I am curious, could you tell me what part of the brain you are talking about? I would assume that the frontal lobes would be where 'logic' would be, as it is the center of higher mental cognition and reasoning. But I know that the frontal lobes are not shut down durning sleep so you must be refering to some other part of the brain. I am also confused because when we are in REM sleep, where most vivid dreams occur, the human EEG looks identical to that of a fully awake and mentally aware person. Granted, certain neurotransmitters cease being produced (seretonin and NE) and other wash over the brain (acetylcholine) which is always what I have understood is used to explain the bizarreness of dreams and our inability to remember them well. This is all physiological, though and while I have studied the physiology of dreams and sleep extensively, I don't feel that lucidity is at all explained by any of it.