Researchers have found that while we sleep, our brains are busy processing our waking experiences. A process called ‘offline replay’, they say that the process may help people organize their experiences and solidify new memories.
For the study, the researchers recruited two participants with tetraplegia, a condition in which people are unable to move the upper and lower parts of their body voluntarily. As they had already been involved in another clinical trial, both patients already had small sensors known as microelectrode arrays implanted in their cerebral cortexes.
During the research, the scientists asked the participants to take a nap before and after playing a sequence-copying game that lit up four panels in various sequences for the player to repeat. As the participants had no control over their upper bodies, they used their minds to move the cursor. The researchers recorded their brain activity as they napped, played the game and napped again.
In the end, they found that both participants fired neurons in similar ways while playing the game and during their naps afterwards. They say that this indicates that the participants' brains continued to play the game at the neuronal level as they slept.
"We were certainly surprised to see replay in the human brain, even though it's what we were expecting given the animal literature," says Besta Jarosiewicz, one of the study’s authors. "To make sure what we were seeing was real, we did a series of sanity checks, or controls, to make sure the result wasn't an artifact of something trivial we were overlooking."
Confirming their findings with controls, the researchers concluded that offline reply likely solidifies memories by gradually incorporating them in the neocortex- the part of the brain responsible for processing sensory information and making decisions.