Final answer:
Delta waves predominate during stage 4 NREM sleep, which is the deepest stage of sleep, characterized by the lowest frequency and highest amplitude brain waves and associated with restorative functions.
Step-by-step explanation:
Type of Wave Predominating During Stage 4 NREM Sleep
The type of wave that predominates during stage 4 NREM sleep is the delta wave. Delta waves are characterized by low frequency (less than 3 Hz) and high amplitude, making them the slowest and largest waves observed during sleep. During this stage, also known as deep sleep or slow-wave sleep, an individual's heart rate and respiration slow dramatically, and it is much more challenging to awaken someone.
Stage 4 NREM sleep is crucial for restorative functions and memory consolidation. Unlike alpha waves, which are present during the early part of stage 1 NREM sleep, or theta waves, which are characteristics of the end of stage 1 sleep and stage 2 sleep, delta waves signify the deepest stage of sleep prior to REM sleep.