REM sleep is associated with which of the following physiological activities?

REM (Rapid Eye Movement) sleep is characterized by a unique array of physiological activities. During this stage of sleep, the brain is highly active, resembling wakefulness, which is typically indicated by variable and irregular heart rates and respiration patterns. This is due to the activation of the autonomic nervous system, which can lead to fluctuations in cardiovascular and respiratory response.

The irregularities in heart rate and breathing during REM sleep are also associated with the occurrence of vivid dreams, as the brain processes information and experiences during this phase. This dynamic nature of heart and respiratory rates is in contrast to other sleep stages, where vital signs tend to be more stable and consistent.

Other choices provide incorrect representations of REM sleep: consistent heart rate and respiration would denote a sleep stage where the body is more relaxed and stable, decreased brain activity does not align with the high brain activity found in REM, and stable muscle tone is inaccurate since REM sleep is characterized by atonia, or muscle paralysis, preventing individuals from acting out their dreams. Therefore, variable heart rate and irregular respiration are quintessential features of REM sleep.