Which of the following is a common characteristic of REM sleep?

REM sleep, or Rapid Eye Movement sleep, is characterized by several distinct physiological and neurological features that contribute to its unique role in sleep cycles. One of the hallmark characteristics is increased brain activity. During REM sleep, brain waves become similar to those observed during wakefulness, which is essential for processes such as memory consolidation and learning, making it a crucial stage of the sleep cycle.

Additionally, during REM sleep, there is a physiological response involving the relaxation of voluntary muscles, a phenomenon often referred to as REM atonia. This is crucial for preventing the body from acting out dreams, which could potentially lead to injury.

The cardiac system also experiences unique changes during REM sleep; while heart rate may vary, it often shows periods of increased variability and can indeed increase in some individuals due to heightened emotional responses during dreaming.

Because all these characteristics are present in REM sleep, the correct response reflects the importance of recognizing that REM sleep includes elements of increased brain activity and muscle atonia, along with variable heart rate, distinguishing it from other sleep stages.