US High School Psychology Practice Exam 2025 – Your All-in-One Guide to Exam Success!

The type of sleep characterized by rapid eye movement (REM) and high brain activity is known as REM sleep. During this stage, the brain exhibits activity patterns similar to those of wakefulness, which is why it is often associated with vivid dreaming. The body experiences atonia, a temporary paralysis of most voluntary muscles, which prevents the sleeper from acting out dreams. This stage typically occurs multiple times throughout the sleep cycle, with periods of REM sleep elongating with each cycle as the night progresses.

In contrast, the other stages mentioned differ significantly from REM sleep. Stage 2 sleep is associated with specific brain wave patterns and is characterized by a decrease in heart rate and body temperature; it does not involve the rapid eye movements characteristic of REM. Nocturnal sleep refers to sleep during nighttime hours and encompasses all sleep stages, not just REM. Deep sleep, or slow-wave sleep, features slow brain waves, reduced physiological activity, and is essential for physical restoration and growth, rather than the high brain activity seen in REM. Therefore, REM sleep is uniquely defined by its combination of active brain function and specific physical characteristics.