Apparently, since the last regions of the child's brain to mature remain the least myelinated, they're the regions most vulnerable to the insult of Alzheimer's. 'The hippocampus, which processes short- term memories into long-term, is very slow to myelinize. This is why we're unable to form permanent episodic memories before the age of three or four, and why the hippocampus is where the plaques and tangles of Alzheimer's first appear. Hence the ghostly apparition of themiddle-stage patient who continues to be able to walk and feed herself even as she remembers nothing from hour tohour. The inner child isn't inner anymore. Neurologically speaking, we're looking at a one-year-old.