Which brain wave is predominant during deep sleep?

• A. Theta waves
• B. Alpha waves
• C. Hypnic jerk
• D. Delta waves

Answer: (D)

During deep sleep, the brain settles into slow, synchronized activity known as delta waves. These are low-frequency, high-amplitude patterns (about 0.5–4 Hz) that dominate slow-wave sleep, the deepest stage where the body’s restoration processes are most active. Other patterns relate to different states: theta waves show up in lighter sleep and drowsiness, alpha waves occur during relaxed wakefulness, and a hypnic jerk is a muscle twitch at sleep onset rather than a brain wave. So, delta waves best describe the brain activity of deep sleep.