During which sleep stage is the arousal threshold the highest?

The arousal threshold is highest during N3 sleep, which is known as deep sleep or slow-wave sleep. In this stage, the brain exhibits delta wave activity, which is associated with the most restorative aspects of sleep. Because N3 is a profound stage of sleep, it requires a stronger stimulus to provoke an arousal compared to the lighter stages of sleep, such as N2 or REM. This high arousal threshold during N3 allows for more restorative processes to occur without frequent disturbances from external stimuli.

In N2, while the arousal threshold is elevated above the awake state, it is not as high as in N3, making it easier to awaken individuals. During REM sleep, although vivid dreaming occurs and the body is typically more active, the arousal threshold is lower than in N3. During the awake state, arousal is immediate and requires little to no stimulus. The contrast in arousal thresholds illustrates the varying depth of sleep stages, and highlights the unique characteristics of N3 as the stage with the greatest resistance to awakening.