Cognitive reserve is the theory that lifelong mental stimulation builds resilience against brain damage and neurodegeneration. Individuals with higher cognitive reserve — typically indexed by education, occupational complexity, and engagement in intellectually stimulating activities — can tolerate more brain pathology (such as Alzheimer's plaques and tangles) before showing clinical symptoms. The concept explains why two people with similar brain pathology can show very different levels of cognitive functioning.
Evidence
Epidemiological studies consistently show that higher education and occupational complexity are associated with lower risk of dementia diagnosis, even when postmortem neuropathology is equivalent. The Nun Study found that linguistic complexity in early life essays predicted dementia risk decades later, and that some individuals with extensive Alzheimer's pathology had shown no symptoms during life.
Brain reserve refers to physical structural differences (more neurons, more synapses) that provide a buffer against pathology. Cognitive reserve refers to the efficiency and flexibility of cognitive processes — the ability to use existing brain networks more efficiently or to recruit alternative networks when primary networks are damaged. Both contribute to resilience, but cognitive reserve emphasizes the importance of lifelong cognitive engagement in building and maintaining neural resources.