Final answer:
Sleep stages 3 and 4 are characterized by delta waves in the EEG, representing deep, restorative sleep with low frequency and high amplitude wave patterns.
Step-by-step explanation:
Sleep stages 3 and 4 are characterized by the presence of a delta waves EEG record. These stages are often referred to as deep sleep or slow-wave sleep due to the low frequency (less than 3 Hz), high amplitude brain wave patterns. It is during this stage that an individual's heart rate and respiration slow dramatically, and it becomes much more difficult to awaken the individual. Delta waves are the hallmark of stages 3 and 4, representing the deepest levels of sleep, which are essential for restorative processes.