What are some characteristics of stage N1 sleep?

Stage N1 sleep, also known as the transition between wakefulness and sleep, is characterized primarily by the presence of theta waves. Theta waves are brain waves that oscillate in the frequency range of approximately 4 to 7 Hz and are predominant during this light sleep stage. This stage marks the initial drop in consciousness where muscle activity begins to decrease, and it is relatively easy for an individual to be awakened.

The presence of theta waves distinguishes N1 sleep from the deeper stages of sleep where delta waves become more prominent. Delta waves, which are slower brain waves (0.5 to 4 Hz), are typically associated with deeper sleep stages (N3). Alpha waves, occurring during relaxed wakefulness and often present when eyes are closed, are not predominant in N1 sleep. Beta waves, indicative of alertness and active thinking, are also not characteristic of this early sleep stage, as they reflect a more awake state. Thus, recognizing theta waves as the defining characteristic helps to reinforce understanding of sleep stage classification.