Objective: Pathophysiological models of insomnia invoke the concept of 24-hour hyperarousal, which could lead to symptoms and physiological fi ndings during waking and sleep. We hypothesized that this arousal could be seen in the waking electroencephalogram (EEG) of individuals with primary insomnia (PI), and that waking EEG power would correlate with non-REM (NREM) EEG. Methods: Subjects included 50 PI and 32 good sleeper controls (GSC). Five minutes of eyes closed waking EEG were collected at subjects' usual bedtimes, followed by polysomnography (PSG) at habitual sleep times. An automated algorithm and visual editing were used to remove artifacts from waking and sleep EEGs, followed by power spectral analysis to estimate power from 0.5-32 Hz. Results: We did not fi nd signifi cant differences in waking or NREM EEG spectral power of PI and GSC. Signifi cant correlations between waking and NREM sleep power were observed across all frequency bands in the PI group and in most frequency bands in the GSC group. Conclusions: The absence of signifi cant differences between groups in waking or NREM EEG power suggests that our sample was not characterized by a high degree of cortical arousal. The consistent correlations between waking and NREM EEG power suggest that, in samples with elevated NREM EEG beta activity, waking EEG power may show a similar pattern.
S C I E N T I F I C I N V E S T I G A T I O N SU p to one-third of adults in the US complain of problems with sleep, and approximately 10% to 15% meet criteria for insomnia disorder.1,2 Primary insomnia, a disorder characterized by diffi culty falling asleep, staying asleep, or early awakening without signifi cant comorbid psychiatric or physical illness, has long been used as a model to study the pathophysiology of insomnia.3 Multiple studies have demonstrated that insomnia is associated with physiological markers of elevated arousal during both wakefulness and sleep, suggesting that 24-hour hyperarousal may be a defi ning feature of this condition.4,5 The 24-hour hyperarousal model has been supported by data including increased whole-body metabolic rate during waking and sleep, increased ACTH and cortisol secretion before and during early sleep, and elevated heart rate and beta frequency spectral power during non-REM (NREM) sleep.
5-9Impaired cognitive performance may also be related to hyperarousal and sleep disruption in insomnia.10 Physiological measures of hyperarousal or stress, such as HPA axis activation with increased cortisol secretion, may constitute one mechanism by which insomnia is a risk factor for development of depression associated with increased stress.
11-13Multiple studies have looked at quantitative electroencephalogram (EEG) as a marker of arousal during sleep in individuals with insomnia. One of the earliest studies identifi ed a slower increase and reduced levels of power in all frequency bands below beta frequency during NREM, coupled with increased 14 This fi nding of elevated beta frequency spectral power in sleep has been documented i...