Evoked Potential: What It Is And How It Helps To Study The Brain
In psychological evaluation there are different types of tests: objective, subjective, constructive, projective… Depending on what they intend to evaluate, how they do it, and their underlying theoretical orientation. In this article we will talk about an objective test, the evoked potential test
It is a neurophysiological test that began to be used in 1947. It allows evaluating neuronal activity through stimulation of the brain. In addition, it is used to determine the presence of alterations, diseases such as multiple sclerosis and tumors. We will know its characteristics, uses, operation and types.
In psychological evaluation, the evoked potential test is classified as an objective psychophysiological technique
Objective tests imply that the administration, recording, scoring and analysis of your data is carried out using devices. On the other hand, they are tests with very low ecological validity, since they are used in artificially created situations.
This specific test It is minimally invasive, painless (although it may cause some discomfort in some people) and safe, which was used for the first time in 1947.
The test evaluates a very specific type of psychophysiological response. Specifically, It is used to study the electrical activity of the brain in response to sensory stimuli of different types (auditory, visual, somatosensory,…), that is, stimuli that come from any modality, and of short duration. This type of response seems to be related to the person’s intellectual level.
How does it work?
The evoked potential test It is used to detect possible diseases related to the functioning of brain activity (neural connections).
Specifically, what it does is determine the speed of functioning of brain connections; That is, if it is too slow, it is likely that the myelin sheaths, a layer that covers the neurons of the nervous system, are damaged. Myelin helps neuronal transmissions occur quickly and efficiently.
That is, the test helps determine if there is damage to the myelin We are then talking about a demyelination process, typical in diseases such as multiple sclerosis. Thus, the evoked potential test would allow us to detect this type of disease (or confirm its diagnosis).
Uses and functions
In addition to detecting possible diseases such as multiple sclerosis, the examination of the evoked potential allows us to find alterations in brain functioning that have to do with the conductance of neurons that is, with the flow of electricity at the brain level and with how the information is transmitted (with greater or lesser fluidity, speed, etc.).
This technique will be useful when previous neuropsychological tests are not clear enough, or do not allow the pathology to be diagnosed with accuracy or reliability. It can be applied in cases of suspected alteration.
On the other hand, the evoked potential technique also allows us to detect alterations in vision (such as some types of blindness) when the optic nerve is damaged. In addition, it can help in the diagnosis of tumors.
Finally, also It is used in patients in a coma in order to evaluate your brain function or activity.
How is it used?
In relation to the aforementioned, what the evoked potential test basically does is detect if the neuronal (electrical) conduction system is damaged. This system has to do with the different senses (hearing, sight, hearing,…), and it may happen that one of them is damaged, and the others are not, always depending on the pathology that the patient presents.
This test is especially useful when a certain illness or injury does not produce obvious symptoms, or produces “silenced” symptoms, since allows corroboration of a previous suspicion of disease evaluated with other types of more clinical neuropsychological tests.
On the other hand, in the event that there is a disease that affects brain electrical activity, the evoked potential test provides information about the evolution of the disease itself; In the event of an injury to the Central Nervous System, it helps determine which area(s) is(are) affected and to what extent (extent of the affected area).
Finally, this test helps define changes that have occurred in the functioning and/or neuropsychological state of a person (for example in a patient with dementia, since it is progressive).
How does it apply?
The potential test is easy to apply; For this, generally The electrodes are placed on the person’s scalp (Ideally, she should wash her hair the day before, and not use additional products). Specifically, the electrodes will be placed on the areas that are going to be stimulated.
Once the electrodes are placed in the corresponding areas (which will vary in each case), The researcher or professional who applies the evoked potential test will proceed to stimulate the examined subject through sensory stimuli, which can be of three types: auditory, visual and somatosensory.
Subsequently, it will collect the results that the brain “emits”, and which allow determining its activity, as well as possible injuries to the myelin layer that covers the neurons.
Guys
There are three types of evoked potential tests, depending on the type of stimulus applied:
1. Auditory stimulation
When the stimuli applied are auditory, we speak of an auditory evoked potential (AEP) test. Thus, the stimuli will be auditory and Different types of tone, intensity, noises can be used etc.
It is useful for diagnosing hearing difficulties, different types of deafness, etc. In this case, the electrodes will be placed on the scalp and earlobes.
2. Visual stimulation
Here the stimuli are visual, and the test is a visual evoked potential (VEP) test. This type of test will allow us to diagnose vision problems that involve damage to the optic nerve The stimulus or stimuli will consist of a screen with black and white squares, which the examined subject must observe.
3. Somatosensory stimulation
Finally, the third type of evoked potential test is the one performed using somatosensory stimulation (the test in short is called PESS). Used to diagnose problems that appear in the spinal cord and they can cause different types of symptoms, such as numbness or paralysis in the legs or arms.
The stimuli applied are electrical (mild intensity), and in this case, the electrodes are placed in different areas that may vary, such as the knees or wrists.
Precautions and considerations
There are some person conditions that can interfere with the results of the evoked potential test. That is why the professional who applies it must take them into account.
Some of the most common factors or variables that can interfere are: that the person being examined has an inflamed middle ear (in the case of the hearing test) or that he or she has some type of hearing disability (this condition can affect all sensory modalities), that he or she has severe myopia (in the visual test), that presents alterations in movement such as muscle spasms in the neck or head, etc.
