Evoked potential: what it is and how it helps to study the brain.
A concept linked to neuropsychological evaluations of brain functioning.
In psychological assessment there are different types of tests: objective, subjective, constructive, projective... Depending on what they aim to assess, how they do it, and their underlying theoretical orientation. In this article we will talk about an objective test, the evoked potential test.
This is a neurophysiological test that came into use in 1947. It allows the evaluation of neuronal activity through stimulation of the brain. It is also used to determine the presence of alterations, diseases such as multiple sclerosis and tumors. We will know its characteristics, uses, operation and types.
The evoked potential test: an objective test.
In psychological assessment, the evoked potential test is classified as an objective psychophysiological an objective psychophysiological technique.
Objective tests imply that the administration, recording, scoring and analysis of their data are performed from apparatus. By contrast, they are tests with very low ecological validity, since they are used in artificially created situations.
This particular test is minimally invasive, painless (although it may cause some discomfort in some people) and safe, which was first used 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, auditory and visual). of different types (auditory, visual, somatosensory,...), i.e. stimuli coming from any modality, and of short duration. This type of response seems to be related to the intellectual level of the person.
How does it work?
The evoked potential test is used to detect possible diseases related to the functioning of brain activity (neural connections). (neuronal connections).
Specifically, what it does is to determine the speed of the functioning of the 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 serves to ensure that neuronal transmissions occur quickly and efficiently.
In other words, the test helps to determine whether myelin damage is present.. We are therefore talking about a process of demyelination, which is typical in diseases such as multiple sclerosis. Thus, the evoked potential test would make it possible to detect this type of disease (or confirm its diagnosis).
Uses and functions.
In addition to detecting possible diseases such as multiple sclerosis, the evoked potential test makes it possible to detect alterations in brain function that have to do with the conductance of neurons, i.e., with the fluid of the brain.that is to say, with the flow of electricity in the brain and with how information is transmitted (with greater or lesser fluidity, speed, etc.).
This technique will be useful when previous neuropsychological examinations are not sufficiently clear, or do not allow to diagnose the pathology with accuracy or reliability. It can be applied in cases of suspicion of any alteration.
On the other hand, the evoked potential technique also allows detecting 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, it can also is used on comatose patients in order to assess their brain function or activity.in order to evaluate their brain function or activity.
How is it used?
In relation to the above mentioned, the evoked potential test basically detects if the neuronal conduction system (electrical) 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 patient's pathology.
This test is especially useful when a certain disease or lesion does not produce evident symptoms, or produces "silenced" symptoms, as it corroborates a previous suspicion of disease evaluated with other evaluated with other types of neuropsychological tests of a more clinical nature.
On the other hand, in the case of a disease affecting brain electrical activity, the evoked potential test can provide information on the evolution of the disease itself; in the case of a lesion in the central nervous system, it helps to determine which area(s) is (are) affected and to what extent (extent of the affected area).
Finally, this test helps to define changes that have occurred in the functioning and/or neuropsychological state of a person (e.g. in a patient with dementia). (for example in a patient with dementia, since dementia is progressive).
How is it applied?
The potential test is easy to apply; for this purpose, generally the electrodes are placed on the person's scalp (ideally, the person's scalp is (ideally, the hair should be washed the day before and no additional products should be used). Specifically, the electrodes are placed on the areas to be stimulated.
Once the electrodes have been placed in the corresponding areas (which will vary in each case), the investigator 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.The results of the evoked potential test will be collected by means of sensory stimuli, which can be of three types: auditory, visual and somatosensory.
Subsequently, the results "emitted" by the brain will be collected, which allow to determine the activity of the brain, as well as possible lesions in the myelin layer covering the neurons.
Types
There are three types of evoked potentials 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, etc., may be used.etc.
It is useful to diagnose hearing difficulties, different types of deafness, etc. In this case, the electrodes will be placed on the scalp and on the 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 involving optic nerve involvement.. The stimulus or stimuli will consist of a screen with black and white pictures, which the tested subject will have to observe.
3. Somatosensory stimulation
Finally, the third type of evoked potential test is the one performed on the basis of somatosensory stimulation (the test is called PESS for short). It is used to diagnose problems that occur in the spinal cord and can cause different types of symptoms. and can cause different types of symptoms, such as numbness or paralysis in the legs or arms.
The stimuli applied are electrical (of 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 conditions of the person that may interfere with the results of the evoked potential test. For this reason, the professional who performs the test should take them into account.
Some of the most common factors or variables that can interfere areThe most common factors or variables that can interfere with the results of the evoked potential test are: if the person being tested has an inflamed middle ear (in the case of the auditory test) or has some type of hearing impairment (this condition can affect all sensory modalities), has severe myopia (in the visual test), has movement alterations such as Muscle spasms in the neck or head, etc.
Bibliographic references:
- Fernández-Ballesteros, R. (2005). Introduction to Psychological Assessment I and II. Ed. Pirámide. Madrid.
- Moreno, C. (2005). Psychological assessment. Concept, process and application in the areas of development and intelligence. Ed. Sanz y Torres. Madrid.
- Walsh, P., Kane, N. & Butler, S. (2005). The clinical role of evoked potentials. British Medical Journal, 76(suppl. 2): 16-22.
(Updated at Apr 12 / 2024)