Study describes offline replay experienced while the brain is in a sleep phase

During the onset of sleep, the brain may not go offline but instead could be putting together new memories through a process known as an offline replay, according to new research published in Cell Reports.

In rodents, the process of offline replay occurs when the brain plays back neural firing patterns when in a stage of sleep. In the study, researchers tested if this process occurs in the brains of humans, relative to their experimentation of rodents.

The new findings were achieved by testing two participants who received implants with intracortical microelectrode arrays. They were instructed to nap prior to and after participating in a sequence-copying game, while researchers documented any change of activity of large groups of individual neurons in the brains.

“Here, we test for replay in the human brain by recording spiking activity from the motor cortex of two participants who had intracortical microelectrode arrays placed chronically as part of a brain-computer interface pilot clinical trial,” the findings read.

“Participants took a nap before and after playing a neurally controlled sequence-copying game that consists of many repetitions of one repeated sequence sparsely interleaved with varying control sequences.”

“Both participants performed repeated sequences more accurately than control sequences, consistent with learning. We compare the firing rate patterns that caused the cursor movements when performing each sequence to firing rate patterns throughout both rest periods,” the findings also stated.

From their assessment of both participants, researchers attested that the same neuronal firing patterns were evident during and after the span of participation in the gaming sessions.

Essentially, the neuronal activity suggests that the participants were still contributors in the session even after they were asleep — a first-of-its-kind discovery made in the brains of humans.

“Correlations with repeated sequences increase more from pre to post-task rest than do correlations with control sequences, providing direct evidence of learning-related replay in the human brain,” the study concluded.

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