Circuits and components of delta wave regulation

Abstract

Sleep is vital and the deepest stages of sleep occur within Non-rapid-eye-movement sleep (NREM), defined by high electroencephalographic power in the delta (~0.5-4 Hz) wave frequency range. Delta waves are thought to facilitate a myriad of physical and mental health functions. This review aims to comprehensively cover the historical and recent advances in the understanding of the mechanisms orchestrating NREM delta waves. We discuss a complete neurocircuit - focusing on one leg of the circuit at a time - and delve deeply into the molecular mechanistic components that contribute to NREM delta wave regulation. We also discuss the relatively localized nature in which these mechanisms have been defined, and how likely they might generalize across distinct sensory and higher order modalities in the brain.

Keywords: Brain waves; Delta waves; Electroencephalography; Neurocircuitry; Non-rapid-eye-movement sleep; Sleep.

Fig. 1.

Model diagram of the thalamocortical circuitry driving delta waves during NREM sleep. Glutamatergic thalamocortical (TC) relay neurons (orange) project to the cortex and receive glutamatergic inputs returning from the neocortex. The thalamic reticular nucleus (TRN) does not project to the cortex. Instead, the TRN modulates cortical activity via the TC relay neurons, by providing them with their primary source of inhibitory drive. Both major types of thalamic population shown here are defined by their expression of native specialized subtypes of channels and receptors (expanded notes), providing the cells with electrophysiologic mechanisms to generate (TC relay) and promote (TRN) NREM delta waves.