This is what tends to happen during sleep

It remains a mystery why we sleep, whether it’s for saving energy, clearing away the waste present at the brain, or that need for animals to be safe and sound from predators and external factors. But a pair of new studies just might enrich the discussion further.

One paper, led by neuroscientists Chiara Cirelli and Giulio Tononi from the University of Wisconsin-Madison, found that mice synapses—connections between brain cells—shrunk by an average of 18 percent during sleep. These synapses then grew as the day went on, only to be pared back again at night time, Cirelli says.

To reach this conclusion, Tononi and Cirelli used serial block-face scanning electron microscopy, a state-of-the-art device that can capture snapshots of neurons in two parts of the cerebral cortex.

The researchers made a tiny incision in that brain region, which is responsible for memories, and scanned each layer, day and night.

Then, analyzing their thousands of images, they found key structural changes in the synapses at night, shrinking them, compared to their growth during the day time.

The second paper offers a biochemical explanation for this.

Researchers at John Hopkins University found that when mice fall asleep their synapses absorb a protein called homer1a.

It was this protein that instigated a weakening effect, loosening the connections between synapses that are built up by memories and information. 

Conversely, during the day time, harmorapa was pushed out of the synapses. 

And when the mice were given a stimulant equivalent to coffee,  was prevented from entering the synapses.  

The new papers, both published in the journal Science, come months after a Norwegian study used the first brain-imaging of synapses to suggest sleep breaks synapse connections. 

To investigate the subject, the team at the University of Freiburg monitored 20 students between 19 and 25 years old, all right-handed non-smokers, free of any mental disorder, drug abuse, or medication use.

In one experiment, the participants had a good night's sleep of about seven hours before being screened.

In the next, they stayed awake for 24 hours - playing games, cooking food, but not drinking caffeine - before undergoing the same test.

To screen them, the researchers zapped magnetic waves at the motor cortex - the brain region that controls movement - to trigger a twitch in the left hand.

They found the sleep-deprived participants barely needed any magnetic pulse to trigger a reaction.

That suggested their brain is more 'excitable' than those who are well-rested, and therefore the synapses - which connect brain neurons - are stronger.

Professor Christopher Nissen, the psychiatrist who led the study, then got the groups to carry out word-pair activities that rely on creating new memories.

In these tests, the sleep-deprived participants fared far worse than their well-rested peers.

Just one rough night of sleeplessness, Professor Nissen warned, blocks the brain from resetting, leaving the person foggy, slow and relatively unobservant for the rest of the day.

It suggested that without sleep the brain's synapses are saturated, tense and strong; filled with all the memories of the day. It makes us tetchy and unable to think clearly.

'Still we do not really know why we spend such a long time of our lives in this inactive state, so sleep must have a very important function,' Nissen explained.

'Otherwise it's just a very big mistake that evolution made.

'Our study highlights the importance of sleep, and the notion that sleep is a highly active brain process, not a waste of time.'