The N550 component of the evoked K-complex: A modality non-specific response?

A large amplitude late negative deflection peaking between 500 and 650 ms i s observable in the averaged K-complex wave-form. This peak is thus often l abelled the N550. 'N550' appears during stage 2 and is maintained into slow wave sleep but is not apparent during REM. Most studies have employed audi tory stimuli to elicit the K-complex. Two experiments were run to examine t he effects of stimulus modality on the topographical distribution of the N5 50. In the first experiment, the K-complexes were elicited in an auditory o ddball procedure. In the second experiment, K-complexes were elicited by re spiratory occlusions. Twenty-nine channel recordings were used to increase spatial resolution. N550 was substantially larger in the average of trials containing K-complexes than in trials in which a K-complex could not be ide ntified. N550 varied inversely in amplitude with the probability of accorda nce of the stimulus. The topographic distribution of the N550 was consisten t between experiments. It was bilaterally symmetrical and was maximal over fronto-central regions of the scalp. The results indicate that the N550 ref lects the activity of a modality non-specific, sleep dependent generator th at responds to both interoceptive and external stimulation.