A polysomnography (PSG) and an electroencephalogram (EEG) are two tests that can provide important information about brain activity and sleep. Although they are different tests, they can be used together to identify abnormal brain activity, sleep disorders, and certain neurological conditions.
EEGs help doctors evaluate brain conditions such as brain tumors, traumatic brain injuries, stroke, Alzheimer’s disease, dementia, and encephalitis. EEG can show changes in electrical brain activity associated with these conditions.
One of the most important uses of an EEG is detecting epilepsy and seizures. Abnormal bursts or spikes in brain activity can indicate where seizures originate. Longer-term or video EEG monitoring can be especially useful because it may capture the brain activity occurring during an actual seizure. However, a normal EEG does not completely rule out epilepsy because a seizure may not occur during the test.
EEGs may also show abnormal brain-wave patterns following a head injury, stroke, or brain tumor. They can provide information about how the brain is functioning, while other tests such as CT or MRI are generally used to examine the brain’s physical structures. EEG can also show abnormal patterns associated with some forms of dementia and Alzheimer’s disease.
Importantly, a sleep study that includes an EEG can help identify seizures that occur during sleep. These seizures can sometimes look like other sleep disorders, so recording brain activity at the same time as body movements and breathing can help distinguish epilepsy from conditions such as sleep apnea or REM sleep behavior disorder.
In comparison, a polysomnography (PSG), also known as a sleep study, is a diagnostic test which examines how different body systems work while a person is asleep, and then records the corresponding results. During a polysomnography, sensors monitor brain waves, eye movements, heart rate, breathing, blood oxygen, body position, and limb movements.
Sleep studies identify conditions such as sleep apnea, narcolepsy, periodic limb movement disorders, and certain parasomnias. Finding the specific disorder helps doctors choose the appropriate treatment rather than relying on guesswork.
The EEG portion of the sleep study helps determine the different stages of sleep and whether normal sleep patterns are being disrupted. This provides health care providers a comprehensive synopsis of the quality of sleep a patient is receiving which allows them to diagnose or dismiss certain health issues.
Sleep studies are particularly useful for identifying sleep apnea and other sleep-related breathing disorders. They can show abnormal breathing patterns and drops in blood oxygen during sleep. A sleep study can also identify periodic limb movement disorder, which involves repeated leg movements that interrupt sleep.
Another condition that can be evaluated through a sleep study is narcolepsy. People with narcolepsy may fall asleep very quickly and enter REM sleep abnormally early. A sleep study followed by a Multiple Sleep Latency Test (MSLT) can help doctors evaluate these abnormal sleep patterns.
Sleep studies can also identify REM sleep behavior disorder (RBD). A person who experiences RBD may physically act out dreams because the normal muscle paralysis associated with REM sleep does not occur properly. The study can record abnormal movements and other activity during REM sleep.
Once the results are interpreted and these conditions are identified, sleep specialists can recommend treatment based on the patient’s specific condition. Treatments may include CPAP, oral appliances, medication, lifestyle changes, cognitive behavioral therapy, or light therapy.
Treating the underlying sleep disorder can lead to more restorative sleep, increased energy and alertness, better mood, and improved concentration and cognitive function. Untreated sleep disorders can contribute to problems such as high blood pressure, heart disease, diabetes, and stroke. Diagnosing and treating the disorder can therefore benefit both sleep and overall health.
Sleep studies can also be used to evaluate treatments and determine whether adjustments are needed. For example, a patient’s CPAP settings may be adjusted based on the results, and follow-up testing can help track progress.
A hypnogram is a graph that shows how a person moves through the different stages of sleep over the course of a night. It is created from information collected during the sleep study, sensors collect information from EEG (brain waves), EOG (eye movements), and EMG (muscle activity).
The night’s recording is divided into 30-second epochs. Each epoch is examined to determine what stage of sleep the patient is experiencing.
Once each 30-second epoch has been scored, the sequence of sleep stages is placed onto a graph. Time is displayed along the horizontal axis, while the different sleep stages are displayed on the vertical axis. Connecting the scored stages produces the hypnogram, allowing the entire night’s sleep pattern to be seen visually.
The hypnogram can also be analyzed beyond simply looking at how much time was spent in each stage. Researchers can examine how frequently and how quickly a person transitions between wake, NREM, and REM sleep. This can reveal sleep fragmentation that might not be obvious from total sleep-stage percentages alone.
A person repeatedly transitions between NREM and REM sleep, with periods of wakefulness occurring throughout the night. The hypnogram makes these transitions and the amount of time spent in each stage easy to visualize.
Hypnograms make it easier to visualize sleep patterns and transitions throughout the night. They can help healthcare providers and researchers identify sleep fragmentation, abnormal sleep architecture, and disruptions in normal sleep cycles.
A sleep study can identify abnormal breathing patterns and drops in blood oxygen during sleep. The results can help healthcare providers determine whether a patient has sleep apnea and guide treatment, such as adjusting CPAP settings.
Yes. Follow-up sleep studies can help healthcare providers determine whether a treatment is working and whether adjustments are needed. For example, sleep-study results may be used to help adjust CPAP settings and monitor a patient’s progress.
A sleep study can identify abnormal breathing patterns and drops in blood oxygen during sleep. The results can help healthcare providers determine whether a patient has sleep apnea and guide treatment, such as adjusting CPAP settings.
Overall, an EEG is primarily focused on electrical activity in the brain, while a sleep study evaluates brain activity along with breathing, oxygen levels, heart rate, eye movements, and muscle activity during sleep. EEG is especially important for detecting epilepsy and seizures, but it can also provide information about brain injuries, stroke, tumors, dementia, Alzheimer’s disease, and other neurological problems.
Polysomnography is mainly used to diagnose sleep apnea, narcolepsy, periodic limb movement disorder, REM sleep behavior disorder, insomnia, and other sleep-related conditions. When an EEG is included with a sleep study, it can also help identify seizures occurring during sleep.
Sleep-study results give healthcare providers objective information about what is happening in a patient’s body during sleep. This information helps them find the cause of poor sleep, select an appropriate treatment, and monitor its effectiveness. As a result, patients can experience better-quality sleep, improved daytime alertness and mood, and potentially better long-term health.
A hypnogram turns the detailed data collected during a sleep study into an easy-to-understand picture of how sleep progresses throughout the night. This makes it an important tool for evaluating sleep quality, identifying abnormal sleep architecture, and understanding how sleep disorders affect a patient’s sleep.
Electroneurodiagnostic technologists work with specialized testing and monitoring technologies that record electrical and physiological activity from the brain and nervous system, including EEG and sleep-related monitoring.
Midwestern Career College’s Electroneurodiagnostic (END) Technology program prepares students for entry-level roles while developing foundational skills in neurological testing, patient care, and the use of specialized diagnostic equipment.
This article was developed using guidance and educational resources from the following medical and clinical organizations:
Arthur Bagdasaryan is Content Creation & Editorial Specialist at Midwestern Career College. He develops informative, accessible content designed to help readers better understand career-focused education, healthcare topics, and the professional landscape.
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