An afternoon nap facilitates analogical transfer in creative problem solving.

In analogical problem solving, the solution to a previously experienced problem (source) is used to solve a new but structurally similar problem (target). Yet, analogical transfer is seldom successful, as structural commonalities between source and target problems can be difficult to recognise. Theoretically, memory consolidation processes during REM sleep may help to identify and strengthen connections between weakly related memories, improving the ability to use analogical transfer. In the current experiment, participants attempted to solve source problems, were told the solutions, and then attempted to solve new but structurally similar target problems. After a 2-h break including a nap (n = 28) or wakefulness (n = 30), participants attempted to solve target problems they were unable to solve before the break. Measures of source problem memory and perceived similarity between source and target problems were also obtained. The nap group solved a greater proportion of target problems after the break than the wake group, despite no group differences in solution rates before the break or source problem memory. The nap group also perceived greater similarity between source and target problems after the break than the wake group, and the time spent in REM sleep predicted the proportion of post-break target problems solved. These results indicate that sleep improves the ability to solve target problems that could not be initially solved and suggest that REM sleep improves the use of analogical transfer by highlighting commonalities between source and target problems that were unnoticed before a nap.