Figure 2.

Hypnograms illustrating and comparing sleep architecture between a younger and an older adult. The younger adult hypnogram (A) displays a regular cyclicity, with appropriate total sleep time (8 h), five sleep cycles, few arousals, more N3 sleep (slow-wave sleep) concentrated in the first half of the night and more REM sleep concentrated in the second half of the night. Conversely, the older adult hypnogram (B) displays a more fragmented sleep pattern, with less clearly identifiable sleep cycles, less N3 sleep, reduced total sleep time, and early awakening.