Magnetoencephalography: what is it and what is it for

Magnetoencephalography is one of the best known and most widely used neuroimaging techniques in clinical intervention programs and research lines on the human brain. That’s why it’s an example of how technology helps us get to know ourselves better.

In this article we will see what it is and how the magnetoencephalography works, and what are their uses.

    Understanding the brain thanks to new technologies

    There is no doubt that the brain is a system made up of millions of extremely complex biological processes, including language, perception, cognition and motor control. This is why, for thousands of years, this organ has aroused great interest on the part of all kinds of scientists who have formulated various hypotheses about its functions.

    A few years ago, behavioral measurement techniques were used to measure cognitive processes; such as reaction time measurements and pencil-and-paper tests. Subsequently, throughout the 1990s, great technological advances made it possible to record the brain activities linked to these cognitive processes. This was a major qualitative leap in this field of research and a complement to the traditional techniques still used today.

    Thanks to these advances, we now know that a the functioning of the brain involves billions of interconnected neurons, forming what are called synaptic connections, and these connections are set in motion by electrical impulses in the brain.

    We can say that each neuron functions as if it were a “small electrochemical pump” containing ions charged with electricity and in continuous movement, both inside and outside the cell membrane. of the neuron. When neurons are charged, they provide a flow of current to cells, which in turn are stimulated; causing what is called an action potential which causes the neuron to trigger the flow of charged ions.

    This electrical potential moves to reach the presynaptic region, then releases neurotransmitters into the synaptic space that access the postsynaptic membrane of the cell and immediately cause changes in intra- and extracellular ion flow.

    As several synaptically interconnected neurons and cells are activated simultaneously, they provide an electric current accompanied by a magnetic field and, as a result, they flow into the cerebral cortex.

    It is estimated that to generate a magnetic field, measurable using measuring instruments placed on the head, 50,000 or more neurons must be active and interconnected. If the electric currents were to move in opposite directions, the magnetic fields accompanying each current would cancel out (Hari and Salmelin, 2012; Zhang et al., 2014).

    These complex processes can be visualized using neuroimaging techniques, one of which we want to highlight and which we will discuss in more detail in this article, magnetoencephalography.

      What is magnetoencephalography?

      Magnetoencephalography (MEG) is a neuroimaging technique used to measure magnetic fields produced by electrical currents in the brain. These electrical currents are produced by neural connections that exist throughout the brain to produce multiple functions. Each function produces certain brain waves and this would allow us to detect, for example, whether a person is awake or asleep.

      MAG, on the other hand, is a non-invasive medical test; therefore, when handling it, it is not necessary to introduce an instrument into the skull to detect the interneuronal electrical signals. This tool allows you to study the human brain ‘in vivo’, so we can detect various mechanisms in the fully functioning brain while the person is receiving certain stimuli or performing an activity. At the same time, it makes it possible to locate any anomaly if there is any (Del Abril, 2009).

      With the MEG, we can visualize three-dimensional moving images with which we can accurately detect, in addition to anomalies, their structure and the function they perform. This allows professionals to research whether there is a relationship with the personality of subjects with these abnormalities, to study whether genetics play a relevant role, and even to compare whether they influence cognition and emotions.

        Who is responsible and where is the MEG typically used?

        The specialist professional who is responsible for performing these brain assessment tests is the radiologist.

        This test, along with other neuroimaging techniques, is typically performed in hospital settings where all the necessary machinery is available.

        The systems that perform the MEG are carried out in a specialized chamber which must be protected in order to avoid interference that could occur through the strong magnetic signals that would produce the environment if it were carried out in any place. .

        To perform this test the patient is accommodated seated and a helmet containing magnetic sensors is placed on his head. The signals which provide the MEG measurement are detected by means of a computer.

        Other techniques to study the brain “in vivo”

        It is the techniques of neuroimaging, also called neuroradiology tests, that make it possible to obtain a picture of the fully functioning brain structure. These techniques they make it possible to study the disorders or abnormalities of the central nervous system in order to find a treatment.

