Throughout the day, the human brain absorbs a torrent of knowledge, processes the information, and learns, before "switching off" over night. New research explains this process in action. Microscopic images of synapses - the junction between two nerve cells - have been shown to expand with daytime stimulation and shrink with sleep, thus resetting the brain ready for the next day.

Scientists at the University of Wisconsin School of Medicine and Public Health conducted a 4-yearstudy that demonstrates the "synaptic homeostasis hypothesis" (SHY) functioning.

Results of the study were published in the journalScience.

SHY is a theory proposed by Dr. Chiara Cirelli and Dr. Giulio Tononi, both of the Wisconsin Center for Sleep and Consciousness. Cirelli and Tononi speculate that sleep is the price we must pay for brains that are pliable and able to learn new things repeatedly.

Constant stimulation of the synapse during wakeful hours results in it growing stronger and larger, and it is thought that this expansion plays a key role in memory and learning. To ensure that the synapse does not become saturated and neural signaling and memories obliterated, SHY indicates that this growth must be counterbalanced.

Sleep is thought to be the perfect counterbalance and ideal time for the process of renormalization. During sleep, people are less aware of the "here and now" and can block out the external world, which may balance and restore the synapse.

As synapses become stronger and more efficient they get bigger. In contrast, as they weaken, the synapses shrink in size.

Cirelli and Tononi aimed to test their theory by analyzing whether the size of the synapses alters between sleeping and waking hours.