Medical College Admission Test (MCAT) Psychological, Social, and Biological Foundations of Behavior (Psych/Soc) Practice Exam 2025 - Free MCAT Psych/Soc Practice Questions and Study Guide

In later sleep cycles, there is a characteristic pattern where REM sleep and non-REM sleep occur in a mixture. During a typical night's sleep, the cycle consists of multiple stages of non-REM sleep followed by periods of REM sleep.

In the earlier cycles, individuals typically spend more time in the deeper stages of non-REM sleep (such as stages 3 and 4) characterized by slow brain waves and less frequent awakenings. As the night progresses, the cycles shift, and the duration of REM sleep increases while deep non-REM sleep decreases. This leads to a pattern where both REM and non-REM sleep are present, with REM sleep becoming more prominent in the later cycles.

REM sleep is associated with increased brain activity, vivid dreaming, and physiological changes such as increased heart rate and breathing irregularities. The balance of these sleep stages is crucial for restorative sleep and cognitive functioning. Thus, it is accurate to say that later sleep cycles are characterized by a mixture of both REM and non-REM sleep.