Researchers at NYU Grossman School of Medicine led the study, which focuses on how neurons, a type of brain cells, "fire"—that is, cause changes in the balance between their positive and negative charges—to transfer electrical signals that encode memories. The hippocampus is a part of the brain where large groups of neurons fire in rhythmic cycles. These signals are created within milliseconds of one another and can encode complicated information.
New studies have discovered that daytime events followed by five to twenty sharp wave-ripples are highly likely to be replayed during sleep; therefore, they are consolidated into permanent memories. Events followed by few or no wave-ripples fail to form long lasting memories.
Sharp wave-ripples only appear in the idle moments just before or after when we are actively exploring sensory information or moving. As we sleep, those same cells fire rapidly for memories that are retained, "playing back the recorded event thousands of times per night." The procedure fortifies the bonds among the participating cells.
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