Final answer:
An electroencephalogram from an adult in stage 4 sleep would show an abundance of delta waves, indicating deep NREM sleep.
Step-by-step explanation:
An electroencephalogram (EEG) obtained from an adult in stage 4 sleep would likely display an abundance of delta waves. Sleep is organized into several stages characterized by distinct patterns of brain waves, with stage 4 sleep, also known as NREM stage 3 or deep sleep, being marked by low frequency (less than 3 Hz), high amplitude delta waves. Delta waves represent the deepest level of NREM sleep, where heart rate and respiration slow dramatically, and it is much more difficult to awaken someone.