Polysomnography is a type of sleep study that involves the use of a polysomnographic machine, which measures brain activity and other data related to sleep. A polysomnographic technician monitors sleep patterns and records information after connecting the polysomnographic, or PSG, monitor to a sleeping subject. Physicians in a sleep clinic may use this data to test and diagnose a patient with a sleep disorder. Researchers may work with polysomnographic technicians to collect information for studies or perform tests for a product or medication.