Final answer:
NREM stage 4 sleep is characterized by slow delta waves, with low frequency and high amplitude, indicating deep rest. Heart rate and respiration slow dramatically, contrasting the rapid eye movements and higher brain activity associated with REM sleep.
Step-by-step explanation:
The characteristics of NREM stage 4 sleep, often considered the same as NREM stage 3 or as deep sleep, primarily involve slow delta waves. These delta waves are of low frequency (less than 3 Hz) and high amplitude, indicating a state of deep rest. During NREM stage 4, an individual's heart rate and respiration slow dramatically, which contrasts with states like REM sleep or wakefulness that are characterized by higher rates of physiological activity and brain waves similar to those observed when a person is awake.
Therefore, the correct answer to the question regarding the characteristics of NREM stage 4 is a) Slow delta waves. The other options, including rapid eye movements (b), heightened brain activity (c), and increased heart rate (d), are not characteristics of NREM stage 4, but rather of REM sleep and other phases of wakefulness.
Sleep spindles and K-complexes, which are associated with stage 2 of NREM sleep, also do not describe NREM stage 4. It's important to recognize that sleep stages are identified based on specific patterns of brain activity, body physiology, and other distinctive features captured primarily through the use of EEG measurements.