Glossary of Sleep-related terms

Stage 3 (NREM Stage 3, Delta Sleep, Slow Wave Sleep)

Stage 3, along with stage 4 sleep is often called Delta Sleep or Slow Wave sleep. The Stage 3 EEG record consists of 20% to 50% delta EEG waves. These delta waves have a slow frequency of 2 cps or slower, and amplitudes of more than 75 mV (high amplitude delta waves). Stage 3 sleep is deeper than stages 1 or 2; it takes a more intense stimulus to awaken someone in this sleep state. Stage 3 primarily appears in the first half of the sleep episode in adults.1