When are sleep spindles considered K complexes?

Sleep spindles are considered K complexes when they meet specific criteria, particularly during the process of sleep. This often includes the presence of sharp slow waves preceding the sleep spindles, and they can be elicited by auditory stimuli, such as sounds. This characteristic indicates an important aspect of the brain's activity during sleep, where the brain exhibits a response to external stimuli despite being in a sleep state. This interaction showcases how certain sleep waves function together, contributing to the understanding of sleep architecture and the brain's ability to integrate the external environment while in sleep.

In contrast, being a component of waking state, being followed by rapid eye movements, or occurring solely during deep sleep does not align with the specific definition regarding K complexes that involves their elicitation by sound and preceding sharp slow waves.