Effect of total sleep deprivation on the landmarks of stage 2 sleep.

OBJECTIVE: To assess the effects of total sleep deprivation on sleep spindle and K-complex (KC) density.

METHODS: Eight healthy male subjects (mean age=23.4 years) participated in the experiment: they slept in the laboratory for 3 nights (one adaptation, one baseline, one recovery); baseline and recovery night were separated by a period of 40 h of continuous wake.

RESULTS: One night of total sleep deprivation caused a doubling of slow-wave sleep (SWS) amount, an increase of sleep efficiency and a reduction of the latencies of non-rapid eye movement (NREM) sleep stages during the recovery night. These effects were accompanied by a significant reduction in spindle density in the first sleep cycle of the recovery night. Mean KC density did not change as a result of total sleep deprivation, while KC density and inter-KC intervals showed linear trends across the first 4 sleep cycles, respectively decreasing and increasing. Finally, a clear evidence of an antagonist relationship between spindle and KC changes across sleep cycles was provided.

CONCLUSIONS: The present study further supports the existence of a reciprocal relationship between SWS and sleep spindles, but fails to show an increase of KC density after total sleep deprivation. The opposite time courses of spindle and KC density across sleep cycles points to an antagonist relation between the two main phasic events of NREM sleep. The latter result, together with the increase of inter-KC distance and the decrease of KC density across subsequent sleep cycles, is consistent with the hypothesis of a role of the spontaneous KC as the "forerunner" of delta waves.