Brain rhythms are associated with fundamental processes, from sleep to cognitive functions. Targeted approaches that can shape oscillatory activity are needed to understand the mechanisms by which specific rhythms relate to brain function and for clinical interventions. During this talk, I will introduce a Closed-Loop Auditory Stimulation (CLAS) approach to modulate and investigate fast brain rhythms in humans with specificity and selectivity, using targeted auditory stimulation. I will present a series of experiments targeting the alpha oscillation in humans, showing how this approach shapes alpha activity in a phase-dependent manner and can be applied to modulate sleep onset dynamics and REM sleep.