The resilient brain and the guardians of sleep: new perspectives on old assumptions

Resilience is the capacity of a system, enterprise or a person to maintain its core purpose and integrity in the face of dramatically changed circumstances. In human physiology, resilience is the capacity of adaptively overcoming stress and adversity while maintaing normal psychological and physical functioning. In this review, we investigate the resilient strategies of sleep. First, we discuss the concept of brain resilience, highlighting the modular structure of small-world networking, neuronal plasticity and critical brain behaviour. Second, we explore the contribution of sleep to brain resilience listing the putative factors that impair sleep quality and predict susceptibility to sleep disorders. The third part details the manifold mechanisms acting as guardians of sleep, i.e., homeostatic, circadian and ultradian processes, sleep microstructure (K-complexes, delta bursts, arousals, cyclic alternating pattern, spindles), gravity, muscle tone and dreams. Mapping and pooling together the guardians of sleep in a dynamic integrated framework might lead towards an objective measure of sleep resilience and identify effective personalized strategies (biological, pharmacological, behavioral) to restore or protect the core properties of healthy sleep.