title: An examination of evoked K-complex amplitude and frequency of occurrence in the elderly.
abstract: The elderly consistently display lower levels of slow wave sleep (SWS), primarily because of the small amplitude of their delta activity. Given that delta electroencephalogram (EEG) and K-complexes are thought to be generated by the same mechanisms, it was hypothesized that K-complex amplitude and rate of production would be lower in the elderly. K-complex amplitude was assessed by averaging K-complex responses to auditory stimuli, and measuring the amplitude of the N550 component of the averaged evoked response. Ten young (five males and five females; mean age 23.10 +/- 5.36 years) and 10 elderly adults (six males and four females; mean age=75.60 +/- 4.48 years) who were neurologically healthy and free from medication spent two non-consecutive nights in the sleep laboratory. EEG was recorded from six gold plate electrodes (Fz, Fcz, Cz, Cpz, Pz and O2) referenced to A1 + A2. Tone clicks (1000 Hz), of varying intensity from 70 to 100 decibels above measured awake detection threshold, were presented binaurally during stage 2 sleep. Responses were classified according to whether they produced: a K-complex, a vertex sharp wave (VSW), both of these responses or neither response. They were then averaged separately for each response type. The elderly showed a substantially smaller N350 (averaged VSWs) and N550 amplitudes compared with the young subjects. The elderly also showed an augmented but delayed P2 component, followed by a long-lasting positive EEG shift. The smaller amplitude of the averaged K-complex N550 component is consistent with lower delta amplitudes previously reported in the elderly and with the hypothesis that K-complexes and delta activity share the same generator mechanisms. The enhanced P2 component and the long-lasting positive deflection in the EEG in the elderly indicate the existence of age differences other than smaller EEG amplitude.
authors.affiliation: Department of Psychology, University of Melbourne, Australia.
authors.forename: Kate
authors.initials: K
authors.lastname: Crowley
authors.forename: John
authors.initials: J
authors.lastname: Trinder
authors.forename: Ian M
authors.initials: IM
authors.lastname: Colrain
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000375:Aging / Q000502:physiology; D004569:Electroencephalography; D005071:Evoked Potentials / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D010507:Periodicity; D012189:Retrospective Studies; D012890:Sleep / Q000502:physiology; D012895:Sleep, REM / Q000502:physiology; D011795:Surveys and Questionnaires