The brain is most active during which portion of each sleep cycle? a. the beginning of each sleep cycle b. the middle of each sleep cycle c. the end of each sleep cycle d. the brain is not active during the sleep cycle.

I think the correct answer from the choices listed above is option B. It is during the middle of each sleep cycle that the  brain is most active. At this point. our breathing becomes more rapid, irregular, and shallow, our eyes move rapidly in various directions, and our limb muscles become temporarily paralyzed. Our heart rate increases and our blood pressure rises. Hope this helps.