Which activity is commonly increased during normal drowsiness (NREM Stage N1)?

During normal drowsiness, specifically in NREM Stage N1, theta activity is the predominant wave form observed on the electroencephalogram (EEG). This stage marks the transition from wakefulness to light sleep, and it is characterized by the presence of both theta waves and some alpha waves. However, the defining feature of this stage is the increased theta activity, which typically ranges from 4 to 8 Hz.

Theta waves are often associated with light sleep and the early stages of sleep onset. As a person drifts from wakefulness into deeper stages of sleep, the prevalence of theta waves increases, reflecting the changes in brain activity as the body prepares for more restful sleep. This differs from other types of brain wave activity seen in different sleep stages or states of alertness.

In contrast, delta activity, which is indicative of deep sleep (NREM Stages N3 and N4), is not prominent during N1. Beta activity is typically observed during active, alert states when the individual is awake and engaged with their environment. Alpha activity, while present, starts to diminish as one transitions from wakefulness into N1, rather than increasing. Thus, theta activity is the hallmark of NREM Stage N1 during the drowsy phase