Sleep and Memory: Behavioral and molecular consequences of sleep deprivation

Sleep loss is a serious problem in our society. The major aim of this thesis was to investigate the effects of sleep deprivation on the different stages involved in memory processing and to assess the underlying mechanisms in the brain. The findings of this thesis show that acute, relatively short sleep deprivation can have a negative effect on the encoding, consolidation and adaptation of a memory and on the behavioural performance in a learning task. Importantly, the disruption of memory processes by sleep deprivation is not mediated by waking interference by sensory stimulation or stress hormones during waking, but actually seems to be related to the amount of lost sleep. Especially memory for learning tasks that are dependent on the hippocampus, an important brain area involved in memory processing, is sensitive to sleep deprivation. Deprivation of sleep following learning induces in the hippocampus a reduction in the expression of activated CREB, a protein that is critically involved in memory formation. The most important finding is that the effect of sleep deprivation may not always be directly evident on the level of behavioral performance, since the brain, when possible, can temporarily compensate for the negative effects by promoting the use of alternative learning mechanisms and brain areas involved that seem to be less sensitive to sleep deprivation. However, the effects of sleep deprivation can still appear later, long after the actual sleep loss, because the use of alternative learning mechanisms can result in reduced flexibility under changing conditions that require adaptation of the previously formed memory.