Sleep and Its Effects on Synaptic Strength

Throughout the history of sleep research, many theories have been put forward in an attempt to explain the function of the state of sleep. The most popular and well-accepted theory among sleep researchers today is that sleep plays an important role in learning and memory by affecting mechanisms of synaptic plasticity. At the present time, there are two main competing views regarding how sleep affects memory – the active system consolidation model and the synaptic homeostasis hypothesis (SHY). The former proposes that sleep is a time for the reactivation and redistribution of memory traces, while the latter emphasizes the role of sleep in improving signal-to-noise ratios and learning by down-regulating synaptic strength. In recent years, SHY has been widely discussed by sleep researchers. It has also been criticized for, for example, being too vague, ignoring contradictory evidence and misrepresenting available evidence. The aim of this review is to critically analyze SHY by considering recently published empirical evidence as well as criticism raised against the theory. The conclusion drawn from the analysis is that although SHY seemingly hold up well against recent contradictory empirical evidence, it faces serious problems with the criticism raised against it.