Cognitive reserve is the brain's resilience against pathology. The difference between brain damage seen on imaging and the clinical symptoms expressed.
Mechanism: Built through education, intellectually demanding work, multilingualism, social complexity, and novel skill acquisition across the lifespan. High-reserve brains can sustain significant Alzheimer's pathology without dementia.
Use case: Keep learning hard things. Maintain social complexity. Engage in cognitively demanding work as long as possible. Read difficult books, learn languages, take on new domains.
Caveats: Reserve doesn't prevent pathology. It delays symptoms. Maintain it AND minimize risk factors.