In sum, the theory postulates a crucial role of slow oscillatory activity in synchronizing hippocampal memory reactivations with thalamo-cortical spindle activity, thereby redistributing and integrating the memories into neocortical long-term stores. How can we empirically test the theoretical assumption of a critical role of memory reactivations during sleep for processes of memory consolidation? If reactivation during sleep indeed plays a functional role for the consolidation of memories, experimentally increasing these reactivations should have beneficial consequences for consolidation processes during sleep and result in improved memory performance the next day. Before we will present evidence for the beneficial effect of TMR by reexposure to memory cues during sleep, we will briefly discuss the capability of the sleeping brain to processes sensory stimuli and discriminate semantic categories.