Role of Sleep in Formation of Relational Associative Memory

Relational memory, the ability to make and remember associations between objects, is an essential component of mammalianreasoning. In relational memory tasks, it has been shown that periods of offline processing, such as sleep, are critical to mak-ing indirect associations. To understand biophysical mechanisms behind the role of sleep in improving relational memory,we developed a model of the thalamocortical network to test how slow-wave sleep affects performance on an unordered rela-tional memory task. First, the model was trained in the awake state on a paired associate inference task, in which the modellearned to recall direct associations. After a period of subsequent slow-wave sleep, the model developed the ability to recallindirect associations. We found that replay, during sleep, of memory patterns learned in awake increased synaptic connectiv-ity between neurons representing the item that was overlapping between tasks and neurons representing the unlinked itemsof the different tasks; this forms an attractor that enables indirect memory recall. Our study predicts that overlapping itemsbetween indirectly associated tasks are essential for relational memory, and sleep can reactivate pathways to and from over-lapping items to the unlinked objects to strengthen these pathways and form new relational memories.