Summary: Scientists have proposed a new model that explains how different sleep stages may support problem solving and creativity. The research suggests that non-REM sleep organizes and categorizes memories, while REM sleep enables the brain to form surprising connections between those categories.
Source: Cell Press.
Sleep supports creative thinking, but the specific contributions of REM and non-REM sleep have been uncertain. In a new Opinion article published May 15 in Trends in Cognitive Sciences, researchers propose a testable model describing how the alternating cycles of non-REM and REM sleep could work together to enhance creative problem solving and insight.
“Imagine you have a puzzle and you already possess the facts needed to solve it, but you remain stuck because your memories aren’t being linked in the right way,” says Penny Lewis, the study’s first author and a professor at the Cardiff University School of Psychology. “You need to restructure existing memories—form new associations and integrate pieces that weren’t previously connected.”
Behavioral studies indicate that such restructuring often happens during sleep. Drawing on experimental evidence and physiological observations, Lewis and colleagues outline a mechanism in which non-REM sleep and REM sleep perform complementary roles. According to their model, non-REM sleep favors organizing experiences into coherent categories or schemas, while REM sleep promotes the spontaneous recombination of stored information, allowing novel analogies and creative leaps to emerge.
Previous work shows that memories initially encoded by the hippocampus are replayed during non-REM sleep. As similar experiences reappear, cortical networks detect shared structure and gradually extract generalized information. Lewis and co-authors suggest the hippocampus actively controls which memory traces are replayed during non-REM, preferentially reinstating them in clusters that share themes or features. This selective replay helps the brain build organizing frameworks—schemas—that summarize the gist of related memories.
REM sleep appears to operate differently. During REM, communication between the hippocampus and cortex is reduced, and the cortex becomes more autonomous. The research team proposes that this state frees cortical circuits to replay stored material in unconventional combinations, irrespective of their original similarity. In addition, REM-associated ponto-geniculo-occipital (PGO) waves stimulate random activations across cortical regions, which can trigger the co-activation of elements drawn from distinct schemas. When a salient problem or memory trace is replayed alongside a randomly activated but partially similar memory, a novel connection can form—one that may provide the sudden insight needed to solve a problem.
To illustrate how these processes could yield a creative breakthrough, Lewis points to Ernest Rutherford’s iconic model of the atom, inspired by the solar system. Under the proposed framework, Rutherford’s memories about atomic observations and about planetary motion could have been organized into separate schemas during non-REM sleep. Later, during REM sleep, a cortical replay of atomic details might have been paired with a spontaneously activated memory of the solar system, allowing him to perceive the structural analogy and apply it productively.
“Our goal is to formalize this model so it can be empirically tested,” Lewis adds. With a multi-year grant in place, her team is already designing experiments to probe the roles of hippocampal-cortical replay, selective replay during non-REM, and the combinatorial dynamics of REM sleep. The researchers hope these tests will clarify how sleep stages together support the reorganization of knowledge and the emergence of creative solutions.
Funding: The authors acknowledge support from the European Research Council, EPSRC, Cardiff University, UCLA, and the National Institutes of Health.
Source: Kelly McClorey – Cell Press
Publisher: Organized by NeuroscienceNews.com.
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Original Research: Open access research for “How Memory Replay in Sleep Boosts Creative Problem-Solving” by Penelope A. Lewis, Günther Knoblich, and Gina Poe in Trends in Cognitive Sciences. Published May 14, 2018.
doi: 10.1016/j.tics.2018.03.009
Suggested citation formats are provided by the publisher for scholarly use. Please refer to the original article and journal for citation details.
Abstract
Corticoinsular circuits encode subjective value expectation and violation for effortful goal-directed behavior
Sleep is widely recognized as beneficial for creative problem solving, but debate continues over the specific roles of REM and non-REM sleep. Behavioral evidence increasingly supports the view that memory replay during non-REM sleep is critical for extracting abstract gist and rules from related experiences. In contrast, the heightened excitation, plasticity, and cortical connectivity characteristic of REM sleep create favorable conditions for forming novel, unexpected associations among cortical representations.
The authors propose that the iterative alternation of non-REM and REM sleep across the night enhances complex analogical reasoning: non-REM replay consolidates and organizes memories into schemas, while REM replay and spontaneous cortical activations allow these schemas to be recombined in novel ways. This interleaving potentially facilitates the restructuring of knowledge required for creative insight. The paper outlines a hypothetical computational model to make these ideas explicit and experimentally testable.