Brain activity during sleep

A) is relatively uniform, and does not change throughout the night.
B) is very similar to activity during the waking state.
C) is almost nonexistent.
D) is correlated with changes in muscle tension, breathing, and other physiological responses.

Answer: D
Rationale: Sleep is characterized by rhythms of brain activity. These changes in brain activity correspond to physiological changes, such as decreases in breathing, heart rate, and blood pressure as the sleeper passes through sleep stages 1-4. While it is true that EEG activity during REM sleep is very similar to activity during the waking state, this is not the case for brain activity during the non-REM stages.