The introduction reads as follows: Looking in on a sleep study, you’ll see that the brain is actually very active during sleep, cycling through non-REM stages and ending in REM sleep approximately five times during the night. Transitions between stages are clearly visible as shifts in EEG patterns. Graphs illustrating the human sleep cycle typically present an 8-hour time span, as shown below. But this doesn’t tell the whole story of sleep. The amount of time spent sleeping and the content of our sleep changes across the life span. Currently, only two thirds of U.S. adults get the recommended minimum of 7 hours per night (Liu et al., 2016).
At the upper right is an image of a young woman wearing a blue cap covered by multiple electrodes, with more electrodes taped to her forehead and around her eye. Another image shows a screen displaying multiple rows of brain waves. The caption reads, “This sleep study participant wears electrodes that will measure her brain waves and body movements during sleep.” At the right is an image of a brain wave. The start of the wave shows many similar, high-amplitude, high-frequency waves, followed by a flatter, irregular wave. An arrow labeled “Sleep” indicates the point where the waves change. The caption reads, “Looking at brain waves allows us to trace a person’s stage of sleep. Here we can see a clear shift from waking to sleeping patterns. (FROM DEMENT & VAUGHAN, 1999.)” A graph labeled “Human Sleep Stages” shows sleep patterns by time over 8 hours and the corresponding appearance of EEG patterns. The caption reads, “A typical night's sleep has 4 or 5 multistage sleep cycles, each lasting approximately 90 minutes. Each cycle includes at least 1 non-REM and 1 REM stage. Pattern and duration of stages differ over the course of the night. “
There are five sleep stages on the graph. The cycle times and wave appearances for each follow:
The lower graph shows the amount of non-REM sleep, REM sleep, and waking hours experienced according to age. The caption reads, “As we age, we need fewer hours of sleep, and the proportion of time spent in REM diminishes.” The X-axis is labeled “Age in years” and shows values from 0 to 10 in increments of 2, and then 20 to 90 in increments of 10. The Y-axis is labeled “Hours” and shows values from 0 to 24 in increments of 4. For the non-REM sleep, the graph starts at 8 hours for age 0 slowly decreasing to 7 hours at age 20, and then slowly decreasing to slightly less than 4 hours at age 90. For the REM Sleep, the graph starts at slightly over 16 (or 8 hours of REM), gradually decreasing to 8 (or 1 hour of REM) at age 20, then maintaining approximately 1 hour of REM sleep across the graph. A callout to the age 0 mark reads, “REM is 50% of total sleep time at birth.” A callout to the age 85 mark reads, “REM decreases to 20% of total sleep by age 85.”