We study sleep primarily using a combination of physiological measurements taken during sleep, collectively known as polysomnography. These measurements allow us to identify different sleep stages and detect sleep disorders.
Here's a breakdown of the common techniques used:
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Electroencephalography (EEG): This is the cornerstone of sleep studies. EEG uses electrodes placed on the scalp to measure brain wave activity. Different brainwave patterns correspond to different sleep stages (e.g., alpha waves during relaxed wakefulness, theta waves and sleep spindles during stage 2 sleep, and delta waves during deep sleep). EEG is crucial for identifying sleep stages and detecting abnormalities like seizures.
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Electrooculogram (EOG): This technique measures eye movements. Electrodes placed near the eyes record the electrical potential generated by eye movements. EOG is particularly important for identifying REM (Rapid Eye Movement) sleep, which is characterized by rapid, jerky eye movements.
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Electromyography (EMG): EMG measures muscle activity. Electrodes are typically placed on the chin or legs to monitor muscle tone. Muscle activity decreases during sleep, particularly during REM sleep, where muscle paralysis occurs. Monitoring muscle activity can help diagnose conditions like restless legs syndrome or REM sleep behavior disorder.
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Other Recordings: In addition to the core three, other physiological parameters are often monitored during sleep studies:
- Electrocardiogram (ECG or EKG): Records the electrical activity of the heart. This can help detect heart rate irregularities or other cardiac events that may occur during sleep.
- Respiratory Effort and Airflow: Sensors are used to monitor breathing patterns, including chest and abdominal movement (effort) and airflow through the nose and mouth. This is essential for diagnosing sleep apnea.
- Oxygen Saturation (Pulse Oximetry): Measures the level of oxygen in the blood. This helps identify periods of low oxygen levels, which can be a sign of sleep apnea or other respiratory problems.
- Limb Movements: Sensors attached to the legs can detect periodic limb movements, a common symptom of restless legs syndrome and periodic limb movement disorder.
In summary, studying sleep involves polysomnography, which employs EEG, EOG, EMG, and other recordings to characterize sleep stages, identify sleep disorders, and understand the physiological changes that occur during sleep.
