Sleep oscillations and psychiatric disorders

Abstract

Scalp-recorded EEG oscillations are rhythmic activities within a specific frequency range generated by underlying neuronal populations. In recent years, neuronal oscillations have been shown to be implicated in critical healthy brain functions, including memory, learning, and plasticity. Furthermore, numerous studies have established abnormal neural oscillations in neuropsychiatric conditions, thus suggesting the implication of oscillation-related underlying neuronal circuits in the neurobiology of those disorders. Sleep offers important advantages for investigating dysfunctions of brain circuits in neuropsychiatric patients. Sleep recordings minimize waking-related confounding factors, including fluctuation in attention, reduced cognitive ability, and presence of psychiatric symptoms. Additionally, the two main NREM sleep oscillations, slow waves and spindles, reflect the activity of complementary thalamocortical circuits. In this chapter we will describe the main characteristics of neuronal oscillations, including frequency and topography, with particular emphasis on slow waves and sleep spindles. We will then review the evidence for abnormal sleep oscillations in psychiatric disorders. Finally, we will discuss how these findings inform our current understanding of the neurobiology of brain disorders, and especially major depression and schizophrenia, and how future sleep studies may provide biological “signatures” to inform the diagnosis, prognosis, as well as treatment of psychiatric patients.