Effects of rate of tone-pip stimulation on the evoked K-Complex.

The effects of rate of presentation on the evoked K-Complex were examined. In different conditions, brief duration tone pips were presented every 5, 10 or 30 s. Trials were sorted into those on which a K-Complex was or was not elicited and averaged separately. The evoked K-Complex consisted of two different negative components peaking at approximately 350 and 550 ms (respectively), followed by a positive component peaking at approximately 900 ms. K-Complexes were elicited more often in Stage 2 early and 2 late than in slow-wave sleep although the differences were not significant. K-Complexes were elicited more often in the Long ISI compared to the Short and Medium ISI conditions. When a K-Complex was evoked, the amplitude of N350 and N550 was greater for the Long ISI than for the Short or Medium ISI conditions. P900 amplitude remained invariant regardless of the ISI. A micro-analysis was carried out whenever 3 consecutive occurring K-Complexes were elicited. During the Short and Medium ISI conditions, N350 and N550 following the second and third occurrence of the K-Complex were significantly attenuated compared to the first occurrence. There was no difference in N350 and N550 amplitudes among the 3 consecutive occurrences during the Long ISI condition. The decay in amplitude over consecutive occurrences of the K-Complex might be a reflection of either habituation or refractory processes.