Final answer:
During REM sleep, individuals experience high levels of physical activity and intense brain activity while their muscles are paralyzed. This state, known as paradoxical sleep, is associated with dreaming and may play a role in learning and memory processes.
Step-by-step explanation:
During REM sleep, individuals experience high levels of physical activity and intense brain activity, similar to when they are awake. However, the muscles are paralyzed, except for those necessary for circulation and respiration. This state is often referred to as paradoxical sleep. REM sleep is also associated with dreaming and is believed to play a role in learning and memory processes.