Individual sleep need, brain health and cognitive function - Anders Martin Fjell

Background 
Public health recommendations and clinical paradigms often treat sleep need as a rigid, universally applicable constant. However, this "one-size-fits-all" approach struggles to reconcile the acute neurocognitive deficits seen in laboratory sleep deprivation with observational data.

Objective
In this presentation, I will argue that individual sleep need is a dynamic, negotiable quantity regulated by ecological niches, motivational states, and adaptive plasticity rather than a hard-coded biological requirement.

Methods
We integrate cross-disciplinary evidence, including behavioral ecology, evolutionary modeling, and large-scale neuroimaging. Our empirical framework utilizes the Lifebrain consortium database, analyzing over 51,000 cross-sectional and 8,000 longitudinal MRIs to examine the purported causal link between sleep duration and brain atrophy.

Results 
We find no phenotypic or genotypic evidence that short sleep causes accelerated brain atrophy or structural decline in healthy adults. Cross-sectional "sweet spots" for maximal cortical thickness and cognitive performance converge around 6.5–7 hours, below many current recommendations. Furthermore, we demonstrate that humans and other species exhibit remarkable sleep flexibility; when sleep is reduced gradually in motivated, naturalistic settings, typical vigilance deficits are often mitigated or absent.

Conclusion 
These findings challenge "sleep essentialism" and the notion of a sleeplessness epidemic. We conclude that the brain's sleep-wake balance is highly conserved and adaptive, and that the evidence linking natural variation in sleep patterns to brain health is surprisingly weak. Future research and clinical guidelines should shift focus from rigid duration targets toward understanding individual variance in sleep need and the psychological and environmental factors that facilitate successful adaptation to sleep loss.