Dementia
A progressive, acquired decline in cognitive function severe enough to impair daily function, whose pattern of deficits directly reflects which brain networks the underlying pathology, most often amyloid and tau, Lewy bodies, or vascular injury, has damaged.
First principles
Dementia is a syndrome, not one disease: the pattern of loss reveals which network is failing
Cognition depends on distinct but interacting networks: medial temporal and hippocampal circuits for new memory formation, frontal circuits for executive function and behaviour, parietal circuits for visuospatial processing, and subcortical circuits for processing speed and attention. Different underlying pathologies target different networks first, so the earliest and most prominent symptoms predict the underlying cause. This is why dementia is a syndrome with several distinct causes rather than a single disease, and why the pattern of deficits, not just their presence, is diagnostically useful.
Educational content pending clinical review. Not medical advice.