Magnetoencephalography: What It Is And What It Is Used For
Magnetoencephalography is one of the best-known neuroimaging techniques used both in clinical intervention programs and in lines of research on the human brain. Therefore, it constitutes an example of how technology helps us know ourselves better.
In this article We will see what magnetoencephalography consists of and how it works and what are its uses.
There is no doubt that The brain is a system made up of millions of extremely complex biological processes, among which it is worth highlighting language, perception, cognition and motor control. That is why for thousands of years this organ has aroused great interest from all types of scholars who have provided various hypotheses about its functions.
A few years ago, in order to measure cognitive processes, behavioral measurement techniques were used; such as reaction time measures and pencil-and-paper tests. Later, throughout the 90s, great technological advances made it possible to record brain activity that was related to these cognitive processes. This represented a great qualitative leap in this area of research and a complement to the traditional techniques that are still used.
Thanks to these advances, today it is known that in Brain function involves billions of neurons that are interconnected forming what are known as synaptic connections and these connections are set in motion by electrical impulses in the brain.
Each neuron can be said to work as if it were a “small electrochemical pump” that contains ions, which are charged with electricity, and are in continuous movement, both inside and outside the cell membrane of the neuron. When neurons are charged, they provide a flow of current to the cells, and these in turn are stimulated ; causing what is known as an action potential that causes the neuron to trigger the flow of charged ions.
This electrical potential moves until it reaches the presynaptic region and then releases neurotransmitters into the synaptic space that access the cellular postsynaptic membrane and immediately cause changes in intra- and extracellular ionic flow.
When several synaptically interconnected neurons and cells activate simultaneously, they provide a flow of electric current accompanied by a magnetic field and, accordingly, they flow to the cerebral cortex.
It is estimated that in order to generate a magnetic field, measurable through measuring instruments that are placed on the head, It is necessary that 50,000 neurons or more are active and interconnected If it were the case that there were electric currents moving in opposite directions, the magnetic fields that accompanied each current would cancel each other out (Hari and Salmelin, 2012; Zhang et al., 2014).
These complex processes can be visualized thanks to neuroimaging techniques, among which is one that we want to highlight and will address in more detail in this article, magnetoencephalography.
What is magnetoencephalography?
Magnetoencephalography (MEG) is a neuroimaging technique that is used to measure the magnetic fields that are produced through the electrical currents of the brain These electrical currents are produced through the neuronal connections that exist throughout the brain in order 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 sleeping.
The MAG is also a non-invasive medical test; Therefore, during its handling it is not necessary to introduce any instrument into the skull to detect interneuronal electrical signals. This tool allows us to study the human brain ‘in vivo’, so We can detect various brain mechanisms in full operation while the person receives certain stimuli or performs some activity At the same time, it allows us to locate any anomaly if there is one (Del Abril, 2009).
With MEG we can visualize mobile three-dimensional images with which we can accurately detect, in addition to anomalies, their structure and the function they perform. This allows professionals to investigate whether there is any relationship with the personality of the subjects who present these anomalies, study whether genetics plays a relevant role and even contrast whether they influence cognition and emotions.
Who is in charge and where is MEG usually used?
The specialized professional who is in charge of performing these brain evaluation tests is the radiologist doctor
This test, as well as the rest of the neuroimaging techniques, is usually carried out in hospital contexts where all the necessary machinery is available.
The systems that perform MEG are carried out in a specialized room that must be protected in order to prevent interference that could occur through the strong magnetic signals that the environment would produce if it were carried out in any place.
To carry out this test The patient is seated and a “helmet” containing magnetic sensors is placed on his head Using a computer, the signals that provide the MEG measurement are detected.
Other techniques that allow studying the brain ‘in vivo’
Neuroimaging techniques, also known as neuroradiology tests, are those that allow obtaining an image of the brain structure in full operation. These techniques allow the study of disorders or anomalies of the central nervous system in order to find a treatment
According to Del Abril et al. (2009), the techniques most used in recent years, apart from magnetoencephalography, are the following.
1. Computed axial tomography (CAT)
This technique is used through a computer that is connected to an X-ray machine The goal is to capture a series of detailed images of the inside of the brain, taken from various angles.
2. Nuclear magnetic resonance (MRI)
To develop this technique, the use of a large electromagnet, radio waves and a computer is used in order to capture detailed images of the brain. With MRI, images are obtained with higher quality than those obtained with CT This technique represented a great advance for research using brain images.
3. Positron emission tomography (PET)
It is considered one of the most invasive techniques. It is used to measure the metabolic activity of different regions of the brain.
This It is achieved by injecting the patient with a radioactive substance that binds to glucose and subsequently joins the cell membranes of the central nervous system through the bloodstream.
Glucose accumulates at high speed in areas with greater metabolic activity. This makes it possible to identify a decrease in the number of neurons in a certain area of the brain, if hypometabolism is detected.
4. Functional magnetic resonance imaging (fMRI)
This technique is another variant that is used to visualize the regions of the brain that are active at certain times or when carrying out some activity; which is achieved by detecting the increase in blood oxygen in those most active areas. Allows you to obtain images with better resolution than other functional imaging techniques
5. Electroencephalogram (EEG)
Technique initiated in the 1920s that is used to measure the electrical activity of the brain by placing electrodes on the skull.
The objective of this tool is to investigate the patterns of brain waves associated with specific behavioral states (e.g., beta waves are associated with a state of alertness and also wakefulness; while delta waves are associated with sleep) and also allows the detection of possible neurological alterations (e.g., epilepsy).
A great advantage that MEG has over EEG is being able to reveal the three-dimensional location of the group of neurons that is generating the magnetic field that is being measured.
Advantages and disadvantages of Magnetoencephalography
As with any resource to make 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), among the advantages of this revolutionary brain measurement technique, the following stand out.
As said previously, it is a non-invasive test, so it is not necessary to penetrate the inside of the skull with any type of instruments specialized to be able to measure the magnetic fields emitted by neuronal currents in the various regions of the brain. What’s more, it is the only completely non-invasive neuroimaging technique. Of course, using it doesn’t hurt.
Furthermore, it allows the possibility of see functional images of the brain at times when it is assumed that a disorder may be present but there is no anatomical evidence that can prove it. That is why this test shows the local point of brain activity with high 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 make behavioral responses
Finally, according to Maestu et al. (2005) the MEG signal is not degraded by its passage through different tissues ; something that does happen with the currents captured by the EEG. This allows magnetoencephalography to measure neuronal signals directly and in a matter of milliseconds.
Disadvantages
According to Maestu et al. (2005) the MEG presents some limitations that prevent it from being the definitive technique in the field of the study of cognitions These limitations are:
Impossibility of capturing sources found in the depths of the brain.
High sensitivity to the environment in which the test is carried out.
