NREM Stage 1 (N1) sleep is characterized by all of the following EXCEPT?

NREM Stage 1 (N1) sleep is typically considered the transition phase between wakefulness and deeper stages of sleep. During this stage, several characteristic features are observed. One key aspect of N1 sleep is the emergence of vertex waves, which are sharp, wave-like patterns seen in the EEG. These are often present in the early part of NREM sleep as the body begins to relax and transition into a deeper sleep state.

Another characteristic of N1 sleep is the presence of slow rolling eye movements, indicating the very early stages of sleep. During this time, the brain transitions from an alpha rhythm, which is prevalent during relaxed wakefulness, to the mixed frequency patterns associated with sleep.

However, sleep spindles are not typical of N1 sleep; they primarily occur in NREM Stage 2 (N2). Sleep spindles are brief bursts of oscillatory brain activity that indicate the brain is moving to a deeper state of sleep and is not a feature associated with the initial stage of NREM sleep, making this choice the exception in the context of N1 sleep characteristics.