What is the definition of a K complex?

What is the definition of a K complex?

• A. Negative wave followed by a positive wave, at least 0.5 second duration
• B. Negative wave followed by a positive wave, at least 1 second in duration
• C. 0.5Hz-2Hz with an amplitude of at least 75mV
• D. Positive wave followed by a negative wave, at least 0.5 second duration

Answer: (A)

A K-complex is defined by a large, slow negative deflection in the EEG that is immediately followed by a smaller positive deflection, with the whole biphasic complex lasting at least 0.5 seconds. This specific sequence and minimum duration are what set it apart from other transients, and it’s most commonly seen during stage N2 sleep, often in response to a sensory prompt or spontaneously as a brief arousal that the brain quickly suppresses to stay asleep. The other options don’t fit: the required sequence is negative first, then positive, not the reverse; the duration threshold is 0.5 seconds, not necessarily 1 second; and K-complexes aren’t defined by a particular frequency range or a fixed amplitude in millivolts—amplitude can vary and is not specified in those terms.

A K-complex is defined by a large, slow negative deflection in the EEG that is immediately followed by a smaller positive deflection, with the whole biphasic complex lasting at least 0.5 seconds. This specific sequence and minimum duration are what set it apart from other transients, and it’s most commonly seen during stage N2 sleep, often in response to a sensory prompt or spontaneously as a brief arousal that the brain quickly suppresses to stay asleep. The other options don’t fit: the required sequence is negative first, then positive, not the reverse; the duration threshold is 0.5 seconds, not necessarily 1 second; and K-complexes aren’t defined by a particular frequency range or a fixed amplitude in millivolts—amplitude can vary and is not specified in those terms.