Given that children and adolescents undergo entirely different maturational processes (children show an increase, adolescents a decrease in synapse density) larger diurnal changes in children are expected compared to adolescents concerning brain metabolites and structural markers. These cortical changes in synapse density are thought to be reflected in electrophysiological markers in the sleep EEG (children show a higher slow wave activity, adolescents a reduced slow wave activity). With the modulation of the deep (slow wave) sleep by playing short, low volume tones, the investigators want to test if there is a causal relationship between slow wave sleep and markers of cortical plasticity.