Which of the following is a characteristic of K complexes in EEG recordings?

K complexes are a specific waveform seen in EEG recordings, particularly during sleep. They are typically associated with the transition between sleep stages and are most commonly observed during stage 2 (NREM) sleep. One defining characteristic of K complexes is their presence during non-REM sleep, and they can serve as a response to external stimuli.

The correct answer highlights that K complexes are absent during drowsiness, which typically represents a lighter stage of sleep or a transition into sleep. This absence is significant because K complexes are more established in deeper sleep stages. Drowsiness tends to manifest different brainwave patterns, such as theta waves, rather than K complexes.

Understanding the context of EEG patterns during various stages of sleep allows for a clearer distinction in identifying the presence or absence of certain waveforms, such as K complexes, in relation to the depth of sleep.