Effects of ageing on cortical neural dynamics and local sleep homeostasis in mice

Healthy ageing is associated with marked effects on sleep, including its daily amount and architecture, as well as the specific electroencephalogram (EEG) oscillations. Neither the neurophysiological underpinnings, nor the biological significance of these changes are understood, and crucially the question remains whether ageing is associated with reduced sleep need or a diminished capacity to generate sufficient sleep. Here we tested the hypothesis that ageing may affect local cortical networks, disrupting the capacity to generate and sustain sleep oscillations, and with it the local homeostatic response to sleep loss. We performed chronic recordings of cortical neural activity and local field potentials (LFP) from the motor cortex in young and older male C57BL/6J mice, during spontaneous waking and sleep, as well as during sleep after sleep deprivation. In older animals, we observed an increase in the incidence of non-rapid eye movement (NREM) sleep LFP slow waves and their associated neuronal silent (OFF) periods, while the overall pattern of state-dependent cortical neuronal firing was generally similar between ages. Furthermore, we observed that the response to sleep deprivation at the level of local cortical network activity was not affected by ageing. Our data thus suggest that the local cortical neural dynamics and local sleep homeostatic mechanisms, at least in the motor cortex, are not impaired during healthy senescence in mice. This indicates that powerful protective or compensatory mechanisms may exist to maintain neuronal function stable across the life span, counteracting global changes in sleep amount and architecture