Electroencephalogram
An electroencephalogram is a procedure that uses electrodes to measure the brain's electrical activity, obtaining the wave pattern of the electrical impulses through which neurons in the cerebral cortex communicate.
General Description
The electroencephalogram, also known as an encephalogram or EEG, is a neurophysiological procedure that measures and records the electrical activity of neurons located in the cerebral cortex.
Brain neurons remain active at all times, both during wakefulness and sleep. They communicate through electrical impulses that appear as waves of varying intensity in the electroencephalographic recording. An abnormal wave pattern indicates some type of disorder.
To obtain the most accurate information possible, the encephalogram is performed with the brain both at baseline (at rest) and activated through hyperventilation or photostimulation, among other methods, as well as during sleep. Sometimes, it is necessary to record an encephalogram for an extended period, lasting 24 hours or several days, in which case a portable device is used that the patient carries continuously.
When is it indicated?
An electroencephalogram can detect any changes or abnormalities in normal brain activity that may indicate the presence of a pathology, such as:
- Epilepsy.
- Encephalopathies.
- Brain infection or inflammation.
- Sleep disorders, such as narcolepsy.
- Neurodegenerative diseases, such as dementia or Alzheimer's disease.
- Brain injuries due to trauma.
- Brain tumors.
- Brain hemorrhage.
- StrokeStrokeStroke .
- Creutzfeldt-Jakob disease.
Therefore, an electroencephalogram is usually indicated if the patient presents any of the following symptoms:
- Seizures or absence episodes.
- Fainting.
- Memory loss.
- Confusion, drowsiness.
- Recurrent headaches.
- Sleep disorders.
- Coma.
Additionally, EEG is commonly used to monitor brain activity during brain surgery or an induced coma and to confirm brain death (the so-called flat electroencephalogram).
How is it performed?
Several electrodes, which are flat metal discs, are placed across the patient's scalp. These must cover all regions of the cerebral cortex and the midline. To prevent them from shifting, they are attached to the skin with an adhesive paste. However, in some cases, a cap with built-in fixed electrodes is used.
The electrodes are connected to a device that amplifies brain signals and to a computer that records the electrical activity and displays it as wave patterns, either on paper or directly on a monitor in digital format. The activity must be recorded with the patient both with eyes open and closed, breathing deeply for a few minutes, and being stimulated by a flashing light at different frequencies (strobe light). In some cases, an EEG may also be performed while the patient is asleep, even throughout an entire night.
Risks
The electroencephalogram is a very simple and safe test with no associated risks.
However, if the patient has an epileptic disorder, they may experience a seizure during hyperventilation or photostimulation. If this occurs, they are immediately attended to by a specialist physician.
What to expect from an electroencephalogram
The test is performed with the patient lying on a stretcher or sitting in a chair. The specialist measures the patient’s head with a measuring tape and uses a special pencil to mark the points on the scalp where the electrodes will be placed. Then, the adhesive gel is applied, and the patches are attached. The patient may feel a strange or sticky sensation in their hair but will not experience any discomfort while the brain waves are recorded.
In addition to opening and closing their eyes, breathing deeply, and looking at the light, the patient may be asked to read a short text, perform calculations, or observe an image. If a sleep-deprived electroencephalogram is performed, the patient must fall asleep during the test (if they are unable to do so on their own, a sedative may be administered).
The total duration of a conventional encephalogram is about 60 minutes, although the sleep-deprived EEG takes longer. At the end of the study, the technician removes the electrodes using gauze and alcohol. This is an outpatient procedure with no side effects, so the patient can resume their routine normally. However, if a sedative has been administered, they may feel drowsy, so it is advisable to be accompanied and to rest at home.
Specialties that request the encephalogram
The electroencephalogram is requested in neurology consultations.
How to prepare
To facilitate the placement of the electrodes, the patient should come with clean hair free of cosmetic products such as conditioners, hairsprays, or gels. Caffeine or other stimulants should not be consumed in the 8 to 12 hours prior to the study, as they can affect electrical activity and interfere with the results. Likewise, the patient should inform the doctor if they are taking medications such as sedatives, tranquilizers, sleeping pills, or muscle relaxants, as it may be necessary to suspend them.
In some cases, depending on the study's objective, the patient must undergo the test without having slept the night before (sleep-deprived electroencephalogram).
