Electroencephalogram: process, results and common doubts

Epilepsy and other neurological disorders are detected early thanks to the electroencephalogram. We tell you what the test consists of.

Last update: September 17, 2022

The brain is made up of a vast and complex network of specialized cells called neurons. It communicates through electrical stimuli that can be analyzed using the electroencephalogram.

The health of the human brain and the entire central nervous system (CNS) can be assessed through a large number of tests. In this way, it is possible to detect structural abnormalities and nervous function disorders in time. Electroencephalography, tomography and magnetic resonance imaging are some of the most common tests.

The electroencephalogram is the method of choice for the diagnosis of seizures and epilepsy, according to specialists. This medical tool has saved millions of lives. Its usefulness goes beyond diagnosis.

What is the electroencephalogram?

It is a functional exploration technique that measures the electrical activity of the brain in real time. According to studies, Hans Berger in 1929 was the one who coined the term electroencephalogram (EEG) to describe the recording of brain electrical fluctuations captured by electrodes attached to the scalp.

Neurons are always active, transmitting electrical impulses throughout the CNS. The EEG captures and amplifies these electrical signals, representing them in lines with undulations that define the activity of the different regions of the brain.

In most cases, the electroencephalogram is performed in the basal state and subject to activation methods, such as hyperventilation or visual stimulation. In fact, some professionals recommend obtaining a detailed brain recording during sleep. In addition, there are 24-hour follow-up EEG.

This test results in normal and abnormal patterns that help diagnose characteristic injuries or disorders, such as seizures. For this reason, it is a complementary study widely used in neurological consultation.

Neurons have electrical activity that we can measure. The tracing of that measurement is interpreted in neurology.

Why is this test done?

It is of medical interest to evaluate the state of brain electrical activity in those with suspected episodic or persistent nerve disturbances. Among the most frequent indications of the electroencephalogram are the following:

  • Alteration of higher functions, such as memory and consciousness.
  • Epilepsy or other seizure syndromes.
  • Sleep disorders, such as insomnia.
  • Encephalitis and other CNS infections.
  • Cerebrovascular disease (CVD).
  • Monitoring during brain surgery.
  • Cranioencephalic trauma.
  • Cranial tumors.
  • Alzheimer’s.

Similarly, EEG is useful to confirm brain death in patients who are in a deep coma. Likewise, it offers data of interest in drug-induced anesthesia.



Possible risks and contraindications

Usually the electroencephalogram It is a fairly safe technique and does not cause any type of pain or adverse reaction.. Controlled methods are sometimes used to induce seizures, such as light stimulation or hyperventilation. However, the specialist is trained to provide medical care if necessary.

Preparations for an EEG

There are several recommendations that should be followed before performing an electroencephalogram. In this way, we ensure that the test is carried out correctly and without errors in the results.

In this regard, preparations for the EEG include the following:

  • wash hair the night before or several hours prior to the study.
  • Avoid using conditioners, gels, oils, creams or hair sprays, as they can make it difficult for the electrodes to adhere.
  • In the case of hair extensions, ask the health provider for instructions.
  • Do not change or suspend any usual medication without indication. Consult the doctor for more information.
  • Avoid consuming foods or drinks with caffeine 6 to 8 hours before the test.
  • Sleeping less than usual in the event of an EEG during sleep.
  • Do not take energy drinks or other products to stay awakeespecially if you have to sleep during the test.

How is the electroencephalogram performed?

This test is performed by a professional EEG technician in a medical center, private practice, or laboratory. He will be in charge of guiding the patient throughout the process in a safe and simple way..

During the test

The person to be evaluated must lie down on a stretcher or reclining chair. Then, a technician will measure the different diameters of the skull and mark the points where the electrodes will be placed. These discs do not produce any type of pain and are responsible for recording brain activity.

In general, the electrodes are placed on the scalp using a special adhesive. Sometimes, caps that include the electrodes are used. The latter will be connected by cables to an instrument that will capture and amplify the electrical signal.

During the test, the person evaluated must remain relaxed and with their eyes closed. Occasionally, the technician may ask you to open and close your eyelids, take a deep, rapid breath, perform a calculation, or look at a bright light. In addition, the patient may also be asked to sleep during the evaluation.

In most cases, body movements are captured on video during the EEG. In this way, the doctor can combine the recording of brain waves with these images to obtain a more accurate diagnosis.

On the other hand, an ambulatory EEG may be indicated for those who require longer monitoring. This unit will accompany the patient throughout the day and will record the brain’s electrical record while normal activities are carried out.



after test

The basic EEG usually takes 20 to 40 minutes, once the electrodes are in position. However, as we mentioned before, some tests may require the patient to sleep, which lengthens the exam.

At the end of the EEG, the technician will remove the electrodes from the scalp. Some people may require sedatives to induce sleep, so a friend or family member will need to accompany you home after the evaluation. If you do not ingest any type of sedative, you can resume normal daily activities.

The electrodes pick up brain electricity. It is ideal that the hair is not treated with products 24 hours before.

Electroencephalogram results

This test provides a printed record of brain activity, represented by waves that are drawn with different frequencies and amplitudes. The characteristics of the EEG vary according to the state of consciousness. In this sense, the waves are usually faster when the patient is awake and slower during sleep phases.

Health professionals are the only ones trained to interpret an electroencephalogram and offer an accurate diagnosis. In general, the presence of broad, sharp waves could indicate a seizure syndrome, such as epilepsy. Bleeding, tumors, and brain infarcts are other common causes of abnormal findings.

If you have any concerns, do not hesitate to consult a specialist in neurology.

EEG: a useful tool to assess brain status

The electroencephalogram is a safe and useful for assessing the health of the brain and the entire central nervous system. Early diagnosis of neurological diseases improves the quality of life of many people and prevents long-term complications. Its practice and interpretation is exclusive to health professionals.

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