Abstract:

Memory reorganization is a necessary step in creative problem-solving. Sleep boosts creative problem-solving by promoting memory reorganization. Studies have shown that rapid eye movement (REM) sleep mainly facilitates novel associations, which occur mainly in the neocortex, while non-rapid eye movement (NREM) sleep facilitates the abstraction of rules, the formation of relational memory, and the integration of memories, which occur mainly in the hippocampus. Although the effect of sleep on creative problem-solving has been documented in most studies, there are still studies that have not yielded positive results. For example, firstly, aging is often characterized by substantial changes in sleep architecture, which results in sleep can not significantly promote creative problem-solving in older adults. Secondly, when memories are reactivated during sleep, the effect of sleep on creative problem-solving are enhanced, compared to sleep without manipulating memories. Thirdly, when facing with thinking set, it is necessary to decompose problem elements into their constituent parts, and then actively reorganize them. Sleep does not support the process of decomposition, so it has no significant effect on the resolution of these problems. Several factors have been shown to moderate the effect of sleep on creative problem-solving; these include sleep structure changes, the manipulation of information processing during sleep, and task types. In the existing theoretical mechanisms, complementary learning systems model suggests that memory reorganization is caused by the transfer of information from the hippocampus to the neocortex. Events experienced during wakefulness are initially encoded in the hippocampus, which is a temporary store. During NREM sleep, memories newly encoded into the hippocampus are repeatedly reactivated and thereby become gradually redistributed to the long-term store (i.e., the neocortex). This hippocampal-neocortical dialogue leads to memory consolidation and reorganization. Spreading activation theory suggests that sleep boosts creative problem-solving most likely via spreading activation. Increased spreading activation during REM leads to a larger associative network being activated. This will expand the problem space and highlight novel connections. In addition, synaptic homeostasis hypothesis emphasizes that sleep may benefit memory reorganization by renormalizing synaptic strength to restore cellular homeostasis after net synaptic potentiation during waking. To be specific, synapses in overlapping memories get multiple activations during waking. The stronger the overlap, the more the synapses are activated. When the synapses shrink during sleep, the more activated synapses are likely to be retained, thus preserving overlapping memories and helping to extract the rules of the problem. Recently, some scholars integrated the above theories and proposed the BiOtA model. The model proposes that the iterative alternation between memory replay in REM and NREM boosts the formation of complex knowledge frameworks, and allows these frameworks to be restructured, thus facilitating creative problem-solving. The overlapping memory replay in NREM selectively strengthens shared memories, abstracts the information into the neocortex. In REM, memory representation learned during NREM period are replayed in the neocortex. Such overlapping memory replay in REM will provide a more compressed and thus more abstracted memory representation. Future studies should broaden the scope of research by transforming problem types. Problems frequently encountered in the real world are often much more complex and mainly ill structured. Ill-defined problems may appropriately capture real-world cognitive functioning, therefore they are more worth studying than well-defined problems. Moreover, efforts should be focused on emotional memory and the cross-modal transfer of memories during sleep to deepen the mechanism research. When the problem is difficult to solve, individuals may produce negative emotional memories of the problem, so that the problem-related memories are more strongly activated during sleep, triggering the priority reorganization of them, and thus promoting creative problem-solving. It is necessary to explore the role of emotional memory in the effect of sleep on creative problem-solving. In addition, in the current study, more attention has been paid to the effect of sleep on the reorganization of memory information in single modality. Information gleaned in one modality is potentially useful in other modalities, the cross-modal transfer can further boost creative problem-solving. Therefore, it is necessary to study the effect of sleep on cross-modal transfer to extend the existing mechanism.

Key words: sleep, memory reorganization, creative problem-solving