Evoked potential: what it is and how it helps study the brain

In psychological assessment, there are different types of tests: objective, subjective, constructive, projective … depending on what they intend to assess, how they do it and their underlying theoretical orientation. In this article we will talk about an objective test, proof of the evoked potential.

It is a neurophysiological test which began to be used in 1947. It makes it possible to evaluate neuronal activity by brain stimulation. In addition, it is used to determine the presence of disorders, 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 test of evoked potential is classified as an objective psychophysiological technique.

    Objective testing means that the administration, recording, scoring and analysis of your data is done from devices. On the contrary, they are tests with very low ecological validity, as they are used in artificially created situations.

    This particular test it is minimally invasive, painless (Although it can cause some discomfort in some people) and harmless, it was first used in 1947.

    The test assesses a very specific type of psychophysiological response. More precisely, is used to study the electrical activity of the brain in response to sensory stimuli of different types (auditory, visual, somatosensory, …), that is to say 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 it works?

    Proof of the evoked potential is used to detect possible diseases related to the functioning of brain activity (Neural connections).

    Specifically, it determines the speed at which brain connections work; that is, if it is too slow, it is likely that the myelin sheaths, a layer that covers neurons in the nervous system, are damaged. Myelin is used to induce fast and efficient neuronal transmissions.

    In other words, the test helps determine if there is a myelin injury. This is called a demyelination process, typical of diseases such as multiple sclerosis. Thus, the test of the evoked potential would make it possible to detect this type of disease (or to confirm its diagnosis).

      Uses and functions

      In addition to detecting possible diseases such as multiple sclerosis, the examination of the evoked potential makes it possible to find changes in brain function linked to the conductance of neuronsThat is to say with the electric fluid at the level of the brain and with the way in which the information is transmitted (with more or less fluidity, speed, etc.).

      This technique will be useful when previous neuropsychological examinations are not sufficiently clear or do not allow the pathology to be diagnosed with precision or reliability. It can be applied in case of suspicion of any alteration.

      On the other hand, the evoked potential technique also makes it possible to detect alterations in vision (such as certain types of blindness), when the optic nerve is damaged. Plus, it can help diagnose tumors.

      Finally also used in patients in a coma, In order to assess their brain function or activity.

      How is it used?

      Related to the above, the evoked potential test what it essentially does is to detect if the neural (electrical) conduction system is damaged. This system concerns the different senses (hearing, sight, hearing, …), and it can happen that one of them is damaged, and the others are not, always according to the pathology presented by the patient.

      This test is particularly useful when a particular illness or injury does not produce obvious symptoms or produces “silenced” symptoms, such as allows to corroborate a previous suspicion of disease evaluated with another type of neuropsychological test more clinical type.

      On the other hand, in the event of a disease affecting the electrical activity of the brain, the test of the evoked potential makes it possible to disseminate information on the evolution of the disease itself; in the event of damage to the central nervous system, it makes it possible to determine which area (s) is (are) affected and to what extent (extent of the affected area).

      Finally, this test helps define changes in a person’s functioning and / or neuropsychological state (For example in a patient with dementia, as this is progressive).

      How is it applied?

      The potential test is easy to apply; therefore, generally the electrodes are placed on the scalp of the person (Ideally, she should wash her hair the night before and not use any extra products). More precisely, the electrodes will be placed on the areas to be stimulated.

      Once the electrodes are placed in the corresponding areas (which will vary in each case), the researcher or the professional applying the test of the evoked potential will proceed to the stimulation of the examined subject, Through sensory stimuli, which can be of three types: auditory, visual and somatosensory.

      Later, it will collect the results that the brain “emits”, and which make it possible to determine the activity of this one, as well as possible injuries to the layer of myelin which covers the neurons.


      There are three types of evoked potential tests, depending on the type of stimulus applied:

      1. Hearing stimulation

      When the applied stimuli are auditory, it is called 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 problems, different types of deafness, etc. In this case, the electrodes will be placed on the scalp and the earlobe.

      2. Visual stimulation

      Here the stimuli are visual and the test is a visual evoked potential (VEP) test. This type of test it will allow us to diagnose vision problems involving damage to the optic nerve. The stimulus or stimulus will consist of a screen with black and white squares, which the examined subject should observe.

      3. Somatosensory stimulation

      Finally, the third type of potential test mentioned is that carried out from somatosensory stimulation (the test is abbreviated as PESS). is used to diagnose problems that appear in the spinal cord and which can cause different types of symptoms, such as numbness or paralysis of the legs or arms.

      The applied stimuli are electrical (light intensity), and in this case the electrodes are located in different areas which may vary, such as the knees or the wrists.

      Precautions and Considerations

      Certain conditions in the person may interfere with test results for the evoked potential. This is why the professional who applies it must take it into account.

      Some of the most common factors or variables that can interfere are: Whether the examined person has an inflamed middle ear (in the case of the hearing test) or has some type of hearing impairment (this condition can affect all sensory modalities), has severe myopia (in the test visual), which presents with movement alterations such as muscle spasms in the neck or head, etc.

      Bibliographical references:

      • Fernández-Ballesteros, R. (2005). Introduction to psychological assessment I and II. Ed. Pyramid. Madrid.
      • Moreno, C. (2005). Psychological assessment. Concept, process and application in the fields of development and intelligence. Ed. Sanz and Torres. Madrid.
      • Walsh, P., Kane, N. and Butler, S. (2005). The clinical role of evoked potentials. British Medical Journal, 76 (suppl. 2): 16-22.

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