Illustration of a patient undergoing an EEG while the doctor observes.

Ultimate guide to the EEG test

What is an EEG test?

Electroencephalography (EEG) is a test that uses metal discs called electrodes placed on the scalp to record the electrical activity in the brain. It’s primarily used to test for epilepsy and disorders that affect the brain.

The electrodes detect the electrical impulses that brain cells use to communicate with one another. These impulses are recorded through the electrodes by a computer system, where they appear as a series of wavy lines (known as a trace), allowing scientists to read a snapshot of the brain activity.

For close to a century, EEG has been used and refined, leading to many discoveries in neurology and psychiatry, as well as helping doctors diagnose and treat their patients.

Child with EEG electrodes attached to her head

[Image description: A young patient undergoing an EEG, whereby multiple electrodes are attached to the head to record electrical brain signals.]


The benefits of EEG

In the broadest sense, EEG is used to study or monitor the activity of the brain. It has a variety of applications in medicine, such as helping study sleep disorders, seizure disorders, psychiatric conditions, and many other conditions.

Most commonly, it’s used for diagnosing brain disorders and monitoring how they affect the brain’s activity. It’s often used as a tool for diagnosing epilepsy and other causes of seizure activity and is helpful for monitoring these over time to assess the effectiveness of certain treatments. 

There’s a reason many neurologists and other medical professionals have come to rely on EEG tests. They’re precise, safe, relatively inexpensive, and non-invasive.

The history of EEG

Electroencephalography is nearly a century old. In 1929, German psychiatrist Hans Berger published his essay On The Electroencephalogram Of Man. In the essay, he demonstrated the method of recording the electrical activity from the brain.

He did this using a roughly constructed EEG machine that produced some of the signature wave patterns of lines that would be produced by today’s modern machines.

Hans Berger with an early EEG of his daughter's brain

[Image description: On the left, there are three sketches of brain electrical activity. On the right, there is an image of Hans Berger drawing these sketches.]


For many years, analog EEG machines used a stylus to record brainwave patterns using ink and paper. Today, recording is more commonly done with a digital system that records your brainwaves and displays them on a screen.

Modern EEG machines have excellent time resolution, meaning they can easily detect brainwave activity within millisecond timescales. They provide greater accessibility, adaptability, and improved analytical methods of tracking data.


Why are EEG tests done?

When a person presents behavior which could be caused by an issue with their brain activity — such as a seizure — it’s important to ensure that the correct cause is identified. EEG tests are used to give neurologists a look into the brain’s electrical activity, allowing them to detect abnormal features in the electrical impulses.

A trace of the brain activity is used to identify any irregularities through analysing patterns and shapes in the waves.

How brain activity appears as an EEG trace

[Image description: Screengrab of EEG data displaying electrical signals received during testing.]


Why do medical professionals recommend EEG?

When people have seizures or other events that are caused by an abnormality in the brain, EEG tests are often one of the first tests to be recommended. It is the primary diagnostic tool used if a doctor suspects a person has epilepsy.

An EEG can also be used to confirm if events are not caused by an abnormality in the brain, but rather by the heart. The test results can help doctors decide which steps to take in a treatment plan, or if further testing is needed.

Pros and cons of an EEG test


  • They are effective tools for making initial diagnoses based on irregular brain activity
  • They are relatively inexpensive, reliable, and safe
  • They are non-invasive, only requiring electrodes to be attached to the scalp


  • While EEG tests provide a good basis for other imaging, by itself it is not always enough to provide complete answers

How does an EEG work?

So, what exactly do little waves on a screen have to do with what’s happening in the brain? Well, it all starts with the billions of cells that are in the human brain. About half these cells are neurons while the other half help to facilitate the activity of neurons.

This is done through a series of gateways between the neurons called synapses, which are responsible for inhibiting or exciting neural activity.

Human brain and neurons in detail

[Image description: Illustration of a person with an illuminated brain. A section of the brain is magnified to show the numerous interconnected neurons sending electrical signals.]

During an EEG test, electrodes are attached to your scalp using a kind of removable glue. As your neurons are firing, their combined effect can be detected on the scalp by the electrodes.The brain waves are then amplified and recorded by a computer, creating a trace of brain activity.

What types of brain activity can EEG measure?

EEG has been used to study all kinds of cognitive processes like learning, memory, attention, sleep, emotions, and many others. Because the brain uses such vast networks of neurons for so many different processes, there are many activities that EEG can be used to study.

Doctors, including psychiatrists, are often most interested in the kinds of events that cause unusual brainwave activity. This includes symptoms like seizures, panic attacks, insomnia or sleep activity, strokes, headaches, dizziness, and many other behaviours related to specific brain disorders or medical conditions.

When should you get an EEG test?

When you experience an event related to unusual brain activity, such as a seizure, your doctor may recommend an EEG test to help determine the cause. This is often the case when there’s reason to believe that you may have a condition such as epilepsy, trauma, or other disorders of the brain.

If you’ve recently had a seizure, panic attack, severe migraines, or have recently fainted, then you should absolutely see a doctor to get their expert opinion. Ultimately, your doctor may or may not refer you for an EEG test depending on what information they need about your condition.

Common symptoms that qualify for EEG tests

There are a variety of events that EEG can be used to examine, and there are also a variety of seizure-like symptoms that may or may not be seizure related. In either case, these kinds of symptoms may warrant an EEG test to make an initial diagnosis.

