Sleep Sleep plays an important role in brain health. Humans spend about one-third of each day sleeping, and sleep is key to brain health. Sleep plays an important role in the function of the brain, the immune system and many other systems in the body. Sleep keeps you sharp, focused and able to make thoughtful decisions. While different age groups require different amounts of sleep, the general recommendation is around six to seven hours a night. This consistent, restful sleep gives your brain time to dispose of metabolic waste and optimise memory.