Clinical Tools to Track Sleep


EEG is short for electroencephalogram, a test that detects and maps electrical activity in the brain. When neurons, specific cells found in the brain, activate, an electrical signal moves along the body of the cell. These electrical signals are what EEGs measure and record. An EEG helps track the different stages of sleep and is commonly used to diagnose brain disorders that involve seizure activity or sleep dysfunction. Other conditions that EEGs are used to diagnose include brain tumors, brain damage from a traumatic brain injury (TBI), brain dysfunction like encephalopathy, inflammation, strokes, and sleep disorders. EEGs are also used to confirm brain death in patients in persistent comas and find the right levels of anesthesia for someone in a medically induced coma.

To begin an EEG test, a medical professional will glue electrodes, small metal discs at the ends of recording thin wires, to a person’s scalp with conductive medical glue or tape. That’s why test subject should arrive with clean hair, with no hair product, to ensure secure placement of electrodes. The electrodes do not stimulate any activity, but simply record the electrical signals. The wires feed into an instrument that is able to amplify the brain waves for visualization on a monitor. Once the electrodes are fixed and the equipment is tested, the test subject will be instructed to do various activities to see how the brain responds. These may include falling asleep, opening and closing eyes, perform calculations, read, or look into a flashing light. A video recording will accompany the EEG recording. The combined recording will help the doctor diagnose and treat a condition.

Another kind of EEG, an ambulatory EEG (aEEG) can also be used for longer monitoring outside of a hospital setting. These are used much less for diagnostic purposes because without the video component, it is difficult to determine the difference between epileptic seizures and nonepileptic seizures.

When analyzing the results of the EEG, doctors look for patterns of brain activity that are higher or lower than what is typically observed. Faster waves and higher frequencies of brain waves can be indicative of a seizure. Unusually slow and lower frequencies of brain waves are associated with lesions in the brain that can be caused by tumors or a stroke. Some other conditions that alter wave activity might be brain trauma or drug intoxication.


Polysomnography is a specific kind of sleep study that combines an EEG with other body change monitors. This comprehensive test looks at brain waves, eye movements, heart rate, breathing pattern, blood oxygen level, body position, chest and abdominal movement, limb movement, and noises (such as snoring, talking, etc.). Below is a figure that shows all of the different testing equipment that can be used during a polysomnography test.

The results from a sample polysomnography test are displayed below. Clinicians will run and align the test to analyze what’s happening in different parts of the body at the same time.