1 AU - Aeschbach D AU - Borbely AA IN - Institute of Pharmacology, University of Zurich, Switzerland. TI - All-night dynamics of the human sleep EEG. SO - J Sleep Res 1993;2:70-81 AB - The dynamics of the sleep EEG was investigated by all-night spectral analysis of 51 sleep records. Power density was calculated for 1-Hz bins in the 0.25-25.0 Hz range. Values in non-rapid-eye-movement sleep (NREMS) were higher than in REMS in the 0.25-16.0 Hz range, and lower in the 18.25-22.0 Hz range. Power density in the 0.25-12.0 Hz range showed a declining trend over the first four NREMS episodes, which, depending on the frequency bin, could be approximated by non-linear or linear decay functions. In the frequency range of sleep spindles (12.25-15.0 Hz), power density in the 13.25-15.0 Hz band showed an increasing trend between NREMS episode 2 and NREMS episode 4. A correlation matrix of 25 1-Hz bins revealed for NREMS a negative correlation between slow-wave activity (SWA; 0.25-4.0 Hz) and activity in the spindle frequency range. This negative correlation was highest in the first NREMS episode and diminished progressively over the subsequent NREMS episodes. Within NREMS episodes, the values in the spindle frequency range showed a U-shaped time course, the trough coinciding with a high level of SWA. By contrast, in both the early and late part of the episode the two types of activity changed in the same direction. The results are consistent with recent electrophysiological studies indicating that the establishment of NREMS is associated with a progressive hyperpolarization of thalamocortical neurons during which the membrane potential exhibits oscillations first in the spindle frequency range and then in the range of SWA. IS - 0962-1105 2 AU - Geering BA AU - Achermann P AU - Eggimann F AU - Borbely AA IN - Institute of Pharmacology, University of Zurich, Switzerland. TI - Period-amplitude analysis and power spectral analysis: a comparison based on all-night sleep EEG recordings. SO - J Sleep Res 1993;2:121-129 AB - Both period-amplitude analysis (PAA) and power spectral analysis (PSA) were performed on all-night human sleep EEG recordings obtained from 11 subjects. The comparison of the two methods was based on the PAA variables time in band (a wave incidence measure) and rectified amplitude, and on the PSA variables spectral power density and spectral amplitude (the square root of power). The mean time course of these variables was determined for the first 4 nonREM-REM sleep cycles. Spectral power density and spectral amplitude in the delta range were high in nonREM sleep and low in REM sleep, and showed a declining trend over consecutive nonREM sleep episodes. In the frequency range below 2 Hz, rectified amplitude was highly correlated with both time in band and spectral amplitude, and there was no evidence for a dissociation between wave amplitude and wave incidence measures. However, in frequencies above 2 Hz, the modulation of time in band was a mirror image of that below 2 Hz. This result does not reflect a property of the data, but is inherent to the methodology applied. The reversal point of modulation was merely shifted when the high-pass filter settings were changed. It is concluded that band-pass filtering is necessary prior to PAA even for the analysis of the lowest frequency range, and that the indiscriminate use of PAA may give rise to spurious results. IS - 0962-1105 3 AU - Kattler H AU - Dijk DJ AU - Borbely AA IN - Institute of Pharmacology, University of Zurich, Switzerland. TI - Effect of unilateral somatosensory stimulation prior to sleep on the sleep EEG in humans. SO - J Sleep Res 1994;3:159-164 AB - The hypothesis that local activation of brain regions during wakefulness affects the EEG recorded from these regions during sleep was tested by applying vibratory stimuli to one hand prior to sleep. Eight subjects slept in the laboratory for five consecutive nights. During a 6-h period prior to night 3, either the left or the right hand was vibrated intermittently (20 min on - 8 min off), while prior to night 5 the same treatment was applied to the contralateral hand. The sleep EEG was recorded from frontal, central, parietal and occipital derivations and subjected to spectral analysis. The interhemispheric asymmetry index (IAI) was calculated for spectral power in nonREM sleep in the frequency range of 0.25-25.0 Hz for 0.5-Hz or 1-Hz bins. In the first hour of sleep following right-hand stimulation, the IAI of the central derivation was increased relative to baseline, which corresponds to a shift of power towards the left hemisphere. This effect was most prominent in the delta range, was limited to the first hour of sleep and was restricted to the central derivation situated over the somatosensory cortex. No significant changes were observed following left-hand stimulation. Although the effect was small, it is consistent with the hypothesis that the activation of specific neuronal populations during wakefulness may have repercussions on their electrical activity pattern during subsequent sleep. IS - 0962-1105 4 AU - Achermann P AU - Beersma DGM IN - Institute of Pharmacology, University of Zurich, Switzerland. TI - Changes of sleep EEG slow-wave activity in response to sleep manipulations: To what extent are they related to changes in REM sleep latency ? SO - J Sleep Res 1995;4:23-29 AB - Sleep interventions may have direct effects on slow-wave activity (SWA, i.e. power of the sleep EEG signal in the 0.75 - 4.5 Hz range) as well as indirect ones caused by changes in REM sleep (REMS) latency. The effects of changes in REMS latency on SWA were investigated by analyzing simulations with a mathematical model. Mean SWA in the first non-REMS episode shows an initial increase and a later decline as a function of REMS latency. In the second non-REMS episode, mean SWA decreases with increasing REMS latency. These results of the simulations were validated with experimental data. In the evaluation of the effects of sleep interventions on SWA the effects of the timing of REMS have to be accounted for. The analysis of SWA over a sufficiently long constant amount of time spent in non-REMS proves to be relatively independent of REMS latency, which allows conclusions about the effects of sleep interventions on SWA per se. IS - 0962-1105