Which statement about Non-REM sleep is true?

• A. Non-REM sleep is characterized by a lack of rapid eye movement.
• B. Non-REM sleep consists of four stages.
• C. Non-REM sleep occurs only during daylight hours.
• D. Non-REM sleep means there is no rapid eye movement and it consists of three stages of sleep which get progressively deeper.

Answer: (D)

Non-REM sleep is the portion of sleep where eye movements are minimal or absent and the night is divided into stages that reflect increasing depth of sleep. The best statement captures both key ideas: there is no rapid eye movement, and the sleep is organized into three stages (light, intermediate, and deep/slow-wave sleep) that become harder to wake someone from as you move through them. This progression through N1, N2, and N3 explains why sleep is restorative at different depths and why arousal becomes progressively more difficult.

Think of it in contrast to REM sleep, where rapid eye movements and more dream-like brain activity occur. Some choices either note only the absence of eye movements or wrongly describe the number of stages or when sleep happens (like during daylight). The fuller description—no REM and three progressively deeper stages—best fits how non-REM sleep is understood.