Figure 1.

A schematic to demonstrate the complexity of the interaction between sleep (orange) and ageing (grey) and the important influences of both intrinsic factors (blue) such as genes and extrinsic factors (green) including the environment, specific waking experiences and ecological factors. Sleep undergoes progressive changes across the lifespan, which represents a combination of programmed ageing as well as the accumulation of damage resulting from environmental stressors. In addition, ageing influences the interaction of the organism with the environment, and thus it alters the role of ecological factors in sleep regulation. Sleep is a complex process regulated by local cellular/synaptic processes and global state control. Likewise, ageing manifests both at the level of local phenomena such as the occurrence of cellular stress or loss of synaptic connectivity as well as global changes in physiological functions and behaviour. Therefore both sleep and ageing must be considered at the various levels of organisation, from local to global mechanisms (yellow), as well as their interaction, in order to be fully understood.