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

Rapid eye movements, commonly referred to as REM, are a hallmark characteristic of this particular sleep stage. During REM sleep, the eyes move quickly in various directions, even though the eyelids remain closed. This unique activity is associated with vivid dreaming, which often occurs during this phase.

Furthermore, REM sleep is characterized by other physiological changes, such as increased brain activity and irregular heart rates, contrasting with the option of decreased heart rate. Muscle tone, notably, is actually reduced during this sleep stage, which is important for preventing individuals from acting out their dreams. Dreamless sleep is not characteristic of REM, as this stage typically involves intense dreaming.

Overall, the presence of rapid eye movements is a definitive criteria that differentiates REM sleep from other sleep stages.