What sleep stage requires 20% to 50% of the epoch to consist of waves of 2 cps or slower with amplitudes greater than 75 uV?

The correct answer is Stage 3. This sleep stage is characterized by slow-wave sleep, which is essential for restorative processes in the body. In Stage 3, the EEG shows delta waves, which are defined as waves with a frequency of 2 cycles per second (cps) or slower, and they must predominantly have amplitudes greater than 75 microvolts (uV). The requirement for 20% to 50% of the epoch to consist of these delta waves is crucial for classifying it as Stage 3 sleep.

This stage of sleep is pivotal as it plays a significant role in physical recovery, growth, and immune function. The presence of these slow waves indicates a deep level of sleep, which distinguishes it from lighter stages of sleep. The specific criteria regarding wave frequency and amplitude help sleep technologists and clinicians evaluate sleep architecture and diagnose sleep disorders accurately.

Other stages, such as Stage 1 and Stage 2, have different characteristics regarding EEG patterns, and REM sleep is primarily associated with rapid eye movements and a different type of brain wave activity that does not fit the criteria given in the question.