Cholinergic switch between two types of slow waves in cerebral cortex

TL;DR

This study identifies two distinct types of slow waves in the cerebral cortex, elucidating their neural mechanisms and implications for memory, with a focus on differences between sleep and anesthesia.

Contribution

It reveals a neuromodulatory switch between slow wave types driven by cholinergic activity, linking slow-wave dynamics to memory processes and neurological conditions.

Findings

Two types of slow waves identified in sleep and anesthesia

Cholinergic modulation can switch between slow wave types

Different slow wave types have distinct effects on memory

Abstract

Sleep slow waves are known to participate in memory consolidation, yet slow waves occurring under anesthesia present no positive effects on memory. Here, we shed light onto this paradox, based on a combination of extracellular recordings in vivo, in vitro, and computational models. We find two types of slow waves, based on analyzing the temporal patterns of successive slow-wave events. The first type is consistently observed in natural slow-wave sleep, while the second is shown to be ubiquitous under anesthesia. Network models of spiking neurons predict that the two slow wave types emerge due to a different gain on inhibitory vs excitatory cells and that different levels of spike-frequency adaptation in excitatory cells can account for dynamical distinctions between the two types. This prediction was tested in vitro by varying adaptation strength using an agonist of acetylcholine receptors, which demonstrated a neuromodulatory switch between the two types of slow waves. Finally, we show that the first type of slow-wave dynamics is more sensitive to external stimuli, which can explain how slow waves in sleep and anesthesia differentially affect memory consolidation, as well as provide a link between slow-wave dynamics and memory diseases.