What does the brain do during sleep?

7th Feb 2017

Researchers have found from microscopic pictures of the insides of mice brains that synapses grow strong during stimulation of daytime, then shrink by 18% during sleep, creating room for learning the next day.

This research offers proof to support the 'synaptic homeostasis hypothesis' (SHY). The hypothesis states that sleep is the price we pay for brains that are plastic and able to learn new things.

A synapse repeatedly used during waking grows in strength, which is important for learning and memory. According to SHY, the growth needs to be balanced to avoid saturation of synapses and loss of memories. Sleep is believed the best time for this as less attention is needed to the external world. 

In the study, to test the SHY hypothesis, the researchers used high spatial resolution method of 3D microscopic pictures. They were able to reconstruct 6,920 synapses and measure their size. They found that when the mice had had 6-8 hours of sleep, the synapses reduced on average by 18% in size. This scaling occurred in 80% of the synapses they measured.

This therefore confirms SHY's predictions, and identifies genes important for this process. Further research to be done is on the effect of lack of sleep on these synapses. 

To read the full article, please go to Science journal website