Phase 1 · Understand the Body — Why the disease behaves the way it does.
The One-Line Truth
The whole disease in one chain
Everything on this page exists to explain this line.
In neurocognitive disorders, the team that spots early memory loss, asks one good screen question, and checks for reversible causes outperforms the team that assumes it's just old age.
A Library Losing Its Librarians and Shelves
Your brain is like a library: books are memories, the hippocampus is the librarian who tags and files each new book, shelves are the cortex where facts live, and chemical messengers (acetylcholine, dopamine) are the lighting system that makes reading possible. In neurocognitive disorders, plaques and tangles are like water damage that kills the librarian and rots the shelves—new books (memories) can no longer be filed because the librarian is gone, old books become impossible to find because their shelf markers are erased, and the lights flicker (acetylcholine drops) so even if a book is there, no one can read it. As more shelves warp and the librarian's desk crumbles, you can no longer navigate the library at all—you lose the directory (visuospatial), forget why you came (executive function), and cannot ask for help (language breaks). Eventually the whole building is condemned: only the basement (brainstem) keeps the lights on and the doors locked, but no one can live there anymore.
American Academy of Neurology (AAN) practice guideline on mild cognitive impairment and dementia · Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5-TR) · Alzheimer's Association clinical criteria · UpToDate: Evaluation of cognitive impairment and dementia · reviewed 2026-07-07