Anticipated reward enhances offline learning during sleep.

Sleep is known to promote the consolidation of motor memories. In everyday life, typically more than 1 isolated motor skill is acquired at a time, and this possibly gives rise to interference during consolidation. Here, it is shown that reward expectancy determines the amount of sleep-dependent memory consolidation. Subjects were trained on 2 different sequences of a finger sequence motor task before 12-hr retention intervals of either nocturnal sleep or daytime wakefulness. After training was finished, reward expectancy was varied by announcing a monetary reward for performance improvement at retesting on either the first- or second-trained sequence. Before the retest, however, subjects were informed that reward would depend not on only 1 sequence but on the average performance for both sequences. Posttraining sleep enhanced overall finger sequence performance. The sleep-dependent gain in skill was significantly greater for the sequence that was associated with monetary reward after training, regardless of whether this sequence was the first or second to be trained. After wake retention intervals, no or only minor performance gains were observed. The data show that expectancy for a reward enhances offline learning of a skill during sleep.