Electroencephalogram (EEG): what is it and how is it used?

The word electroencephalogram is not something unknown today. Many people, whether for medical or research purposes, have already had it. And if this is how cinema, literature or popular wisdom can make us think of the typical image of a person with some kind of helmet full of connected electrodes.

But know what it is, what it measures exactly, what it is used for or how it works an electroencephalogram may not be so well known. That is why, in this article, we will look at different aspects of this measuring instrument so widely used in the field of medicine.

What is an electroencephalogram?

The electroencephalogram is a physiological assessment technique used to study how the nervous system is functioning by recording the electrical activity of the brain, especially the cerebral cortex.

To understand the meaning of this technique, it should be borne in mind that brain activity is based on the emission and transmission of electrochemical impulses, signals of nervous activity that can be detected using the techniques. appropriate. Thus, thanks to an electroencephalogram, it is possible detect the pattern of normal functioning of our brain and activation of the brain or parts of it in the face of external or internal stimulation.

In this technique an instrument called an electroencephalogram is used, Which records the electrical activity of what is connected. This instrument receives information from a series of electrodes which would be located in certain areas of the patient’s head and with which neuronal activity is recorded.

What is he measuring?

The electroencephalogram makes it possible to measure, as we have mentioned, electrical activity of the brain. Whatever the purpose of the encephalogram, this activity can take the form of several types of waves.

Measurements can be taken while awake or asleep, depending on the purpose for which the test is being performed. Thanks to the electrodes, the measuring system detects the emission of brain waves and their speed, form, duration and frequency of emission.

Types of waves

The captured waves they can be alpha, beta, theta and delta. Each will train the EEG to draw one or another wave frequency pattern.

Alpha waves they appear in moments of relaxation or when faced with tasks that do not require concentration or effort.

Beta waves generally reflect the achievement of intense mental effortUsually appearing when we are awake or during REM sleep.

Theta waves are observed in the same way as alpha waves when we are relaxed, but in this case they are more frequent at times when in addition to being relaxed we sleep, Being the most predominant wave type during phase two of non-REM sleep.

Finally, the delta waves they are the ones that are linked to deep sleep, Being those that have traditionally been linked to rest and repair of nerve tissue.

The encephalogram can measure both the general pattern of brain function and the differences between some areas with others, by analyzing the differences in voltage between different areas.

    How the test works

    The basic operation of this technique is not very complex. The test is based on the placement of a series of electrodes at strategic points on the headFixation on a small core of tissue previously placed on the scalp of the patient or subject of study or directly on the scalp.

    The register used measures a voltage difference between two electrodes, Be these placed in pairs to be able to carry out measurements.

    Phases of use of the encephalograph

    First, the test is prepared, sitting the subject to be evaluated and fixing the elements that make it possible to record brain activity. for that a type of hair gel is applied to improve the conduction of electricity and fix the electrodes more precisely, the snack is done then. They are generally placed around about twenty electrodes, creating an assembly which allows to obtain a good activity of the nervous system.

    In this assembly, it is common to use the 10/20 system, placing the electrodes in an equidistant manner in which they are separated by 10 to 20% of the axes of the brain. In addition, the set can be bipolar, if it is intended to record brain activity and the difference between two points, or monopolar if a specific point is compared to a point without brain activity.

    Once the electrodes are placedThe measurement is performed, by first recording the basal rhythm of the individual with both eyes closed and open, and then causing slight stimulation to observe the reaction of brain activity. Some common stimuli are mild light stimulation or hyperventilation of the patient. The subject may also be asked to do some type of physical or mental activity.

    As the test is performed, a series of results are obtained that indicate how the nervous system is acting and how it responds to stimulation.

    The results obtained by the measurement they can be saved either printed or directly reflected on a monitor. But the recording of the waves does not make sense in itself, having to carry out an analysis of the implications of the basal operation and / or of any alteration detected during the time which produced the recording.

    Uses and applications of the electroencephalogram

    In view of all of the above, it should be borne in mind that the use of the EEG is not done on a whim. It is only used for specific purposes and when certain diseases are suspected or an investigation is underway.

    In terms of research, the electroencephalogram is used in experiences in which it is necessary to know brain activity in a certain state or when performing specific actions. Thus, it is used to explore how our brain works and how it reacts to specific stimuli or activities. It also allows you to assess whether there are big differences between activating a particular area and others.

    It is used in medicine, can be used to detect if the brain is functioning normally, Monitor the state of consciousness during surgery or if there are alterations in the wave emission pattern.

    In this aspect, this type of technique tends to be used when the presence of disorders such as epilepsy is suspected (leading to voluntary seizures to record how and what is happening), dementias, encephalopathies, typical epidemics certain mental disorders and even differentiate between coma and brain death (While in the first there is brain activity, the second would show a flat electroencephalogram). It is also widely used to analyze sleep problems and disturbances.

    Contraindications and adverse effects

    The application of an electroencephalogram does not generally pose any problems in those in which it is carried out, being a non-invasive technique which has no contraindication in the majority of the population, not even in pregnant women.

    One of the rare exceptions is cases of epilepsy in which it could cause a seizure during the test, which in many cases is looked for to identify overactive areas. However, in severe cases, the risk of causing a new seizure should be assessed.

    Bibliographical references:

    • Gil-Nagel, A .; Parra, J .; Iriarte, JM and Kanner, A. (2002). Manual of electroencephalography. Madrid: McGraw-Hill, SAU
    • Niedermeyer, E. and da Silva, FL. (2005). Electroencephalography: basic principles, clinical applications and related fields. Lippincott Williams and Wilkins.
    • Ramos-Argüelles, F .; Alonso, MT; Egozcue, S .; Pabón, RM and Morales, G. (2009). Basic electroencephalography techniques: principles and clinical applications. Annals of the Six. Sant. Navarra, vol. 32 (Suppl. 3), Pamplona.

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