What happens during a sleep study? First of all, the American Academy of Sleep divides sleep into two broad categories: non REM and REM. REM stands for Rapid Eye Movement sleep. Within the non-REM category there are subcategories and we divide them into three other stages plus wake. To figure out the different stages of sleep, and also what you're doing during sleep through the whole approximately eight hours, we have multiple electrodes and various other things that we look at very closely. One of the things we look at is the brain waves, or EEG. We know when certain phases of sleep occur and what kind of patterns there should be. The other thing we look at is the eye movements or EOG and that will help us decide basically between REM and non-REM. The other one we look at is limb movements and chin movements which is very important, again, to decipher and decide when REM and non-REM occur. The other thing we look at very closely is respiratory channels to find out how you're breathing. We look at the chest movement and the abdomen movement and we also monitor your oxygenation very closely, second by second. And we also look at your heart to see what goes on. This gives us ideas of what is going on as far as apneas and non-apneas, obstruction, and various other stages of sleep that we need to go and help you sleep better.