The debate in sleep science has gone on for a generation. In short … why do we sleep?
Psychiatrists Chiara Cirelli and Giulio Tononi of the Wisconsin Center for Sleep and Consciousness suggested back in 2003 that sleep is the price we pay for brains that are able to keep learning new things.
A few years ago, they went all in on a four-year research effort that could show direct evidence for their theory.
The result, published last year, offered direct proof of their hypothesis. Cirelli expanded on the research recently at the annual meeting of the American Association for the Advancement of Science.
Striking electron-microscope pictures from inside the brains of mice suggest what happens in our own brain every day: Our synapses – the junctions between nerve cells – grow strong and large during the stimulation of daytime, then shrink by nearly 20 percent while we sleep, creating room for more growth and learning the next day.
A large team of researchers sectioned the brains of mice and then used a scanning electron microscope to photograph, reconstruct, and analyze two areas of cerebral cortex. They were able to reconstruct 6,920 synapses and measure their size.
The team deliberately did not know whether they were analyzing the brain cells of a well-rested mouse or one that had been awake. When they finally “broke the code” and correlated the measurements with the amount of sleep the mice had during the six to eight hours before the image was taken, they found that a few hours of sleep led on average to an 18 percent decrease in the size of the synapses. These changes occurred in both areas of the cerebral cortex and were proportional to the size of the synapses.
For Cirelli, the study was a big gamble that paid off. But she’s not resting on her laurels. Her lab is now looking at new brain areas, and at the brains of young mice to understand the role sleep plays in brain development.