A new study from the University of Southern California adds a structural dimension to one of medicine's long-standing puzzles: why depression so often precedes dementia. Researchers examining brain scans from over two thousand older adults found that those with depression showed measurable shrinkage in a specific hippocampal region called CA23DG — a composite area central to memory, learning, and spatial navigation. Notably, this reduction held even after accounting for the biological signatures of Alzheimer's disease, suggesting depression may carve its own separate path through the brain's m