What distinctive feature is observed on an EEG for stage 2 sleep?

Stage 2 sleep is characterized by the presence of sleep spindles, which are bursts of oscillatory brain activity that are typically between 12 to 16 Hz and can last for about 0.5 to 2 seconds. These spindles are significant because they are believed to play a role in memory consolidation and learning processes. In addition to sleep spindles, stage 2 sleep may also include K-complexes, which are sudden bursts of brain activity that are thought to help the body remain asleep and reduce perception of external stimuli.

Theta waves are primarily associated with lighter stages of sleep (Stage 1) and relaxation, while delta waves are more prevalent in deeper sleep stages (Stage 3 and 4). Beta waves are associated with active, alert states of consciousness. Therefore, while delta and theta waves are important in different sleep stages, it is the presence of sleep spindles that distinctly marks stage 2 sleep.