The spontaneous K-complex during stage 2 sleep: is it the 'forerunner' of delta waves?

The hypothesis that K-complexes (KCs) contribute to the process of synchron ization leading to Slow-Wave Sleep (SWS) was evaluated by measuring their d ynamic evolution across sleep cycles and before transitions to rapid eye mo vement (REM) or to SWS. KC density and inter-KC intervals respectively decr eased and increased across the sleep cycles, revealing linear trends. Compa risons among transitions from stage 2 to SWS or to REM sleep showed a preva lence of KCs before the shift to SWS as compared to REM. Changes in KC dens ity before the shift to SWS were fitted by a linear regression, at variance with the transition to REM sleep. Intra-night variations of KCs, paralleli ng the well-known decrease of slow waves across sleep cycles, and intracycl e variations before shifting to SWS, both converge to indicate that KCs can be considered as the forerunner of delta waves. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.