Evoked potentials

"To evaluate the answers, you have to give several hundred stimuli and average the results".


Evoked potentials are diagnostic techniques that, by means of sensory stimuli (visual, auditory or tactile electrical) and the recording of the brain responses that these provoke, value the integrity of the stimulated sensory pathways. To evaluate these responses, several hundred stimuli must be given and the results averaged.

If the visual or auditory stimulus or the electrical sensation does not produce the expected wave in the right time and place, it means that there is some interruption of that nerve pathway and, therefore, this data will make us think of a precise type of disease.

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When are the evoked potentials indicated?

They serve to find lesions in the sensitive pathways that are stimulated and to classify them by suggesting some causes or others.

They are methods of evolutionary control of already known processes. They evaluate signs of progression or improvement of a disease that does not give clear symptoms or problems to the patient.

They are important tests in diseases such as optical neuritis, multiple sclerosis, deafness, head trauma, spinal cord or brain stem injuries, neuropathies, etc. An alteration of the potentials is going to help to its diagnosis or to its exclusion.

As they are waves independent of the patient's will, they are objective, conclusive data of injury or normality, which is very important for the correlation between the patient's complaints and the actual injury.

Sometimes, even the alterations of the pathways precede the presence of symptoms, helping the early diagnosis of diseases that can be treated and treated urgently.

Most frequent indications of this test:

  • Multiple sclerosis.
  • Hearing loss.
  • Optic Neuritis.
  • Cranial trauma.

Do you have any of these diseases?

It may be necessary to realize some evoked potentials

How are the evoked potentials realized?

No previous preparation is necessary to perform this test. The patient is placed some electrodes (they are stuck with conductive paste and collodion) on the scalp and earlobes and/or on the shoulder, neck, spine.

Later, it receives the different stimuli to obtain the corresponding evoked response. Thus, for the visual evoked potential, the patient receives a visual stimulus; for the auditory evoked potential, the auditory stimulus consists of hearing tones through an earphone; and the somatosensory evoked potentials are produced by electrical stimuli in the feet and hands.

To obtain a potential, several hundreds of stimuli must be averaged, so the tests are long. Usually they last, if the recording is done without setbacks, half an hour (for the auditory and visual ones) or one hour (for the PESS from the four extremities).

Cognitive potentials require the placement of all EEG electrodes, usually with a helmet. Then, the maneuver involving attention is performed, which is usually to distinguish between two types of sounds, counting or otherwise indicating the presence of one of them.

Several hundred stimuli must also be averaged, so it is a long test, usually over half an hour.

These techniques are safe and harmless to the patient, although there is a possibility of problems with the electrodes (allergic type).

The stimuli received can produce certain discomfort. The patient can end up tired, since they are long tests.

Sometimes, the electrical stimuli needed for the PESS can be annoying because of the sensation of cramp or pain.

Where do we do it?


The Neurophysiology Service
of the Clínica Universidad de Navarra

The Neurophysiology Service of the Clinic collaborates in the diagnosis and follow-up of patients with diseases affecting the central and peripheral nervous system.

We share research and teaching care objectives with Neurosurgery, Neurology and the Neurosciences Area of the Cima Universidad de Navarra.

The service to the neurological patient benefits from the findings of the research and the new generations of doctors learn to care for their patients with an optimistic sense for the real hope of finding effective cures.

Organized in diagnostic areas

  • Motor Control Area.
  • Electroencephalography Area.
  • Electromyography Area.
  • Sleep Area.
  • Area of Evoked Potentials.
  • Monitoring in the operating room.
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Why at the Clinica?

  • State-of-the-art diagnostic assistance with great work in research and teaching.
  • Specialized nursing team.
  • We work together with the Sleep Unit.