Sleeping shrinks the brain’s neural connections, to allow growth: Study
06 Feb 2017
Sleep allows the brain to shrink neural connections according to new research that examined subtle changes in the brain during sleep.
The researchers found that sleep provided a time when the brain's synapses - the connections among neurons shrunk back by nearly 20 per cent. The synapses rested during the time and prepared for the next day, when they would grow stronger while receiving new input - that is, learning new things, the researchers said.
Scientists added that without this reset, called "synaptic homeostasis," synapses could become overloaded and burned out, like an electrical outlet with too many appliances plugged in to it.
"Sleep is the perfect time to allow the synaptic renormalization to occur … because when we are awake, we are 'slaves' of the here and now, always attending some stimuli and learning something," said study co-author Dr Chiara Cirelli of the University of Wisconsin-Madison Center for Sleep and Consciousness.
"During sleep, we are much less preoccupied by the external world … and the brain can sample [or assess] all our synapses, and renormalize them in a smart way," Cirelli told Live Science.
Cirelli and her colleague, Dr Giulio Tononi also of the University of Wisconsin-Madison, proposed the synaptic homeostasis hypothesis (SHY) in 2003.
Cirelli and Tononi now had direct visual evidence of SHY after observing the shrinking of synapses in mice, as the animals slept, in an intricate experiment that spanned four years. The researchers described their findings on Thursday in the journal Science.
Tononi and Cirelli used serial block-face scanning electron microscopy, a state-of-the-art device capable of capturing snapshots of neurons in two parts of the cerebral cortex.
They made a tiny incision in that brain region, which was responsible for memories, and scanned each layer, day and night.
On analysis of thousands of images, they found key structural changes in the synapses at night, shrinking them, while they identified growth during the day time.
