We spend almost a third of our lives sleeping , and perhaps many times you have wondered if this waste of time makes any sense. Well, sleep is the price we pay for having a plastic brain, capable of learning new things throughout life.
During the night rest our mind presses the reset button and does a good cleaning that will allow us to be fresh the next day. This is not difficult to understand, but how does this process happen at a physiological level? After four years of research, a team of scientists shows us high-resolution images of laboratory mouse brains in which we can directly observe the phenomenon.
These images, obtained by electron microscopy in 3D with high spatial resolution, suggest to us what happens in our own brain every day: synapses – junction areas between two neurons – get fat during the day, but at night they can lose up to 20% of its size. It is thus a visual test of what the team calls the “neuronal homeostasis hypothesis”: neurons that are activated during the day increase in size, and this increase appears to play an important role in learning and memory.
However, this growth needs to be balanced, because if all our brain cells were to increase unlimitedly in size, there would be a collapse in the transmission of neuronal signals. Sleep is the perfect time to carry out this normalization process, since during those hours we have to pay less attention to what is happening in the outside world.
To verify this, the researchers, who publish their work in the journal Science , photographed, reconstructed and analyzed two different areas of the cerebral cortex of laboratory mice, reconstructing and measuring almost 7,000 synapses.
The results revealed that, indeed, a few hours of sleep results in an 18% decrease in the mean size of the synapses. These changes occurred in the two brain areas studied and were proportional to the size of the synapses .
“Our work shows that, in unequivocal ultrastructural terms, the balance in the size of synapses is altered during wakefulness and restored during sleep,” explains Chiara Cirelli of the Wisconsin Sleep and Wake Center. “Extrapolating the results to what happens in a human brain, this means that every night trillions of synapses in our cerebral cortex would be losing almost 20% of their size during the day”, concludes Giulio Tononi, another of the participants in the study.
Photos: Wisconsin Sleep and Wake Center
