Electroencephalogram (EEG)

"The first EEGs and until a few years ago were performed on paper; however, today the digital EEG is much more used, since it allows better data storage and analysis".


The electroencephalogram (EEG) is a study of the brain function that collects the electrical activity of the brain in a basal situation and with activation methods, such as hyperventilation and photo-stimulation. It is also convenient to record during sleep.

The electrical signal collected is amplified and represented in the form of lines, interpreting the activity of the different brain areas over time.

There are normal patterns and abnormal patterns that make one suspect of characteristic injuries or illnesses.

It is, therefore, a means of functional diagnosis of brain diseases complementary to other studies, especially radiological ones (TAC, magnetic resonance).

In addition to the usual records, 24-hour electroencephalograms or electroencephalographic and video studies are performed for 1-6 days.

In these cases, the technique is similar, but more collaboration is required from the patient, since he or she must remain under control during the entire time of the study.

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When is an electroencephalogram performed?

The EEG serves to observe the electrical functioning of the brain. It is of interest to know its normality or not in patients with alteration of the cerebral functions, either in a persistent way or in an episodic way.

It can detect alterations of the whole brain or of some areas. It is useful to observe alterations in lesions (tumors, hemorrhages, encephalitis, traumatisms, among others) and diffuse lesions (toxic, metabolic, infectious, etc.)

It is essential to perform the EEG in patients whose symptoms or complaints are deteriorating level of consciousness (drowsiness, stupor, coma), loss of intellectual faculties (memory loss, dementia) or episodes that suggest epileptic seizures (epilepsy is a disease in which the brain discharges electrical impulses suddenly producing seizures).

Most frequent indications of this test:

  • Headaches.
  • Epilepsy.
  • Movement disorders.
  • Sleep disorders.

Do you have any of these diseases?

You may need to have an electroencephalogram

How is the electroencephalogram performed?

The EEG is a simple procedure. It does not require any special preparation or fasting.

Once the electrodes have been placed on the patient (with a rubber or plastic cap or with electrodes attached individually), he or she sits in an armchair and the recording of brain activity begins. This must be recorded at rest, with eyes closed and open, and in activation maneuvers, such as hyperventilation (deep breathing) for 3 minutes, and stimulation with a flash type light at different frequencies.

Once the test is finished, the electrodes are removed and the patient can continue his normal activities

There may be some paste left in the hair or the mark on the skin from the pressure of the electrodes. Both problems are minimal and are solved in a few minutes, when combing, and completely when washing the head.

Sometimes you have to go to the EEG after having slept little during the previous night, you can request the doctor when looking for some abnormalities that are caused by lack of sleep.

The EEG usually lasts about 15-25 minutes.

Only can not be made in patients with allergies to materials that are placed attached to the scalp (conductive paste, metal electrodes, plastic or rubber helmet), which is very rare.

  • It is advisable not to wear a very special hairstyle or use hairspray or other hair products, because you may have to rub the electrodes more if there is more resistance from dyes or products used on the scalp.
  • You must communicate if you have allergies to any components.
  • Also, it is possible that in some patients photo-stimulation or hyperventilation may trigger peculiar episodes, so it is advisable to report if such propensity is already known.

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.