Dra. Clarissa Cavarsan

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What are the differences among EEG, MRI and fMRI?

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There are several technologies developed to help neuroscientists understand human consciousness and behavior. Among these new technologies, we can highlight the ones that image the brain, like electroencephalography (EEG), Magnetic Resonance Imaging (MRI), and functional MRI (fMRI). What do those techniques consist? What are the differences among them? Take a look at the information we have here!

EEG: Electroencephalography, the beginnings of Neuroscience

The EEG history starts in 1875 when Richard Caton published on British Medical Journal his discoveries about electrical properties studying rats and monkeys’ brains. In the following decades some other great names as Adolf Beck, Vladimir Vladimirovich Pravdich-Neminsky, Napoleon Cybulski, Jelenska-Macieszyna and Hans Berger appeared. Hans Berger, in 1924, did the first EEG in humans. He created the first EEG, such a revolutionized tool for Neurology. This technique is widely used to diagnose epilepsy.

EEG-fMRI

How does EEG work?

To perform the EEG electrodes placed all over the head are able to measure changes in the electrical activities of the brain. Then, it is possible to register how the brain answer to different stimuli. This type of measurement is possible because the brain function is based on neurons network, that communicates through electrical and chemical signals. So, the more neurons activity, the more electrical activity, and the more brain activity.

An important detail is that EEG is not able to measure an isolated single neuron. EEG can measure the sum of the potential difference of several, millions of neurons together. Thereby, signals captured through electrodes are sent to an amplifier that sends the information to a computer. This last one can process the data and generate several images and data analysis.

To better understand how this technology works, we recommend this EEG-fMRI Webinar Course.

EEG-fMRI Webinar Course
In the vídeo you will find a Workshop of Brain Support Corporation, when Paulo Bazán explains how EEG works.

And how about MRI?

MRI is used to get an image from the entire body. For the brain, it gives a map that can be useful to compare brain areas among people, as studying healthy subjects compared to people with some disease.

MRI is a very complex technique. They generate a powerful magnetic field that interacts with protons of Hydrogen (H+) from our bodies. Our body is full of Hydrogen, as in water molecules or from hydrocarbons. As 70% of our body is water, we can say that we have a lot of hydrogens atoms that might be affected by the magnetic field and contribute to the information to generate the image.

The magnetic field, generated through MRI machines, can align protons, like this, they are not random distributes anymore. Then, a pulse is emitted, which can also Interact with protons, spinning them. As the pulse is very fast, right after the pulse, protons return to their initial aligned position. When they are returning, they release energy that is detected by sensors at MRI machine. The energy generates measured numbers data, and based on the different characteristics of each tissue, we are going to have a different amounts of energy been released. The data measured from the energy released is processed and based on that generate image showing the distribution of each tissue. Do you still have any questions? Institute of Biomedical Imaging and Bioengineering (NIBIB) brings more detailed information in How Does an MRI Scan Work?, of a series of Science videos.

Now you could wonder, how about fMRI?

fMRI: a step beyond Neuroimaging

MRI is able to generate an image in a specific moment. It means that it is not able to show differences according to some activity in response to some stimuli or different conditions. fMRI was developed to allow not static images from the brain. Images of a determinate duration of time.

In fMRI is also used the energy released from protons to get data to construct images. The difference is that the data is generated from Oxygen from blood flow. Thus, more activated areas are going to have more blood flow than less activated areas. This type of response is known as Blood-Oxygenation Level-Dependent response (BOLD). Looking for the blood flow implies a disadvantage of this technique because blood flow takes some seconds to change from one area to the other. To avoid false-negative data, we must run the response to stimulus in a series of repetitive trials, to get the answers (increased blood flow in areas activated).

How is it possible to compare all of these techniques?

As we demonstrated here, all three techniques are very different among them. So, we must know which of them is correct to be used to answer your scientific question. Besides that, we must consider the costs and laboratory structures.

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Autor: BrainSupport

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