Symptoms include: 

  • Seizures — These often present as fainting spells, blackouts or blank stares, jerking movements, funny turns, or déjà vu experiences. As there are many kinds of seizures, it can be difficult to distinguish between them and their specific causes without further investigation
  • Panic and anxiety attacks — Understanding your brainwave activity during these attacks may also help your doctor determine what triggers them and what kind of treatment is therefore suited to your individual needs
  • Insomnia and other sleep disorders — Your brain goes through several cycles of your sleep and events can occur during this time. Events can also be triggered by lack of sleep. Using an EEG to monitor your activity while you’re asleep or sleep deprived can help your doctor determine the cause of your events
  • Brain dysfunction and trauma — After a traumatic head injury or instances of cognitive dysfunction, EEG tests may be called for to assess the impact and extent of these issues
  • Others — Strokes, tumours, and inflammation in the brain alongside seizures or seizure-like events may lead to EEG tests in order to determine the extent of damage or to isolate the affected areas of the brain

If you have experienced any of these symptoms, you should have a conversation with your doctor to address your concerns. 

9 questions to ask your doctor if you think you’re having seizures. Download our “Preparing for your appointment” worksheet.

Illustration of person getting an EEG test performed by a medical professional

[Image description: Illustration of a patient wearing numerous electrodes on their head connected to a machine, which records the brain electrical activity. A doctor is smiling at the patient, while holding a tablet and wearing a stethoscope.]

Types of EEG tests

Routine EEG

Routine EEGs are typically performed in a clinical setting such as a doctor’s office or hospital. They typically last between 20-30 minutes, which is why they’re used only when a short study is necessary. They can be used to detect abnormal brain activity that may be the result of a condition such as epilepsy, but are less useful when seizure activity or other events require prolonged monitoring. It isn’t necessary to be having a seizure or any other related event at the time, as what’s important is monitoring the general activity of your brain.

Prolonged EEG

Prolonged EEG is similar to routine EEG, except the test lasts for 3 hours. It is also accompanied by seizure provocation methods — such as photic stimulation (lights flashing at different frequencies) and hyperventilation (deep breathing for a couple of minutes). It is sometimes recommended as a first test after a possible seizure-like event.

24-Hour EEG

As the name implies, these kinds of EEG tests occur over a 24-hour time span. They are often performed in a hospital usually with video recording. These tests are much more useful for observing seizure activity directly if there’s reason to suspect that one might occur within that time.

Long-term EEG

In some cases, even a 24-hour window is not enough time to observe the kind of activity needed to make a diagnosis. In these cases, the test may last anywhere from three days to as long as 10 days. Long-term EEG tests can be performed in a hospital or at home with video recording. The goal is to allow a long enough window of time to record the suspected event. Long-term EEG tests are, generally speaking the longest, and therefore, the most likely to record an event — providing higher diagnostic utility.

Ambulatory EEG

An ambulatory EEG is an EEG test that allows a person to walk and move freely. Ambulatory means the person is mobile, as a portable EEG device is worn on the body and not tethered to a fixed machine. Typically, 24-hour and prolonged EEGs can be performed as ambulatory EEG. This type of testing can be done in the home or at the hospital.

Sleep-deprived EEG

Sleep-deprived EEGs are used to study brain activity associated with insomnia, sleep disorders, and other issues. Lack of sleep is known to be a trigger for seizures in some people, so this type of EEG is done to increase the likelihood of capturing an event during monitoring.

What makes Seer Medical’s EEG test different from others?

At Seer Medical, we provide at-home video-EEG-ECG. The test is:

  • At-home — the test is completed at home with no hospital visits
  • Long-term — the duration of the test can be between 3 to 10 days, depending on what your doctor recommends
  • Ambulatory — you wear a portable EEG-ECG device and are able to move about freely in your home

By extending the monitoring period for 3-10 days, there is a higher chance of capturing an event if it occurs. Being in the home with the ability to move freely exposes you to your natural environment and possible event triggers. 

Our EEG test is done together with an electrocardiogram (ECG or EKG) so that your doctor can determine if the events you are experiencing are coming from your brain or your heart, or possibly even both. Heart conditions can sometimes be confused with brain conditions because symptoms can look similar. This is why ECG is so important for understanding what is really going on. Many peoples’ diagnoses have changed after their ECG results revealed that they don’t have epilepsy at all.

Seer Medical’s monitoring also includes video, which captures what your body does during an event. There are many different types of seizures associated with different types of epilepsy. Most seizures are nothing like the ones you may have seen depicted in the movies. Some seizures involve no more than staring absently for a few seconds. If you experience any kind of seizure, the video will help to classify the type and guide the right treatment plan. 


Q: What does an EEG test detect?

A: The EEG test detects electrical activity in the brain caused by groups of firing neurons. This electrical activity creates a signal, known as a brainwave, that EEG machines detect and record.

Q: Is EEG painful?

A: EEG tests are relatively simple, non-invasive, safe, and for most people completely pain-free.

Q: Are there any risks or side effects?

A: There is a chance of skin irritation around the places where the electrodes are stuck to the body as a result of collodion adhesive. Any irritation should clear up and heal quickly after monitoring. To read more about collodion, click here.

Q: Do I need to shave my head for an EEG test?

A: No. You may have heard that you’ll need to shave your head before an EEG, but this is not at all necessary nor recommended. Even if your hair is thick and long, the electrodes will have no trouble picking up your brainwaves.

Q: Is EEG better than an MRI?

A: EEG and MRI (magnetic resonance imaging) are completely different tests. It depends on the specific symptoms or condition you have. EEG is used primarily to look for abnormalities in brain activity, whereas MRI is used to look for structural or anatomical abnormalities in the brain. Your doctor might recommend you do neither, one, or both depending on the information they have about your medical history.