Written by the Fiveable Content Team • Last updated September 2025
Verified for the 2026 exam
Verified for the 2026 exam•Written by the Fiveable Content Team • Last updated September 2025
Definition
Non-Rapid Eye Movement (NREM) sleep is a type of sleep that is divided into three stages and characterized by slow brain waves. It's the period of sleep where we get our deepest, most restorative rest.
Related terms
Stage 1 Sleep: This is the lightest stage of NREM sleep, often defined by the presence of slow eye movements. This stage serves as a transition between wakefulness and deeper stages of sleep.
Stage 2 Sleep: The second stage of NREM where our heart rate slows and body temperature drops. Brain waves become slower with only occasional bursts of rapid waves called sleep spindles.
Slow-Wave Sleep (SWS): Also known as deep or delta sleep, this is the third stage in the cycle where brain activity slows down significantly. It's during this time that our bodies repair muscles and tissues, stimulate growth and development, boost immune function, and build energy for the next day.