Table 1. The biological functions of sleep.

Adapted with permission from Mader EC Jr and Mader AC [3].

The four main categories of sleep functions
Metabolic and functional recovery
	Energy balance: energy conservation by lowering metabolic rate and downscaling sensory and motor processes; restoration of energy stores
	Functional recovery: synthesis of proteins involved with neurotransmitter function, transport, membrane trafficking, lipid and myelin metabolism
	Waste removal: slowing metabolite buildup to enable cellular waste removal; increased glymphatic clearance
Defense and response to injury
	Protective sleep behavior: sleeping` at the right time in a secure place increases survival chances
	Inflammatory and immune response: acute phase response to infection, inflammatory cytokine production (e.g., interleukins, TNF) and immuno-regulation
	Healing: promotes healing directly or indirectly via restorative, immune, and other functions
Neurodynamics and neuroplasticity
	Learning and memory:  strengthening of synapses and synaptic homeostasis to renormalize synapses in preparation for waking experience
	Developmental plasticity: rapid brain development and neurogenesis
	Neurodynamic homeostasis: for optimal neural signaling in wakefulness
Timing of biological processes
	Programmed sleep behavior: reduces predation risk; enhances foraging success and reproductive capacity during wake periods
	Platform for synchronizing diverse processes: allows disparate biological processes to operate in harmony to achieve optimal health