What characterizes Stage 2 sleep as observed through EEG?

Stage 2 sleep is characterized by specific brain wave patterns observed through electroencephalography (EEG). Bursts of brain wave activity, known as sleep spindles, are a hallmark of this sleep stage. These sleep spindles represent short bursts of oscillatory brain activity that are thought to play a role in memory consolidation and are prominent during Stage 2 sleep.

Additionally, Stage 2 sleep features characteristics such as K-complexes, which are high-amplitude waves that can occur in response to external stimuli. This combination of sleep spindles and K-complexes helps differentiate Stage 2 from other stages of sleep, particularly the deeper Stage 3 and rapid eye movement (REM) sleep.

While delta waves are typically associated with deeper sleep stages (specifically Stage 3), and alpha waves are generally more prevalent during relaxed wakefulness rather than during sleep, it is the bursts of brain wave activity, or sleep spindles, that define Stage 2. Thus, the presence of these bursts is the reason why the correct characterization of Stage 2 sleep is recognized through EEG.