During which sleep stage are POSTS commonly observed?

The correct answer is that POSTS, or posterior slow waves, are commonly observed during Stage 1 sleep. In this stage, individuals are transitioning from wakefulness to sleep, and the brain begins to exhibit slower brain activity typical of early sleep. During Stage 1, theta waves become more prominent, and bursts of neuronal activity can be observed, including POSTS. These slow waves reflect a momentary slowing of neural activity as the brain moves into deeper stages of sleep.

In contrast, other sleep stages, such as Stage 2 and 3, show different brain wave patterns and characteristics. Stage 2 is marked by sleep spindles and K-complexes, while Stage 3 is primarily characterized by delta waves, indicating deeper sleep. REM sleep, on the other hand, is associated with rapid eye movement and a brain wave pattern that more closely resembles wakefulness. Therefore, the observation of POSTS aligns specifically with the initial stage of sleep, which is classified as Stage 1.