The aim of this project is to look at changes in dendritic calcium activity during sleep and how these changes are influenced by waking experience in freely behaving animals. Sleep promotes brain plasticity and processes dependent upon plasticity (i.e. memory consolidation). But the cellular events that mediate these effects are poorly understood. We hypothesize that sleep promotes brain plasticity by increasing synaptic activity locally. We will test this hypothesis by looking at changes in in vivo dendritic calcium transients during sleep (Aim1) and sleep-dependent cortical plasticity (Aim2) in freely behaving animals. This will be achieved by combining EEG/EMG polysomnography recording and fiberoptic imaging techniques. More specifically, we will look at changes in calcium activity from the apical tuft dendrite of layer 5 pyramidal neurons. Dendrites are the main site of information processing and integration therefore changes observe over the sleep-wake cycle will contribute to a better understanding of synaptic function in the intact brain (Aim1). Changes in dendritic calcium levels are also directly linked to neuronal activity and can predict the polarity of plastic changes (e.g. synaptic potentiation vs. depression). Therefore, we expect that challenging the brain during wakefulness will modify dendritic activity during subsequent sleep. To test this hypothesis, we will quantify dendritic calcium activity during sleep following 2 different experience-dependent plasticity paradigms leading to either potentiation (enriched environment) or depression (monocular deprivation) in primary visual cortex (Aim2). The proposed research would be the first to assess directly the effect of sleep, experience-dependent plasticity and sleep-dependent plasticity on in vivo dendritic calcium activity in freely behaving animal.