Final answer:
Stage 4 of the sleep cycle is the deepest NREM sleep stage, characterized by delta waves, unlike Stage 2 which features sleep spindles and K-complexes. REM sleep involves rapid eye movements and dreams.
Step-by-step explanation:
A student has asked which statement is true about Stage 4 of the sleep cycle. Stage 4 is the deepest stage of NREM sleep, and it is characterized by low frequency, high amplitude delta waves which make it harder to awaken someone. This stage is known for being restorative, and during it, an individual's heart rate and respiration slow down significantly.
Sleep spindles and K-complexes are most often associated with Stage 2 of NREM sleep. These features help to identify this particular stage on an EEG and are thought to play a role in learning and memory. REM sleep, on the other hand, involves rapid eye movements and brain waves similar to those observed during wakefulness; it is a period of sleep where dreaming occurs and muscle atonia is present.