“You can forget in a smart way,” Dr. Tononi said.
Other researchers cautioned that the new findings weren’t definitive proof of the synaptic homeostasis hypothesis.
Marcos G. Frank, a sleep researcher at Washington State University in Spokane, said that it could be hard to tell whether changes to the brain at night were caused by sleep or by the biological clock. “It’s a general problem in the field,” he said.
Markus H. Schmidt, of the Ohio Sleep Medicine Institute, said that while the brain might prune synapses during sleep, he questioned whether this was the main explanation for why sleep exists.
“The work is great,” he said of the new studies, “but the question is, is this a function of sleep or is it the function?”
Many organs, not just the brain, seem to function differently during sleep, Dr. Schmidt pointed out. The gut appears to make many new cells, for example.
Dr. Tononi said that the new findings should prompt a look at what current sleeping drugs do in the brain. While they may be good at making people sleepy, it’s also possible that they may interfere with the pruning required for forming memories.
“You may actually work against yourself,” Dr. Tononi said.
In the future, sleep medicines might precisely target the molecules involved in sleep, ensuring that synapses get properly pruned.
“Once you know a little bit of what happens at the ground-truth level, you can get a better idea of what to do for therapy,” Dr. Tononi said.