Most adults fear the onset of dementia in general, and Alzheimer's disease in particular, more than physical disability. Many ask: What is Alzheimer's disease? Could I have it? Clear answers about Alzheimer's dementia and what is required to live a long, mentally healthy life requires first an understanding of how the brain's many types of cells connect, share and disengage. Recent studies show unequivocally that the n-neuron cells of the brain, the glia and microglia, actively participate in maintaining its well-being. Yet, glia and microglia are also significant participants in the demise of the memory neurons lost in Alzheimer's dementia. Inside the Closed World of the Brain is organized to take a reader on a journey through the brain that begins with tactics for quickly learning the necessary words. Next, there is an explanation of the general organization of the human brain both at the visual and microscopic level. After that the brain's system for internal quality control of its watery environment, critical for neuron function, is described. From there the reader is introduced to all of the cells of the brain and how they work together under rmal circumstances to form memory and acquire language. Then, what science w kws about how this system fails in Alzheimer's dementia is presented. Postmortem data from long-lived, mentally competent people is compared to that from people who died of Alzheimer's disease. This comparison, only recently available, is leading to a re-evaluation of how Alzheimer's disease develops and provides clues for development of new therapies.