A recent Harvard experiment (Payne et. al., 2009) shows that an afternoon nap selectively increases false recall of semantically similar critical words to presented words [see DRM paradigm]. This is because sleep plays an active rather than a merely passive role in memory consolidation. Upon waking, experimenters found that subjects remember the gist of the presented items more easily than specific words, which probably accounts for this effect.
This result may be because the DRM paradigm engages semantic memory more then episodic memory. Where as semantic memory extracts semantic regularities to emphasize what memories share in common, episodic memory stores veridical details to keep memories separate.
Sleep does more than simply consolidate memories in veridical form, additionally transforming and restructuring them so that insights and abstractions can be made, inferences can be drawn, integration can occur, and emotionally salient aspects of information can be preferentially remembered over neutral aspects. (Payne et. al., p.333, in-text references removed)
Sleep transitions the experience of particulars into generalities, universals and abstractions. When I read of this quality of sleep, I thought of Aristotle's posterior analytics (post. an.) and it's high esteem for demonstration. I think I should read it again with thoughts of memory and the nature of the mind to create representations of the world around it. On first blush it seems the will is not needed to forge rational demonstrations. Like bayesian reasoning, even the unconscious and undirected parts of our minds can process information in sophisticated and defensible ways.
Payne, J.D., Schacter, D.L, Propper, R.E., et. al. (2009) The role of sleep in false memory formation. Neurobiology of Learning and Memory. 92. 327-334
Roediger, H.L., III, McDermott, K. B. (1995). Creating false memories: Remembering words not presented in lists. Journal of Experimental Psychology: Learning, Memory, and Cognition, Vol. 21, 803-814.