Neurobiological Mechanisms In Chronic Insomnia

Abstract

This article grapples with the notion that insomnia can or should be defined in physiologic terms. It is proposed that insomnia is better understood from a neurobiological perspective. A review of the neurobiology of sleep and wakefulness is provided with a special emphasis on the implications for insomnia. Following the review it is suggested that a complete understanding of insomnia will require that the neurobiologic characterization of insomnia be informed by modern cognitive concepts and methods.

Keywords: ARAS; Homeostasis; Insomnia; Neurobiology; VLPO; inhibition of wakefulness.

Figure 1

This figure represents ascending pathways that lead to cortical desynchronization (activation). While the cholinergic and monoaminergic branches of this system have been well characterized, orexinergic component (and its contribution to the consolidation of wakefulness) is relatively new. One of the many important aspects of this system is that this arousal system is not the same as the ARAS (the Ascending Reticular Activation System [the fight or flight system]) anatomically of functionally. With respect to the latter, the orexin system appears to be under the control of, or intimately related to, the circadian system.

Figure 2

This figure provides a simplified representation of the “Sleep Switch”, i.e., the circuit and ascending pathways that lead to cortical synchronization (deactivation). One of the many important aspects of this system is the mutually inhibitory functioning between the VLPA and the TMN. For a thorough review of this system the reader is referred to Saper et al. Trends Neurosci 2001;24:726-31.