Answer: 1. The human body cycles through two phases of sleep, (1) rapid eye movement (REM) and (2) non-rapid eye movement (NREM) sleep, which is further divided into three stages, N1-N3. Each phase and stage of sleep includes variations in muscle tone, brain wave patterns, and eye movements.
2. The activation-synthesis theory is a neurobiological explanation of why we dream. The question of why people dream has perplexed philosophers and scientists for thousands of years, but it is only fairly recently in history that researchers have been able to take a closer look at exactly what happens in the body and brain during dreaming.