Electroencephalogram or EEG Test Information

An EEG, or electroencephalogram, is the measure of the ‘electrical activity’ in the brain. It is a non-invasive and pain free test. Sensitive monitoring equipment records the activity through electrodes placed on the patient’s scalp. The EEG is primarily used, but not limited to, the evaluation and diagnosis of epilepsy. Patients who experience an; altered state of consciousness, loss of consciousness, change in behaviour, panic attacks, unusual movement, visual hallucinations, auditory hallucinations, drop attacks, fainting episodes, and altered sensations may be referred for investigation via an EEG to determine if the symptoms are due to ‘abnormal electrical activity’.

Routinely the EEG will comprise of several components including:

  1. A Resting Phase – approximately 10 mins where the patient will rest quietly;
  2. Hyperventilation – the patient will be asked to breath deep and heavy for 3-5 minutes;
  3. Photic Stimulation – the patient will be showed some flashing lights for approximately 3 minutes.

Hyperventilation induces diffuse and paroxysmal slowing, due to the cerebral vasoconstriction, which may manifest clinically as an absence seizure depicted by the presence of 3Hz spike and slow wave complexes on the EEG. In other words, breathing deep and heavy changes the blood flow in the brain. For patients with a specific type of epilepsy this may induce an ‘absence’ seizure, also known as ‘petit mal’ seizures. During this brief seizure, the patient will appear vacant or vague and may have flickering eye movements or other discrete movements. This can often go unnoticed.

Photic stimulation is significant for the detection of photosensitivity for certain patients. The contrast between the flickering light stages may induce discharges such as spike and slow wave complexes, polyspike, spike or sharp wave discharges. These discharges mainly occur in the occipital regions during this provocative manouevre and can be used in the diagnosis of epilepsy. In other words, the flickering light can cause epileptic discharges in the region that is used for visual processing.

Downloadable Referral & Test Information

Preparation for an EEG

  • Wash and thoroughly dry your hair the evening before your appointment and ensure that your hair is free of hair styling products (mousse, gel, hair spray, etc.).
  • Follow your normal medication routine (unless instructed otherwise by your doctor).

Sleep Deprived EEG

A sleep deprived EEG may be performed to provide additional information, particularly if the routine EEG is normal. Patients undergoing a sleep deprived EEG will be asked to:

  • Adjust your sleep schedule the evening prior to your EEG procedure (for example, midnight to 4:00 am) or try to sleep 2-3 hours less than normal (this will aid in inducing sleep at the time of your EEG).
  • Avoid consuming any caffeine for a minimum of 12 hours before to your appointment.
  • Take your medications as normal.

Frequently asked EEG questions

How long does the test take?

Generally the appointment takes one hour. This allows for a general discussion about the test, 10-15 minutes to attach the leads, followed by a 20-40 minute recording.

Is there any preparation for the test?

No preparation required (unless it’s a sleep deprived EEG - in which case, see above information). No fasting required.

Do I still take my medications?

YES continue all regular medications. We do not recommend ceasing medications prior to the EEG *unless advised and consulted by a specialist.

Will I be able to drive after the test?

Yes, you will be able to drive after the test, unless it’s a sleep deprived EEG.

Will I have a seizure during the test?

No, not necessarily. Don’t worry, we do not try to bring out a ‘convulsion’ during an EEG. During the EEG we use provocation manouevres; hyperventilation & photic stimulation. These are both done during an EEG to ‘bring out epileptiform activity on the EEG ’. Hyperventilation may bring out absence seizures. Photic stimulation is used to bring out photosensitive epilepsy (seen in idiopathic generalized epilepsy) and only a small percentage of people will react to the lights. If a reaction is seen on the EEG (which can be seen before a seizure starts) then the lights are STOPPED.

Are there any after affects of the test?

No, there are no after affects or complications of the test.

My child is coming for an EEG and are very active, how will the test be done?

“We get what we can”. Kids can be difficult to obtain an EEG, particularly around 2-3 years of age. Persistence is the key. We recommend bringing any entertainment possible, whether it be an adult family member/friend, ipad, ipod or toys. Every effort is made to get the electrodes on to obtain some sort of recording. The EEG may be performed on a chair (rather than a bed) or the lap of an adult (parent or care giver).


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