Is being alone restful or corrosive? Work from Yu Hayashi's laboratory at the University of Tokyo suggests the answer depends on who you are. The team studied two mouse strains with different genetic backgrounds, first establishing social hierarchies, then housing animals as neighbours able to see and smell but not touch one another, and finally moving them into complete isolation while recording brain waves to track sleep.
Under neighbour housing, dominant and subordinate mice slept indistinguishably in both strains. Isolation changed the picture, but only in one genetic background. Mice of the F1 strain barely altered their sleep when alone. Dominant B6 mice, by contrast, slept better in isolation, possibly relieved of the burden of guarding territory, while subordinate B6 mice showed more REM sleep of poorer quality, consistent with losing the security of a nearby companion.
Published in Scientific Reports, the findings indicate that the consequences of solitude for sleep are not universal but contingent on environment, social standing and genetic background acting together. The authors are careful to frame the work as a starting point rather than a verdict on human experience: loneliness in people is longer-lasting and far more complex. Even so, the study offers a tractable laboratory model for dissecting the biology that links social life, stress and sleep.