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Previous studies suggest that sleep allows us to recharge, or sleep is the brain's way to expel waste. Two recent studies provide evidence that sleep restores cellular homeostasis in the brain and allows us to forget less important events of the day.

The study was published Thursday in the journal Science. It suggests sleep enables a reset on the brain's synapses to enhance learning. Synapses are the part of the brain that stores memories.

It transmits signals between neurons that collect information when awake. Without sleep the brain may get overloaded with unnecessary information which may cause the brain not to function 100 percent of its potential.

The Guardian reported the researchers used a technique called serial block-face scanning electron microscopy to create high-resolution 3D images of almost 7,000 synaptic connections in two different regions of the cerebral cortex. It took them more than four years to complete the method.

According to Inquistr, the University of Wisconsin-Madison researchers observed four lab mice while they were asleep. Dr. Chiara Cirelli and Dr. Giulio Tononi examined thousands of images.  The synapses growth had decreased by an average of 18 percent. The larger synapses remained the same size, which suggests that sleep doesn't affect more important memories.

The theory has been dubbed as synaptic homeostasis. It suggests that synapses grow so much while people are awake.

The second study was similar and provided further evidence. Graham Diering of Johns Hopkins University and his team conducted multiple experiments on mice using two-photon imaging to view synaptic proteins in the mice's brains.

They have observed that the proteins had declined while the mice slept. It showed shrinkage in synapses during sleep. They were able to isolate the protein Homer1A. They compared the findings with genetically engineered mice injected with Homer1A and found no changes.

They trained both mice with mild electric shocks on a maze. Those injected with Homer1A protein had intrusive memories of the shocks.

Together these studies explain why sleep is important for mental function. Sleeping on it can help us think more clearly.