Sleep after learning enhances flexibility of memory retrieval in 12-month-old infants
In the present study, we examined the effect of sleep on the flexibility of declarative memory retrieval using a deferred imitation paradigm (Barr et al., 1996; Hayne et al., 1997). Forty-one 12-month-old infants were randomly assigned to a nap condition, a no-nap condition, or a baseline control condition. In a demonstration session, infants in the nap and no-nap condition watched an experimenter perform three target actions on a hand puppet. To enhance encoding opportunities, infants were allowed to practice the target actions three times immediately afterwards (Hayne et al., 2003). Flexibility of memory retrieval was assessed in a test session 4-hr later with a puppet that was identical in shape but different in color from the one used during the demonstrations. Infants in the nap condition were scheduled to sleep (>30 min) during the 4-hr interval while infants in the no-nap condition were naturally scheduled to stay awake. Sleeping behavior was monitored using actigraphy. Infants in the baseline-control condition only saw the stimuli during the test session to assess spontaneous production of the target actions. The results indicate that only infants in the nap condition performed a significantly higher number of target actions at test than infants in the baseline-control condition, t(20.99)=-2.202, p=.039. Our results point towards a facilitative effect of sleep on the flexibility of memory retrieval in 12-month-old infants. This indicates that sleep dependent memory consolidation can change the quality of memory traces already in infants.