Summary: Age related sleep disruptions are not due to alterations in activity of individual neurons as previously believed, researchers report.
The brain maintains its ability to generate local neural oscillations during sleep throughout the lifespan, according to a study of young and old mice published in Journal of Neuroscience. The research indicates that age-related disruptions in sleep and associated large-scale brain activity, are not due to changes in the activity of individual neurons.
Vladyslav Vyazovskiy and colleagues recorded neural activity from deep layers of the motor cortex of groups of mice at different stages of life: early adulthood (5 months), late adulthood (12 months) and old age (24 months). The old age mice in this study are estimated to correspond to an age of roughly 70-years in humans.
The researchers did not find any major differences in the cortical neural activity during sleep across the three age groups. All mice also showed similar effects of sleep deprivation on local sleep oscillations in the neocortex.
These findings contrast with previous studies both in mice and humans showing that ageing is associated with a reduced capacity to generate deep sleep, and highlight the need to consider activity at the level of individual neurons, in addition to the whole-brain view, in order to fully understand the effects of ageing on sleep.
Funding: Biotechnology and Biological Sciences Research Council, Eli Lilly, Wellcome Trust, Medical Research Council, John Fell OUP Research Fund funded this study.
Source: David Barnstone – SfN
Publisher: Organized by NeuroscienceNews.com.
Image Source: NeuroscienceNews.com image is in the public domain.
Original Research: Abstract for “Effects of ageing on cortical neural dynamics and local sleep homeostasis in mice” by Laura E McKillop, Simon P Fisher, Nanyi Cui, Stuart N Peirson, Russell G Foster, Keith A. Wafford and Vladyslav V Vyazovskiy in Journal of Neuroscience. Published online March 28 2018.
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.
The biological significance of age-dependent changes in sleep is unknown, but may reflect either a diminished sleep need or a reduced capacity to generate deep sleep stages. Since ageing has been linked to profound disruptions in cortical sleep oscillations, and since sleep need is reflected in specific patterns of cortical activity, we performed chronic electrophysiological recordings of cortical neural activity during waking, sleep and after sleep deprivation from young and older mice. We found that all main hallmarks of cortical activity during spontaneous sleep and recovery sleep after sleep deprivation were largely intact in older mice, suggesting that the well described age-related changes in global sleep are unlikely to arise from a disruption of local network dynamics within the neocortex.