear since the blood vessels distribute differently across the brain.
My Opinions
Based on the things above, fMRI is mostly used in the research or medical area. For example, if you want to know precisely which areas of the brain are going to be activated when people move their arms, we use fMRI first and use other noninvasive methods to detect the same areas in real-time to have a real-time BCI
So why should we know about this noninvasive method? Because it is very precise. In BCI we always meet a lot of trade-offs. You either sacrifice the preciseness or you sacrifice real-time detection. If you want both of them, then you have to sacrifice the non-invasive part. fMRI is the method that preserves the maximum preciseness while keeping it non-invasive.
We will end the introduction of fMRI here, if you have any questions, you are welcome to leave a comment!
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