Active processing of declarative knowledge during REM-sleep dreaming

The ability to process recently acquired knowledge is clearly maintained during sleep. Here we assess whether and how far the sleeper controls this processing (in a non-volitional and non-conscious manner). We posit that during sleep, the cognitive concerns of previous waking may guide access to, and processing of, items of declarative knowledge with which those concerns are associated. In a delayed recall task, before each of three sleep onsets in the same night, 12 subjects heard a different nonsense sentence. When awakened in rapid eye movement (REM) sleep, they were asked to report their dream experience and to recall the last sentence heard. Occurrences of incorporation into dream content were more frequent for this sentence than for the sentences heard before previous sleep onsets, and also more frequent than occurrences of similar contents in reports from a control night. However, the modalities of elaboration of dream contents did not vary. These findings indicate that cognitive concern can affect the accessing of recently acquired declarative knowledge during sleep, but not the modalities by which this is inserted into dream content. They also suggest that cognitive concern may help consolidate knowledge by increasing the likelihood of it being processed during sleep.