Electroencephalogram – EEG


Last Updated December 20th, 2021

What is an EEG?

An electroencephalogram or EEG test is a process that is used to study the electrical activity in the brain and point out any anomalies. The brain consists of a dense network of cells and half of them are neurons, which are interconnected through synapses. These neurons generate electrical impulses, called synaptic activity, for communication.

When thousands of neurons work together, the signal can be tracked and measured even at the outer surface of the brain. EEG uses electrodes mounted on the scalp to measure the synaptic transmissions.

What is the working principle of an EEG?

The electrodes measure the voltage fluctuations and the data is digitized and sent to an amplifier. The data finally shows up as wavy lines on a computer screen. The unit also uses filters that remove the frequencies of higher and lower ranges so that the important range (1–30 Hz) can be captured effectively.

The area of the cortex that is responsible for processing the information can be determined from the data. This method is one of the simplest tools to diagnose epilepsy, seizures and other disorders related to the brain. It is also used to detect abnormal brain waves in cases of coma, tumors, stroke, memory lapses or weakening of specific parts of the body.

What is the burden of neurological diseases in India?

The crude prevalence of neurological disorders in India lies close to 2400 cases per 100000 people in the general population, with higher prevalence observed in the rural demography as compared to the urban crowd. As per 2018 statistics, there are more than 30 million cases of neurological disorders reported in India.

Why do I need to undergo an EEG?

The EEG is mainly used to study the details of brain activity in the following conditions in a patient.

– Cases related to brain tumors.
– Any brain damage resulting from injuries.
– Inflammation in the brain resulting from encephalitis.
Dementia or mental confusion.
– Sleep disorders like obstructive sleep apnea.
– Diseases that result in brain degeneration.
– Disorders and infections that can cause metabolic disturbances which affect brain function.
– Hormonal conditions that might affect the brain tissue.
– Patients who are in the state of coma.
– Determine brain activity after a major surgery like a heart or a liver transplant.

EEG is often used to determine brain death for patients who are in a life support system. It is also used to study the brain functions during brain surgery. For those who are placed in a medically induced coma, EEG is used to study the right level of anesthesia.

How is an EEG performed?

EEG is a very safe and non-invasive test that does not cause any pain or discomfort. The electrodes do not transmit any sensation but just record the brain waves. The process can be conducted in various ways and some of them are described below.

Standard EEG– This is the normal process that is conducted and lasts for about 30 to 40 minutes. The amount of sleep, food, drink, and medications needed for this test is specified by the doctor.

Sleep EEG– In this case, the patient will be placed in a relaxed ambiance and will be asked to fall asleep. The electrodes will measure the data from the brain while the patient remains asleep.

Ambulatory EEG– In this process, a portable EEG recorder is tied around the waist through a belt and it records the brain waves continuously for days or weeks. The daily activities and drug dosages are also tracked so that the doctor can compare and study the pattern in detail.

Video EEG- These are used for patients suffering from seizures and are used only in hospitals. The patient is tracked by EEG and a video camera so that both the brain activity and the physical behavior can be monitored simultaneously.

EEG is conducted by specialized technicians and the following steps are involved during the process.

– You will be asked to lie down in a bed or an inclined chair.

– The technician will mark some points on your head where the electrodes will be placed. A special cream will be applied on the spots to improve conduction so that a high-quality reading can be obtained.

– Multiple electrodes will be attached to the spots on your head with the help of an adhesive. The electrodes are flat, metals discs and they generally vary between 16 and 30 in number.

– The electrodes gather the impulses from the brain which are continuously recorded. Each electrode has a number and also marked by a letter, depending on the area of the brain from where they are collecting information.

– The room is generally kept dark and the technician can ask you to perform certain activities like blinking the eyes, breathing deeply or look at some flashing lights.

– Once the procedure is over, the electrodes will be removed and you can leave the center unless the doctor advises something else.

– While the actual test can take anywhere between 30 to 40 minutes, the total time including the preparations can make it last for 1.5 to 2 hours.

What is the price for an EEG in India? 

The EEG test can cost anywhere between Rs 800 to Rs 3000 depending on the location and the qualities of the machinery used.

When will I get the test results?

The reports are usually delivered within 48 hours of the test.

What is the normal range for an EEG?

The EEG results show up in ‘peaks and valleys’ which can show a regular pattern when there are no abnormalities. The patterns are also classified into different types of brain waves, namely delta, theta, alpha, etc., depending on their frequency. In case the patterns show distinct or abrupt variations, some abnormality is suspected by the doctor.

In case a seizure happens during an EEG, the normal pattern of the waves is disrupted, resulting in different brain activity. The trained neurologist will study these wave patterns to determine the issues within the brain.

What do the results mean?

An abnormal EEG test can indicate that there is something wrong with a particular area in the brain. While the result may not pinpoint the cause, it is the first step towards the right diagnosis. Normal brain has a specific wave pattern that can be easily recognized by trained eyes. The frequent appearance of sharp spikes in specific areas may indicate areas of seizure near to that location.

The neurologist will determine as to what the abnormal readings indicate. While a normal EEG does not mean that there is no epilepsy and it is also possible to have an abnormal EEG and still not be affected by epilepsy. The doctor who ordered the report will analyze and discuss the details with you. Further tests like MRI or CT scans can be ordered if necessary.

Do I need to fast for the EEG?

Fasting is not required during the test as low blood sugar levels may influence the test results.

What else do I need to know before I appear for an EEG?

The following steps are to be kept in mind before appearing for the EEG test.

– You can wash your hair the night before the test and make sure not to apply any gels or haircare products.

– If you are taking any medications, discuss the same with the doctor and stop taking it if so advised.

– Avoid consuming any caffeine for at least eight hours before the test.

– If you are undergoing a sleep EEG, the doctor might ask you to sleep as little as possible the night before the test.

– The test does not have any side effects apart from giving you messy hair or generating some amount of tiredness. You will need to wash your hair thoroughly to remove any traces of the gel or cream used.

– If you have epilepsy, you may have a seizure during the test. Since the test will be closely monitored, you will receive help as soon as it happens.

– You can continue with your regular activities after the test unless you were sedated during it. In such a scenario you will need help to return home and not perform critical activities unless the sedative wears off.

Can pregnant women undergo an EEG?

Pregnant women can undergo an EEG test as it does not have any side effects on the fetus.

Is the EEG test possible for new-born babies?

EEG can be conducted on new-born babies in is an invaluable tool for checking brain activity in infants and detect any abnormal neural activity early on.

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