FIGURE 13-12 Sleep Recording and Revelations (A) EEG patterns associated with waking with the four NREM sleep stages and with REM sleep. (B) Over a typical night’s sleep, a person undergoes several sleep state changes in roughly 90-minute periods. NREM sleep dominates the early sleep periods, and REM sleep dominates later sleep. The duration of each sleep stage is reflected in the thickness of each bar, which is color-coded to the corresponding stage in part A. The depth of each stage is graphed as the relative length of the bar.

Information from D. D. Kelley (1991). Sleep and Dreaming (p. 794). In E. R. Kandel, J. H. Schwartz, & T. M. Jessell (Eds.). Principles of Neuroscience. New York: Elsevier.