        According to De l’Abril et al. (2009) The techniques most used in recent years, apart from magnetoencephalography, are as follows.

        1. Computed tomography (CT)

        This technique is used by a computer connected to an X-ray machine. The goal is to capture a series of detailed images of the inside of the brain, taken from different angles.

        2. Nuclear magnetic resonance (NMR)

        To develop this technique, the use of a large electromagnet, radio waves, and a computer are used to capture detailed images of the brain. With NMR, better quality images are obtained than those obtained with CT. This technique was a breakthrough in brain imaging research.

        3. Positron Emission Tomography (PET)

        It is considered to be one of the most invasive techniques. It is used to measure the metabolic activity of different regions of the brain.

        This is obtained by injecting the patient with a radioactive substance that binds to glucose and then binds to cell membranes of the central nervous system through the bloodstream.

        Glucose accumulates at a high rate in areas of higher metabolic activity. This makes it possible to identify a decrease in the number of neurons in a certain area of ​​the brain, in the event that hypometabolism is detected.

          4. Functional magnetic resonance (fMRI)

          This technique is another variation which is used to visualize the regions of the brain which are active at certain times or during certain activities; which is achieved by detecting the increase in oxygen in the blood in these more active areas. It provides images with better resolution than other functional imaging techniques.

          5. Electroencephalogram (EEG)

          A technique started in the 1920s that is used to measure the electrical activity of the brain by placing electrodes on the skull.

          The purpose of this tool is study brain wave patterns associated with specific behavioral states (eg beta waves are associated with a state of alertness and also wakefulness; while delta waves are associated with sleep) and also allows detection of possible neurological disorders (eg epilepsy). ).

          A major advantage of MEG by compared to EEG is to be able to reveal the three-dimensional location of the group of neurons that generates the measured magnetic field.

            Advantages and disadvantages of magnetoencephalography

            As with any resource for making the brain an understandable reality and capable of providing relevant data, magnetoencephalography has certain advantages and disadvantages. Let’s see what they are.

            Advantages

            According to Zhang, Zhang, Reynoso and Silva-Pereya (2014), the advantages of this revolutionary brain measurement technique are as follows.

            As stated before, this is a non-invasive test, so it is not necessary to penetrate inside the skull with some kind of instrument specialized in the measurement of magnetic fields emitted by neural currents in different regions of the brain. In addition, it is the only completely non-invasive neuroimaging technique. Of course, its use does not hurt.

            In addition, it allows the possibility of seeing functional images of the brain at times when it is inferred that there may be a disorder but there is no anatomical evidence to prove it. That is why this test shows the local point of brain activity with great precision.

            Another advantage that has been found is that it also offers the possibility of examine infants who have not yet acquired the ability to emit behavioral responses.

            Finally, according to Maestu et al. (2005) the MEG signal is not degraded by crossing the different tissues; something that happens with the currents captured by the EEG. This allows magnetoencephalography to measure neural signals directly and in milliseconds.

            Disadvantages

            According to Maestu et al. (2005) MEG presents some limitations which prevent it from being the definitive technique in the field of the study of cognitions. These limits are:

            • Impossibility of picking up sources found in the depths of the brain.
            • High sensitivity to the environment where the test takes place.

            Bibliographical references

            • From April, A. et al. (2009). Psychobiology. In De l’Abril, A. et al. Foundations of psychobiology (pp. 1-25). Madrid: Sanz and Torres.
            • Maestu, F. et al. (2005). Magnetoencephalography: a new tool for the study of basic cognitive processes. Psychotheme, 17 (3): p. 459-464.
            • Zhang, I.; Zhang, W.; Reynoso, V .; Silva-Pereyra, J. (2014). Magnetoencephalography: mapping of the spatio-temporal dynamics of neuronal activity. Psychological sum, 21 (1): p. 45 – 53.

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