About a century ago, Nathaniel Kleitman, Eugene Aserinsky, and the other pioneering sleep researchers of the early 1900s characterized the K-complex; a figment of sleep architecture found during the early stages of NREM sleep that is highly distinguishable from the dominating high frequency, low density EEG signals because of its mountainous shape. Though K-complexes appear spontaneously across the early stages of NREM (more precisely stage 2) much like the sleep spindles, they can be voluntarily induced by transient noises like a knock at the door.
In May of 2009, neurophysiological assessments conducted by a massive group of researchers (certainly not atypical for a Science or Nature publication) unveiled that the human K-complex represents cortical “off-lining”. What does this mean??
As a prelude, the frequency and amplitude of EEG signaling characteristic of each NREM and REM stage of sleep are largely dependent on the number of neuron recruitment or cross-talk. High amplitude, low frequency EEG waves generated during slow wave sleep result from substantial and synchronous cross talk and firing amongst neurons in thalamocortical (thalamus + cortex) brain areas or to quote a neuro prof “neurons that wire together, fire together.” In constrast, the low amplitude, high frequency EEG signaling common of REM and light NREM sleep result from weak synchronous cross talk and firing among neurons.
To return to Cash’s work, an isolated cortical down-state hypothesized to be characteristic of K-complexes would mean that a K-complex results from LESS activation or LESS recruitment of neurons which paradoxically, somehow, in some way, generate this: HIGH AMPLITUDE, “SYNCHRONOUS” activity.
But 1.5 yrs later (this week’s edition of Science), someone has contested this finding and presented neurophysiological evidence illustrating that a K-complex is comprised of a sequential negative (reduced activation)-positive (potentiated activation)-negative (reduced activation) cortical state.
Who’s correct??? I don’t know! But hopefully this letter will spur more letters to the Editors. In support of this proposed counterintuitive relationship between cortical “off-lining” and the formation of K-complex, high amplitude, low frequency EEG waves are similarly found during an epileptic seizures, which of course, is due to inadequate cross talk or miscommunication between neurons.
At the same time, this type of disagreement, which should be embraced by all scientists, is certainly what advances any field. Considering all viewpoints is how the greatest, most cherished leaders in history (FDR, Lincoln) became successful (and correct), so why shouldn’t scientists?? Particularly for the betterment of the public.
Cash, S., Halgren, E., Dehghani, N., Rossetti, A., Thesen, T., Wang, C., Devinsky, O., Kuzniecky, R., Doyle, W., Madsen, J., Bromfield, E., Eross, L., Halasz, P., Karmos, G., Csercsa, R., Wittner, L., & Ulbert, I. (2009). The Human K-Complex Represents an Isolated Cortical Down-State Science, 324 (5930), 1084-1087 DOI: 10.1126/science.1169626