What is an EEG Test?
Key Findings
An EEG records brain wave patterns through small sensors placed on the scalp. Doctors use it to diagnose seizures, monitor sleep stages, detect abnormal activity, and study how the brain responds to stimulation. It does not involve electricity being sent into the brain, and it is completely non-invasive.
What Is Electroencephalography (EEG)?
An EEG, short for electroencephalogram, is a test that measures electrical activity in the brain. It is one of the most widely used tools in neurology because it offers a clear look at how the brain communicates, reacts, and functions in real time.
EEGs help diagnose conditions such as epilepsy, sleep disorders, head injuries, and unexplained episodes of confusion or fainting. The test is safe, painless, and suitable for people of all ages, making it an essential part of modern brain health assessment.
How an EEG Works
Every thought, movement, and sensation you experience begins with tiny electrical signals between brain cells. These signals create rhythms known as brain waves. An EEG detects these rhythms by capturing the electrical activity that reaches the scalp. The test uses electrodes attached with gel or adhesive, and these sensors pick up changes in voltage that occur naturally within the brain.
The result is a series of wave patterns displayed as lines on a screen. Different brain waves have different shapes and speeds. For example, slower waves appear during deep sleep, while faster waves appear when you are alert and concentrating.
By interpreting these patterns, specialists can understand how well the brain is functioning or whether something unusual is happening.
What an EEG Can Show
EEGs provide a detailed picture of how the brain behaves over time. They are especially useful for spotting irregular patterns that might indicate medical conditions.
One of the most common uses for an EEG is diagnosing epilepsy. Seizures leave distinct electrical signatures that the test can capture even when the person is not actively having a seizure. EEGs can also detect abnormal activity caused by infections, tumours, or metabolic problems.
In sleep medicine, EEGs help map the stages of sleep, including the transitions between light sleep, deep sleep, and REM sleep.
These recordings allow doctors to diagnose conditions such as narcolepsy or sleep-related movement disorders. EEGs can also show how the brain responds to stimuli, such as light or sound, which helps assess sensory processing.
Sometimes an EEG is combined with video monitoring for several hours or even days. This approach helps doctors match changes in electrical activity with noticeable behaviours or episodes.
What Happens During an EEG
The procedure is straightforward. You will sit or lie comfortably while a technician places a series of small metal discs on your scalp. These sensors are connected to a computer that records your brain waves. You may be asked to rest quietly with your eyes closed, open your eyes, breathe deeply, or look at flashing lights. These activities help reveal how the brain responds to different stimuli.
A typical EEG lasts 20 to 40 minutes, although longer recordings may be done if doctors are looking for specific events, such as seizures or sleep patterns.
None of the sensors send electricity into your body. They only record what your brain is already producing, so the test is entirely painless.
After the test, the sensors are removed and most of the gel washes out easily. A neurologist then interprets the results and compares the wave patterns to what is expected for your age and condition.
Why Doctors Order an EEG
Doctors use EEGs when they need clarity on how the brain is functioning beyond what imaging tests such as MRI or CT scans can provide. While structural scans show what the brain looks like, EEGs show what the brain is doing.
Some common reasons for ordering an EEG include:
Seizures or unexplained blackouts
Sudden confusion or memory problems
Sleep disorders or unusual sleep behaviours
Monitoring brain activity after injury or stroke
Investigating developmental or behavioural concerns
In many cases, an EEG can guide treatment decisions, track progress, or rule out serious conditions.
Are EEGs Safe?
EEGs are among the safest medical tests available. They do not use radiation, electricity, or invasive tools. The electrodes rest on the surface of the scalp and cannot cause harm. Even newborn babies and medically fragile patients can undergo EEG testing without risk.
The only time an EEG may feel uncomfortable is if flashing lights trigger symptoms in people with photosensitive epilepsy. This possibility is monitored closely, and the test can be adjusted as needed.
Final Thoughts: EEG Explained
An EEG is a powerful, non-invasive tool that allows doctors to see the brain in action. It helps diagnose seizures, understand sleep patterns, investigate neurological symptoms, and guide effective treatment.
Because it is simple, safe, and highly informative, the EEG remains a core part of neurological care and one of the best ways to understand how the brain communicates and responds.
Article FAQ
Can an EEG detect a brain tumour?
An EEG cannot directly detect a brain tumour, because it shows electrical activity rather than physical structures. Tumours are found through imaging tests such as MRI or CT scans. However, an EEG can sometimes reveal abnormal brain wave patterns that suggest the brain is being irritated or disrupted, which may prompt further investigation with imaging.
Can an EEG detect dementia?
An EEG cannot diagnose dementia on its own, but it can show patterns that support a diagnosis or rule out other neurological conditions. Some forms of dementia, such as Creutzfeldt-Jakob disease, produce distinct electrical changes. In most cases, doctors use EEG results together with memory tests, examinations, and imaging studies to form a clearer picture.
How is an EEG test performed?
During an EEG, a technician places small sensors on your scalp using gel or a mild adhesive. These sensors record the electrical activity produced by your brain. You may be asked to rest quietly, open and close your eyes, breathe deeply, or look at flashing lights while the machine records. The test is painless and usually lasts 20 to 40 minutes, although longer studies may be done when doctors need more information.
Who performs an EEG?
A trained EEG technologist or neurodiagnostic technician performs the test. After recording is complete, the results are interpreted by a neurologist or a specialist in clinical neurophysiology. These professionals are trained to analyse brain wave patterns and identify signs of abnormal activity.
Can an EEG detect anxiety?
An EEG cannot diagnose anxiety, but it can show patterns related to stress, such as increased high-frequency activity. These findings are not specific to anxiety, so doctors do not rely on EEGs for diagnosis. Instead, the test may be used to rule out neurological causes of symptoms.
Is EEG better than an MRI?
Neither test is better in a general sense, because they provide different types of information. An MRI shows detailed images of brain structures, while an EEG shows how the brain functions electrically. Doctors often use both when investigating seizures, unexplained symptoms, or neurological disorders to get a complete understanding of what is happening.
