Figure 1.

Systematic occurrences during wake and sleep. The figure demonstrates the minor physiological differences between wake and each of the sleep stages. Normal structural progression, displayed in the hypnogram at the top of the figure provides context surrounding the frequent shifts between states, and the subsequent reliance for accurately capturing physiological trends. Prominent physiological trends often characteristic of these individual states, which are each traditionally measured via separate methods, are comparable including brain activity, cardiac patterns (heart rate and blood pressure), respirations, eye movement, and muscle tone. REM physiology depicted is most representative of phasic REM. (BP, blood pressure; HR, heart rate; Hz, hertz; N1, non-rapid eye movement stage 1; N2, non-rapid eye movement stage 2; N3, non-rapid eye movement stage 3; REM, rapid eye movement).