Gina Johnson
Electroencephalography, or EEG, is a widely used tool for measuring brain activity during sleep. It involves placing electrodes on the scalp to detect electrical signals produced by the brain. These signals are then recorded and interpreted by a doctor. EEG is used to study brain activity during different behavioural states, including sleep, and is also employed in the diagnosis of neurological conditions such as epilepsy and sleep disorders. In addition to EEG, other tools such as polysomnography (PSG) and functional magnetic resonance imaging (fMRI) are also used to study sleep and brain activity during sleep.
| Characteristics | Values |
|---|---|
| Name of tool | Electroencephalogram (EEG) |
| What it measures | Brain rhythms, or patterns of brain activity |
| How it works | Electrodes are placed on the scalp to detect and record electrical activity produced by the brain |
| Who performs it | A highly trained specialist called a clinical neurophysiologist |
| Where it's performed | During a short visit to the hospital or at home |
| How long it takes | 45 minutes to 2 hours |
| How it feels | Painless and comfortable |
| Safety | Very safe |
| Preparation | May be asked to stay awake or sleep-deprived the night before the test |
| Variants | Sleep-deprived EEG, ambulatory EEG, video telemetry EEG, prenatal EEG, neonatal EEG |
| Use cases | Diagnosing and monitoring conditions affecting the brain, including epilepsy, sleep disorders, depth of anesthesia, encephalopathies, cerebral hypoxia, brain death, Alzheimer's, certain psychoses, and narcolepsy |
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What You'll Learn
Electroencephalogram (EEG)
EEG is used to help diagnose and monitor various conditions affecting the brain, such as epilepsy and seizures. It can also be used to detect sleep disorders, depth of anaesthesia, coma, encephalopathies, cerebral hypoxia after cardiac arrest, and brain death. The test can be performed while the patient is awake or asleep, depending on the condition being evaluated. In some cases, patients may be asked to stay awake the night before the test to ensure they can sleep during the procedure.
EEG can also be used to determine the overall electrical activity of the brain, such as in cases of trauma, drug intoxication, or brain damage. It is often used to evaluate brain disorders and can detect seizure activity, lesions, and slow brain waves associated with conditions like Alzheimer's disease, psychoses, and narcolepsy. The readings depict differences in both amplitude and frequency over time, with increases in amplitude indicating higher synchronous activity of cortical neurons.
EEG technology has been advancing since 1924, and in the 1950s, William Grey Walter developed EEG topography, which allowed for the mapping of electrical activity across the brain. This technique has been used in various fields, including space exploration and robotics. Despite the development of other imaging techniques like MRI and CT scans, EEG remains a valuable tool due to its mobility and millisecond-range temporal resolution capabilities.
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Evoked potentials (EP)
Electroencephalography (EEG) is a test that involves attaching small sensors to the scalp to record brain activity. Evoked potentials (EPs), also known as evoked responses, are a type of EEG that measure the electrophysiological responses of the nervous system to various stimuli. EPs can be used to assess the central nervous system's (CNS) arousal or activation level during sleep.
EPs are small amplitude changes in the EEG that occur due to an external physical or internal psychological stimulus. They provide valuable data that can complement routine EEG and behavioural measures, such as reaction time. EPs offer insights into signal processing that may be independent of factors like motor control, motivation, and conscious awareness of presented stimuli.
Visual evoked potentials (VEPs) are a commonly used type of EP. They include flash and checkerboard types and are used to test the function of the visual pathway from the retina to the occipital cortex. The typical waveform involves an initial negative peak, followed by a large positive peak, and then another negative peak.
Short-latency somatosensory evoked potentials (SEPs) are another type of EP. They are believed to be generated by volleys traversing the large-fiber sensory system, specifically the posterior columns and medial lemnisci. SEPs have shown potential in predicting outcomes after postanoxic coma and may find wider clinical applications in the future.
In the context of sleep research, N350 is an important measure of the onset of drowsiness during NREM sleep. It may indicate the activation of a sleep-specific inhibitory mechanism that leads to vertex sharp waves and possibly K-complexes. N550, on the other hand, is a marker of EEG delta generation capability and provides a functional assessment of CNS structural integrity.
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Video telemetry/video EEG
Video telemetry, also known as video EEG, is a special type of electroencephalogram (EEG) that involves recording a person's brain activity on video while simultaneously capturing EEG data. This combination of video and EEG recordings helps to accurately classify seizure types and localise seizure foci in the brain, which is crucial for determining the suitability of surgical treatment.
