Clues for a theoretical sleep-related forgetting

The idea that sleep improves memory processing has a long history and has been highly challenged and enriched these last decades. While Crick & Mitchison [1] early suggested that sleep could promote forgetting of daily unwanted memories, their hypothesis failed to reach researchers mind as most of the investigations reported opposite results, that is, sleep prevented forgetting. Now a wide range of evidence supports the sleep-related memory consolidation theory and coherent models considering the structural complexity of both memory and sleep begin to emerge [2,3]•. Although current theory may acknowledge that passively forgetting some information would be a consequence of overnight consolidation of others memories [3], one might deplore that the relationship between sleep and forgetting has not been further investigated. Fortunately, the cognitive processes underlying forgetting are more and more understood [4]•, but it seems that research on forgetting and the one on sleep and memory do not benefit from each other yet. This short note aims to review evidence for such a connection and to examine whether sleep could be related to an active forgetting process and also be compatible with the current sleep-related memory consolidation theory. Therefore, we will first analyze a part of the large amount of data on sleep, memory (especially the hippocampal-dependent declarative memory) and forgetting. We will then suggest a model, according to which sleep may promote a forgetting mechanism based on the selective retrieval of some memories over others. Finally, we will challenge this model with original studies published these past two years that tackled with the issue of sleep and forgetting.