title: Human high frequency somatosensory evoked potential components are refractory to circadian modulations of tonic alertness.
abstract: The impact of vigilance states, such as sleep or arousal changes, on the high-frequency (600 Hz) components (HFOs) of somatosensory evoked potentials (SEPs) is known. The present study sought to characterize the effects of circadian fluctuations of tonic alertness on HFOs in awake humans. Median nerve SEPs were recorded at four times during a 24-hour waking period. In parallel to the SEP recordings, a reaction-time (RT) task was performed to assess tonic alertness. Additionally, the spontaneous EEG was monitored. The low-frequency SEP component N20 and the early and late HFO parts did not change across the measurement sessions. In contrast, RTs were clearly prolonged at night and on the second morning. EEG also showed increased delta power at night. HFOs are sensitive to pronounced vigilance changes, such as sleep, but are refractory to fluctuations of tonic alertness. Tonic alertness is regarded to be the top-down cognitive control mechanism of wakefulness, whereas sleep is mediated by overwhelming bottom-up regulation, which seems apparently more relevant for, at least in part, subcortically triggered high-frequency burst generation in the ascending somatosensory system.
authors.affiliation: Department of Neurology, University Hospital Aachen, Germany. rgobbele@ukaachen.de
authors.forename: René
authors.initials: R
authors.lastname: Gobbelé
authors.forename: Till D
authors.initials: TD
authors.lastname: Waberski
authors.forename: Dinah
authors.initials: D
authors.lastname: Thyerlei
authors.forename: Melanie
authors.initials: M
authors.lastname: Thissen
authors.forename: Bruno
authors.initials: B
authors.lastname: Fimm
authors.forename: Fabian
authors.initials: F
authors.lastname: Klostermann
authors.forename: Gabriel
authors.initials: G
authors.lastname: Curio
authors.forename: Helmut
authors.initials: H
authors.lastname: Buchner
mesh_terms: D000328:Adult; D001143:Arousal / Q000502:physiology*; D001683:Biological Clocks / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D011930:Reaction Time / Q000502:physiology*; D012033:Refractory Period, Psychological / Q000502:physiology*