NREM sleep memory

Incongruities such as the dream character who has the physical attributes of one person that we know and the face of another illustrate an indiscriminate but perhaps functionally significant over-inclusiveness in the categories of unconscious memory systems. We can get at this process by using semantic memory tests of subjects awakened from REM and tested both immediately and later when the sleep inertia is over. Compared to waking and to NREM sleep, we find the expected REM enhancement of weak primes (i.e., loose associations) but, to our surprise, not of strong primes (strong associations). 

The basic hypothesis, for which evidence was previously consistent and positive but not impressively robust, is that rapid eye movement (REM) sleep subserves consolidation of memory. This hypothesis is appealing because the brain is activated and dreams are composed of memory fragments. This hypothesis has been borne out by recent experiments, although it now appears that non-REM (NREM) sleep is equally important. More interestingly, the dream-memory plot has thickened in two important ways ... 

---