[Neurobiological disturbances in insomnia: clinical utility of objective sleep measures]

Numerious studies conducted over the last 40 years assessing different physiological domains including autonomic nervous system status, whole body and brain metabolic rate, stress and immune system activity suggest that (1) insomnia is a disorder of physiologic hyperarousal present throughout 24-hour sleep-wake cycle, and (2) insomnia and sleep loss are two distinct states. Central nervous system hyperarousal, either as pre-existing and/or induced by psychiatric pathology and worsened by stressful events, as well as aging- and menopause-related physiological decline of sleep mechanisms appears to be at the core of this common sleep disorder. Finally, there is emerging evidence that the levels of physiologic hyperarousal are directly related to the degree of polysomnographically documented sleep disturbance in insomnia patients, suggesting that objective measures of sleep duration in insomnia may be a useful marker of the medical severity of the disorder.