Summary While the benefit of sleep after learning in offline consolidation is established , a role for sleep before learning in promoting initial memory formation remains largely uncharacterized. Existing theoretical frameworks speculate that accrued time awake, associated with ongoing experience, decreases learning capacity, while specific non-rapid-eye-movement (NREM) oscillations support restoration of learning ability [1,2]. Despite these model predictions, it remains untested whether episodic learning capacity remains stable across the day, or is progressively compromised by continued time awake. Furthermore, it is similarly unclear whether the presence, rather than the detrimental absence, of sleep restores efficient learning ability, and if so, what aspect(s) of sleep physiology support such reinstatement [3,4]. We have tested these related hypotheses, and report here a learning interaction, such that episodic encoding capacity deteriorates across a daytime waking interval, but sleep and associated NREM spindle oscillations restore efficient learning ability.