An electroencephalography machine or EEG records the electrical activity of the brain through the skull. The EEG machine is highly sensitive monitoring equipment designed to track electrical charges spreading through the brain and record brain wave patterns.
Types of EEG Tests
EEG investigations can include
- Routine EEG (20min)
- Ambulatory Video EEG Studies (>3 days)
- Sleep-Deprived EEG (>1 hour)
- Prolonged EEG (> 3 hours)
EEG findings vary depending on the activities during the study. For example, during sleep, the brain exhibits a different brain wave pattern compared to wakefulness.
Why has an EEG Been Recommended
EEG tests contribute to decision-making regarding the best medical management of certain conditions. EEG testing is used to:
- Help diagnose certain seizure disorders,
- Help understand brain tumours,
- Diagnose epilepsy and assess the types of seizures that are occurring as well as monitor epilepsy for ongoing management
- Classify seizure disorders or epilepsy (focal, generalised or focal with secondary generalisation).
- Understand brain activity before heart or liver transplantation.
- Evaluate brain activity after a severe head injury or brain damage from inflammation of the brain or spinal cord,
- Assist physicians in identifying causes of other problems such as sleep disorders and changes in behaviour, alcoholism,.
- Look for organic causes of psychiatric symptoms and disabilities in children, certain psychiatric disorders, and metabolic and degenerative disorders that affect the brain
- Monitor brain activity when a patient is fully anesthetised or loses consciousness
- Determine irreversible brain death or confirm brain death.
During an EEG Test
EEG tests are
- Non-invasive and pain-free
- Performed in a doctor's office at a testing facility by a trained EEG technician.
- Usually lasts 1 to 2 hours, and
- Normal activity can resume afterwards.
During the test, a patient’s principal role is to remain still, relaxed, and comfortable. Typically, patients lie on their backs with their eyes closed.
- The patient’s head is measured,
- Between 17 - 21 metal sensor plates (electrodes) are placed at measured intervals to the head (scalp). These electrodes are held on using a sticky paste.
- Alternatively, patients may have a cap containing electrodes fixed to their heads, which can be attached using tiny needles. Patients will feel a slight prick on their scalp.
- Wires (leads) then attach the electrodes to a computer and carry the electrical energy of the brain to a machine for reading.
- The computer measures and amplifies the brain’s electrical activity through the electrodes and records the electrical activity of a patient’s brain,
- A very low electrical current is sent through the electrodes, and the baseline brain energy is recorded.
- Further measurements are mapped, and the electrical activity changes alter the height of the wavy lines that are recorded.
- The series of wavy or jagged lines are recorded and may also be printed out on paper.
- Through an EEG, doctors can look for abnormal patterns that indicate seizures and other neurological problems,
- The neurologist interprets the mapped electrical activity.
The patient may be asked different things during the test to record the brain activity while the patient performs the task. Tasks can include hyperventilating, opening and closing the eyes rapidly a few times looking at a strobe light or being asked to sleep or being given a sedative.
Before an EEG
Your doctor will give you instructions to follow before undergoing an EEG test.
Common guidelines before having an EEG include:
- Must avoid prescription drugs that affect the nervous system 1-2 days before the test.
- Must avoid caffeine intake
- Avoid using hair styling products (hair spray or gel). It is important to keep the hair clean and free of sprays, oils, creams and lotions on the day of the test.
- If the patient undergoes a sleep EEG, he may be asked to stay awake the night before the test.
EEG Tests for Epilepsy
The brain also generates different wave patterns depending on the type of epileptic seizure.
The most informative pattern of change on routine EEGs, which occurs in between seizures, is called an epileptiform discharge. This is an abnormal buildup of electrical activity that typically occurs in the area of the brain, causing seizures.
Brain waves vary unpredictably in between seizures, and only 35-50 per cent of people with epileptic seizures will show a definitive epileptiform discharge on routine EEG studies.
Understanding these epileptiform patterns, along with a complete neurological exam and medical history, enables your doctor to determine the type of epilepsy and make recommendations for the best course of treatment.
EEG Risks
An Electroencephalogram (EEG) is a safe test as no electric currents are run through a patient’s body and very few risks.
If the patient has a seizure disorder such as epilepsy, the doctor may want to stimulate and record a seizure during the EEG.
A seizure can be triggered by flashing lights or a change in breathing patterns. There is a small risk of injury with initiating a seizure. Although every effort is made to educate you on electroencephalograms and take control.
