The prevailing notion is that our sleep habits are hard-wired in some way, or genetically determined, and that all animals, including humans, have to perform a certain, non-negotiable amount of sleep every day. To this end, major research efforts in the last few decades have been focused on investigating the underlying biology of "sleep need", targeting a broad range of molecules, physiological processes or brain areas. However, according to DPAG’s lead sleep researcher Associate Professor Vladyslav Vyazovskiy: “What we tend to forget is that wakefulness and sleep are defined, by and large, by the interaction of the organism with its environment. Consistently, evidence accumulates that "sleep need" can vary greatly depending on external conditions or other homeostatic drives, in addition to the genetic makeup.”
A new study from the Vyazovskiy lab supports this view. The study, led by DPhil student Linus Milinski, addresses whether changes in an animal's environment would affect its wake behaviours, and whether this, in turn, would affect its subsequent sleep. The team’s main experiment trained mice on a simple ‘nose poke’ task, using a touchscreen operant chamber. Unexpectedly, the animals sometimes performed the task, voluntarily, for many hours in a row, even during the day, which is a habitual sleep time in laboratory mice. Professor Vyazovskiy said: “We therefore hypothesised that certain wake behaviours may slow down the accumulation of ‘tiredness’ during continuous waking, resulting in a reduced sleep need.” Consistent with this hypothesis, the researchers found that during subsequent sleep, EEG slow waves, an established marker of homeostatic sleep need, were markedly lower after wake dominated by a simple task performance, when compared to wake spent in an enriched environment.
While further research is required to further our understanding of how sleep is affected by wake activities, the study concludes that wake ‘quality’ is important for subsequent sleep, and that the effect of environmental factors and motivation are key factors to consider in sleep studies. According to Professor Vyazovskiy: “Arguably, the time spent awake and specific wake activities are determined, to a large extent, by environmental contingencies, both predictable and unpredictable. Therefore, changes in sleep habits, produced by our experimental manipulations, can arise primarily from an altered relationship between the organism and the environment. In this respect, our study makes a strong case that studying sleep in an ecological context can provide new insights, beyond those obtained in standard laboratory conditions.”
The full paper “Waking experience modulates sleep need in mice”, in collaboration with Professor David Bannerman from the Department of Experimental Psychology, is available to read in BMC Biology.