Researchers used to think that sleep had little to do with forming memories. The relationship between memory and sleep was thought to be more about the survival of the fittest: Only the strongest memories survive, and the rest forgotten.
But a new understanding has slowly been developing in the field of neuroscience. “Sleep is for strengthening memories and changing them. Sleep does many more things than just allowing the strongest memories. It can even rescue the most weak memories,” says Sidarta Ribeiro, a Brazilian neuroscientist who directs the Brain Institute at the Federal University of Rio Grande do Norte.
In a new paper published in the journal PLoS Computation Biology, Ribeiro describes his work that he says pushes the envelope of this idea. Using lab rats, they investigated a process called long-term potentiation (LTP)–a kind of electrical “memory” that involves long-lasting strengthening of neuron synapses based on recent patterns of activity–as it occurs during sleep. In rats that had recently been exposed to a novel experience while they were awake, they showed the rats exhibited LTP activity as they were allowed to enter REM sleep, the phase of deep sleep that is usually associated with dreaming. But rats that didn’t get exposed to a new activity showed no signs of LTP.
By feeding this experimental data into a brain model, Ribeiro says that LTP during sleep can not only strengthen connections between neurons, it also can “re-organize” the pattern of connections. In other words, he says, sleep may be not only for forgetting, but it’s also for forming memories–and also for transforming them, a process he links to creativity in humans. Conversely, a lack of LTP leads to memory erasure.
The study is based on data with rats, so Ribeiro cautions against translating the findings directly to humans. However, he thinks they may have implications for how sleep–especially short naps–affect human memory and creativity. A power nap that is too short for a full REM sleep cycle, for example, might help rejuvenate ourselves and consolidate our memories. But a slightly longer nap may be needed to really spark the emergence of new ideas.
“We know that some types of naps really restore fatigue. Some kinds of naps really enhance cognition,” he says. “It may be that the longer nap is better for tasks in which you need to be creative.”