Cognitive reserve

A distinction is drawn between "brain reserve" (passive, structural — the number of neurons, volume, synapses) and cognitive reserve (active, functional — how the brain uses its resources). The latter explains why, at an equal degree of damage, the clinical manifestations differ so much: a brain with high reserve "takes the hit" longer.

Reserve is built throughout life: education, intellectually demanding work, learning, reading, games, and social and physical activity are associated with a slower decline in cognition and a lower risk of dementia. This rests in part on neuroplasticity — the brain's ability to rewire its connections in response to experience.

A key fact: people with high reserve tolerate more Alzheimer's disease pathology without symptoms (shown by the work of Katzman and the "Nun Study"). But reserve does not protect against the disease itself — it only delays its manifestations. Once compensation is exhausted, decline can proceed faster. Building reserve is beneficial at any age.