What role do the stages of sleep play in forming memories? “We’ve known for a long time that useful learning happens during sleep,” says University of Pennsylvania neuroscientist Anna Schapiro. “You encode new experiences while you’re awake, you go to sleep, and when you wake up your memory has somehow been transformed.”
Yet precisely how new experiences get processed during sleep has remained mostly a mystery. Using a neural network computational model they built, Schapiro, Penn Ph.D. student Dhairyya Singh, and Princeton University’s Kenneth Norman now have new insight into the process.
In research published in the Proceedings of the National Academy of Sciences, they show that as the brain cycles through slow-wave and rapid-eye movement (REM) sleep, which happens about five times a night, the hippocampus teaches the neocortex what it learned, transforming novel, fleeting information into enduring memory.
“This is not just a model of learning in local circuits in the brain. It’s how one brain region can teach another brain region during sleep, a time when there is no guidance from the external world,” says Schapiro, an assistant professor in Penn’s Department of Psychology. “It’s also a proposal for how we learn gracefully over time as our environment changes.”
Broadly, Schapiro studies learning and memory in humans, specifically how people acquire and consolidate new information. She’s long thought that sleep played a part here, something she and her team have been testing in a lab, recording what happens in the brain as participants sleep.
Her team also builds neural network models to simulate learning and memory functions. For this work specifically, Schapiro and colleagues built a neural network model composed of a hippocampus, the brain’s center for new memories, tasked with learning the world’s day-to-day, episodic information, and the neocortex, responsible for facets like language, higher-level cognition, and more permanent memory storage. During simulated sleep, the researchers can watch and record which simulated neurons fire when in these two areas, then analyze those activity patterns.
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