MODEL RELEASED. Sleep research. Male patient (in the background) is wired up to somniography equipment used in a sleep research study. In the foreground a researcher at a monitor examines a data printout. Electrodes on the patient's head record electrical brain activity (a type of electroencephalograph or EEG); sensors on the face are used to measure tension or movement in various facial muscles during sleep. Heartbeat and breathing may also be monitored. A normal period of sleep consists of cycles in 5 phases. The first 4 phases are increasingly deeper sleep called Non- Rapid Eye Movement (NREM) sleep, followed by a fifth period of Rapid Eye Movement (REM) sleep.