Spatial patterns of neuronal activity in rat cerebral cortex during non-rapid eye movement sleep

TL;DR

This study shows that brain activity in rats during non-REM sleep is not uniform but instead varies across different regions of the cortex.

Contribution

The study introduces thallium-autometallography to reveal spatially diverse neuronal activity patterns during NREMS in unrestrained rats.

Findings

Cortical activity during NREMS is spatially heterogeneous, not uniform.

Infragranular layer activation is more prevalent during NREMS.

Adjacent neuronal groups show significant differences in metabolic activity.

Abstract

It is commonly assumed that cortical activity in non-rapid eye movement sleep (NREMS) is spatially homogeneous on the mesoscopic scale. This is partly due to the limited observational scope of common metabolic or imaging methods in sleep. We used the recently developed technique of thallium-autometallography (TlAMG) to visualize mesoscopic patterns of activity in the sleeping cortex with single-cell resolution. We intravenously injected rats with the lipophilic chelate complex thallium diethyldithiocarbamate (TlDDC) during spontaneously occurring periods of NREMS and mapped the patterns of neuronal uptake of the potassium (K+) probe thallium (Tl+). Using this method, we show that cortical activity patterns are not spatially homogeneous during discrete 5-min episodes of NREMS in unrestrained rats—rather, they are complex and spatially diverse. Along with a relative predominance of infragranular layer activation, we find pronounced differences in metabolic activity of neighboring neuronal assemblies, an observation which lends support to the emerging paradigm that sleep is a distributed process with regulation on the local scale.

The online version of this article (doi:10.1007/s00429-014-0867-9) contains supplementary material, which is available to authorized users.

Figures