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Brain reserve
Brain reserve may be defined as the brain's resilience, its ability to cope with increasing damage while still functioning adequately. This passive, threshold model presumes the existence of a fixed cut-off which, once reached, would inevitably herald the emergence of the clinical manifestations of dementia.

Brain size
A 1997 study found that Alzheimer's disease pathology in large brains did not necessarily result in clinical dementia. Another study reported head circumference to be independently associated with a reduced risk of clinical Alzheimer's disease.

While some studies, like those mentioned, find an association, others do not. This is thought to be because head circumference and other approximations are indirect measures.

Number of neuronal connections
The number of synapses is lower in early onset dementia than in late onset dementia. This might indicate a vulnerability to the manifestation of clinical cognitive impairment, although there may be other explanations.

Structures like the cerebellum contribute to brain reserve. The cerebellum contains the majority of neurons in the brain and participates to both cognitive and motor operations.

Genetic component of cognitive reserve
Evidence from a twin study indicates a genetic contribution to cognitive functions. Heritability estimates have been found to be high for general cognitive functions but low for memory itself. Adjusting for the effects of education 79% of executive function can be explained by genetic contribution. A study combining twin and adoption studies found all cognitive functions to be heritable. Speed of processing had the highest heritability in this particular study.