During a video EEG, electrodes are attached to the scalp with glue to record the brain's electrical activity. The glue is dried using bursts of air from a small air compressor, which can be loud but is painless. Simultaneously, a camera continuously records the individual, capturing any physical symptoms, behavioural changes, or movements that may be associated with seizure activity. This allows doctors to compare what happens physically during a seizure with the corresponding EEG recording, aiding in the classification of seizure types.
Video EEG tests are typically conducted in a hospital setting, as seizures can be unpredictable and require monitoring in a safe environment. In some cases, seizure medications may be adjusted to provoke seizures and capture them on video and EEG. This helps identify seizure triggers and understand their frequency. The length of testing varies depending on the individual's seizure patterns, seizure type, and the specific monitoring objectives.
Video telemetry is particularly useful when standard EEGs do not provide sufficient information on the source and progression of seizures. By allowing prolonged monitoring, video EEGs can capture multiple seizure events, helping to identify whether seizures originate from a single area or multiple areas of the brain. This information is critical for determining the success rate of potential surgical interventions.
Video EEGs are commonly used to better understand and diagnose epilepsy in children. Parents or caregivers play an important role in identifying typical events or seizures, and their presence can help ensure the child's comfort and safety during testing. The combination of telemetry and video recordings provides a comprehensive view of brain activity and physical symptoms, aiding in the accurate diagnosis and treatment planning for epilepsy.
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Sleep-deprived EEG
Electroencephalography, or EEG, is a widely used method for measuring brain activity during sleep. It is a painless and non-invasive test that involves placing electrodes on the scalp to record electrical activity in the brain. A sleep-deprived EEG is a variation of a standard EEG test and is often used to detect subtle seizures or epilepsy.
During a sleep-deprived EEG, patients are instructed to obtain significantly less sleep than usual, typically four hours less, before the test. The test itself is similar to a regular EEG, with electrodes attached to the scalp to record brain activity. However, the sleep-deprived EEG procedure usually takes longer, often a few hours, to ensure that the patient falls asleep or dozes during the test. The recording continues while the patient sleeps, capturing brain activity during this state.
A sleep-deprived EEG is often recommended when a standard EEG fails to show any unusual electrical activity in patients with suspected seizures or epilepsy. Sleep deprivation can improve the accuracy of epilepsy diagnoses and increase the likelihood of detecting characteristic electrical patterns known as epileptiform discharges. The test can also help differentiate various types of epilepsies and seizures, as well as identify abnormalities associated with seizures in some psychiatric presentations.
It is important to note that the sleep-deprived EEG is a safe and painless procedure. Patients are carefully monitored throughout the test, and in the event of a seizure, fast-acting anti-seizure medication is administered immediately. Patients may feel tired after the test, especially if they have undergone sleep deprivation, so it is recommended to have someone pick them up from the hospital.
The results of a sleep-deprived EEG are typically analysed by a neurologist or a clinical neurophysiologist, who compares the recorded brain waves to what is considered normal for the patient's age. This analysis helps in diagnosing and monitoring various brain disorders, particularly epilepsy and seizure disorders.
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Ambulatory EEG
An ambulatory electroencephalogram (EEG) is a test that can be carried out at home to record brain activity over a longer period, typically a number of hours or days. It is used when a longer recording is required to capture abnormal brain activity that could not be recorded with a regular 20-minute EEG. This may be the case if abnormal activity only happens a few times a day or during certain times of the day. An ambulatory EEG can increase the chance of recording an event or abnormal changes in brain wave patterns.
During an ambulatory EEG, small sensors or electrodes are attached to the scalp to pick up the electrical signals produced by the brain. These electrodes are connected to a small, portable EEG recorder, which can be worn on the waist or clipped to clothing. The recorder is slightly larger than a portable cassette player and is connected to the electrodes by wires that can be placed under or outside the shirt. The patient can then go about their daily activities, although they will need to avoid getting the equipment wet.
The electrodes used in an ambulatory EEG need to stay in place for longer than a regular EEG, so a special glue called collodion is typically used to keep them in place. After the test, the glue can be removed with acetone or a similar solution. Most recorders have an event" button that patients can press if they experience any seizures or unusual symptoms, marking the time on the EEG recording. This allows doctors to compare the patient's reported experiences with the corresponding EEG data.
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Frequently asked questions
Electroencephalography (EEG) is a tool used to measure brain activity during sleep.
An electroencephalogram (EEG) is a recording of brain activity. During this painless test, small sensors are attached to the scalp to pick up the electrical signals produced by the brain.
An EEG detects the general activity of the cortex by measuring small (~10 uV) fluctuations in voltage. This technique does not measure the electrical activity of a single neuron, but rather measures the electrical activity of a large population of neurons, generating a signal that is large enough to detect.
