Abstract
Nocturnal transportation noise can disturb sleep by causing awakenings, sleep-stage changes or EEG arousals. However, not all external acoustic stimuli disrupt sleep. Processing of stimuli is modulated by transient EEG rhythms during sleep such as sleep spindles where sensory relay is hindered at a sub-cortical level. Thus, we investigated whether sleep spindle density rhythms predict arousability from acoustic stimulation (noise) during sleep. Twenty-six healthy participants (age: 19-33y, 12 female) were exposed to 80 railway noise events (RNE) that were played back in regular intervals during an 8-h night. For this, ten pre-recorded noise events were used, that differed with respect to maximum sound pressure level (SPL), event duration (SPL above 35 dB(A)), and slope of the SPL. Polysomnography and SPL of the noise events were recorded simultaneously during the night. Sleep and EEG arousals were scored according to standard criteria. Spindles on central channels were detected in EEG arousal and artefact free parts of sleep (NREM stages 1, 2 and 3) using an automatic scoring algorithm (http://spisop.org). Single RNE’s that occurred during stage 2 sleep were post-hoc classified as Non-arousal or Arousal trials depending on whether an EEG arousal occurred during the particular event duration. Depending on the noise event type, 12–48% of all RNE’s were associated with an EEG arousal that occurred particularly during the part of rising SPL (between the event onset and the maximum SPL). The mean spindle density during this period was a significant predictor in a logistic regression model (chi-square = 87.9, p < .001 with df = 2). The lower the mean spindle density, the higher was the arousal probability. We gained evidence that arousability from noise during sleep is modified by the spindle density during the part of rising SPL of a railway noise event. Whether acoustic stimuli themselves can trigger sleep spindle occurrence in humans remains to be investigated.
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