“And He (Allah) it is Who has made the night a covering for you, and Who has made sleep for rest, and has made the day for rising up.” (Holy Quran 25:48)
Why we sleep remains one of the big mysteries of science. Allah has told us that sleep is for rest while the day is for activity. What about sleep makes it a period of rest? Is it simply the reduced respiration and heart rate that is needed for “rest”? Or is there some extra changes that need to occur during this period of sleeping?
Recent research has provided evidence for what our mother’s have always known: sleep is needed to learn. A new model that explains the function of sleep is called the synaptic homeostasis hypothesis. This model suggests that when we are awake the nerve cells in our brains are actively making new connections with other nerve cells. These connections are what allow us to learn and adapt. However, there is a limit on the number and overall size of connections the brain can handle, being limited by available space and supplies (building block, nutrients and energy). Eventually, we would reach a point where we could make no new connections and we would stop learning. This is where sleep plays an important function. The hypothesis suggests that when we sleep all (or almost all) of these new neuronal connections will shrink in size while retaining their connections to other nerve cells. This allows you keep the new connections, ie remember, while still reducing the overall energy demand.
Using fruit flies as a model, Bushey et al. (2011) were able to show that the more the flies learned (interacted with other flies vs. isolated), the more new connections the flies made. Furthermore, flies that were sleep deprived after “learning” retained their connections, but the connections were as large as they were right after learning and did not shrink. These flies had a huge energy demand. In addition, flies that engaged in the learning activity that were then moved to an isolated environment slept more during the day and night than the flies that did not learn (kept in isolation throughout the experiment).
In other words, the more you learn, the more your brain needs sleep.