Insights into sleep's role for insight: Studies with the number reduction task

In recent years, vibrant research has developed on “consolidation” during sleep:To what extent are newly experienced impressions reprocessed or evenrestructured during sleep? We used the number reduction task (NRT) to study ifand how sleep does not only reiterate new experiences but may even lead to newinsights. In the NRT, covert regularities may speed responses. This implicitacquisition of regularities may become explicitly conscious at some point,leading to a qualitative change in behavior which reflects this insight. Byapplying the NRT at two consecutive sessions separated by an interval, weinvestigated the role of sleep in this interval for attaining insight at thesecond session. In the first study, a night of sleep was shown to triple thenumber of participants attaining insight above the base rate of about 20%. Inthe second study, this hard core of 20% discoverers differed from otherparticipants in their task-related EEG potentials from the very beginningalready. In the third study, the additional role of sleep was specified as aneffect of the deep-sleep phase of slow-wave sleep on participants who hadimplicitly acquired the covert regularity before sleep. It was in theseparticipants that a specific increase of EEG during slow-wave sleep in the 10-12Hz band was obtained. These results support the view that neuronal memoryreprocessing during slow-wave sleep restructures task-related representations inthe brain, and that such restructuring promotes the gain of explicitknowledge.