Examining the Effects of Slow-Wave Activity Disruption on Waking EEG Theta Activity

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Introduction: The two-process model of sleep postulates that sleep propensity increases throughout the day, and decreases with sleep as a homeostatic process. Both EEG delta activity (slow-wave) during sleep, and EEG theta activity during waking have been shown to increase with extended waking, and decrease following sleep, suggesting that both of these measures are markers of sleep propensity. In individuals with major depressive disorder, however, altered patterns of slow-wave activity have been noted, suggesting that sleep homeostasis is dysregulated. This study aimed to examine EEG theta activity in a sample of healthy and depressed individuals following one night of baseline, and one night of selective slow-wave disrupted sleep. Methods: 25 participants (13 diagnosed with Major Depressive Disorder (MDD) and 12 healthy controls (HC)) were recruited. Following one night of adaptation sleep, participants underwent one night of baseline sleep, and one night of selective slow-wave disruption by auditory stimuli. In the evening, before sleep, and in the morning following sleep, waking EEG was recorded from participants in an upright position, with eyes open. Results: A repeated measures ANOVA revealed a significant threeway interaction, F(1,23)=5.33, p<.05, between group (HC,MDD), time of day (AM,PM), and condition (baseline, disruption), such that AM theta activity was significantly lower following slow-wave disruption in those with MDD. There were no significant changes in theta activity in healthy controls. Conclusion: The present results revealed that following slow-wave disruption, waking EEG theta activity decreased in those with MDD, but not in healthy controls. This may suggest that SWA plays a different role in the homeostatic regulation of sleep in HC, and in MDD.




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