An electroencephalogram is a diagnostic test in which the electrical activity generated by the cerebral cortex is recorded. It does so by means of a series of electrodes that are enclosed in a special cap that is adapted to the skull.
This type of study is usually used to detect the following pathologies:
- Epilepsy
- Cognitive impairments
- Alterations of cerebral vascularization
- Alterations of the cerebral cortex, secondary to renal and/or hepatic failure.
- Brain death
- Status epilepticus (uncontrollable epileptic seizures).
The importance of electroencephalogram in epilepsy
This test is essential for monitoring and evaluating epileptic patients, since it detects alterations that may lead to new seizures if medical antiepileptic treatment is discontinued. For this reason, an electroencephalogram is usually requested before withdrawal of drugs, and if this proves to be normal, treatment can be discontinued with greater certainty.
In the case of cognitive impairment, significant alterations and slowing of brain rhythms may suggest a worse prognosis or a more rapid progression of dementia.
What does an electroencephalogram consist of?
During the procedure, a special cap containing electrodes is placed on the scalp. A gel is applied to each electrode to help record the electrical activity of the cerebral cortex. Normally, the test lasts between 20 and 25 minutes.
To perform this test, a quiet and dark environment is required. In addition, while the study is being performed, the patient is asked to open and close the eyelids, to breathe deeply for 1 minute and, finally, very intense lights at different frequencies are applied. In this way, the brain’s response to the stimuli is observed.
How is the preparation for this test?
It is necessary that the patient comes to the study with clean and dry hair. In addition, the patient is sometimes asked not to have slept beforehand, since some epileptic phenomena manifest themselves better with lack of sleep or during sleep.
Finally, it is not necessary to be fasting, i.e. it is possible to eat normally.
Analysis of the results
The results of an electroencephalogram are considered normal when there are no epileptic discharges in the cerebral cortex or when the brain rhythms are appropriate for the patient’s age, and are not slowed. In addition, it is important to note that when breathing deeply during hyperventilation, the response of the cerebral blood vessels is normal.
Neonates, infants and young children have different rhythms, as their brains are still forming. At about 8 to 10 years of age, brain rhythms already resemble those of an adult.
On the other hand, at older ages, from 80 to 90 years, and depending on the condition of the individual, it is normal and physiological for brain rhythms to slow down.
When should an electroencephalogram be performed?
It is a study that is usually requested by specialists in Neurology and Neurophysiology, Psychiatry or Pediatrics. In cases of childhood epilepsy, it is indicated to perform it every six months or a year, to determine if in the recording of brain activity there are discharges that can trigger new epileptic seizures.
In cases of cognitive impairment, EEGs are usually performed every six months or a year to analyze the evolution.
Finally, in patients who have not had seizures for several years, electroencephalograms may be spaced out and may not even be necessary.