Sleep has profound importance in our lives, such that we spend a considerable proportion of our time engaging in it. Sleep enables the body, including the brain, to recover metabolically, but contemporary research has been moving to focus on the active rather than recuperative role that sleep has on our brain and behaviour.
Sleep is composed of several distinct stages. Two of these, slow-wave (or deep) and REM sleep, reflect very different patterns of brain activity, and have been related to different cognitive processes.
Slow-wave sleep is characterised by synchronised activity of neurons in the neo-cortex firing at a slow rate, between 0.5 and three times per second.