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Text page Brain Reserve The term brain reserve reflects structural properties of the brain such as brain volume (Bigler et al., 2006), cerebral metabolism (Cohen et al, 1999), lesion loads (Cader et al., 2006) and patterns of  structural connectivity (Alstott et al., 2009; Becker et al., 2016).

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.

(Depending on their amount of 'reserve', different people show different abilities to compensate for, or cope with, brain pathology. 'Brain reserve' refers to the structural elements that mediate one's resilience to pathology/injury-già detto altrove). Thus, the Brain Reserve hypothesis (should we leave this expression like this? Everyone seem to use it, but in this page we use 'hypothesis' here for the first time) is a passive-quantitative model which ascribes different level of resilience to variables such as brain volume and synapse count. The The Cognitive Reserve hypothesis, instead, suggests that the brain actively attempts to cope with damage by optimizing its remaining resources: it can use pre-existing cognitive processes or enlist compensatory strategies. Cognitive reserve involves the ability to recruit networks, so a high CR entails more efficient plasticity. In this sense, CR represents the active side of one's 'reserve' and describes the resilience of the mind (functional), as opposed to that of the brain (structural). However, brain plasticity has been proposed as a mechanism (Fratiglioni, 2007) that may contribute to both brain and cognitive resilience. In fact, BR and CR can not be considered as distinct and independent. Cognitive strategies need to be implemented at a neural level (ref 2) in terms of efficiency, capacity and flexibility of synaptic reorganization, as well as relative use of specific brain regions. Similarly, intensive cognitive stimulation may be associated with increased brain volume in childhood (e.g., 8) So far, references are contained in: Cognitive Reserve Index questionnaire (CRIq): a new instrument for measuring cognitive reserve Aging Clinical and Experimental Research Massimo Nucci1, Daniela Mapelli1,2 and Sara Mondini1 -education as a mediator .Notably, education is associated with brain reserve and people with higher education can cope with brain damage for a longer time. Functional imaging studies report that higher education is associated with more severe pathology in patients with Alzheimer's disease, controlling for disease severity. Therefore, schooling seems to provide brain reserve against neurodegeneration.( Schooling mediates brain reserve in Alzheimer's disease: Findings of fluoro-deoxy-glucose-positron emission tomography  October 2006     Journal of neurology, neurosurgery, and psychiatry 77(9):1060-3      DOI: 10.1136/jnnp.2006.094714) On the one hand, education is bound to increase CR through the development of a variety of cognitive strategies (Manly, Byrd, Touradji, Sanchez, & Stern, 2004; Stern, 2002); on the other hand (from the structural viewpoint) it also promotes synaptic growth (Katzman, 1993), i.e. it increases brain reserve

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.