Most people know it from experience: After so many hours of being awake, your brain feels unable to absorb any more—and several hours of sleep will refresh it.Now new research from the University of Wisconsin School of Medicine and Public Health clarifies this phenomenon, supporting the idea that sleep plays a critical role in the brain’s ability to change in response to its environment. This ability, called plasticity, is at the heart of learning.
Reporting in the Jan. 20, 2008, online version of Nature Neuroscience, the UW-Madison scientists showed by several measures that synapses — nerve cell connections central to brain plasticity — were very strong when rodents had been awake and weak when they had been asleep.
The new findings reinforce the UW-Madison researchers’ highly-debated hypothesis about the role of sleep. They believe that people sleep so that their synapses can downsize and prepare for a new day and the next round of learning and synaptic strengthening.
The human brain expends up to 80 percent of its energy on synaptic activity, constantly adding and strengthening connections in response to all kinds of stimulation, explains study author Chiara Cirelli, associate professor of psychiatry.
Given that each of the millions of neurons in the human brain contains thousands of synapses, this energy expenditure “is huge
Source: National Institutes of Health , University of Wisconsin-Madison
