Exploring strategies to operationalize cognitive reserve: A systematic review of reviews.
BACKGROUND
The cognitive reserve hypothesis suggests that across the lifespan, higher education, regular participation in social or mentally stimulating activities, and complexity of occupation increase an individual's resistance to dementia. However, there is currently no consensus regarding how to assess or measure cognitive reserve.


METHODS
We performed a systematic review of reviews focused on the concept of cognitive reserve to examine key elements of the definition and highlight limitations. We searched Embase.com, MEDLINE (OvidSP), the Cochrane Library, Web of Science, Scopus, Google Scholar, and PubMed.


RESULTS
Five systematic reviews were identified. These incorporated findings from cohort, cross-sectional, and case-control studies, and the outcomes examined included Alzheimer's disease, vascular dementia, nonspecified dementia, all dementias, and cognitive decline or cognitive impairment. Education, occupation, and leisure or mentally stimulating activities were suggested to supply cognitive reserve and offer a protective effect against the risk of dementia. Premorbid IQ and socioeconomic status have not been investigated as thoroughly and showed inconsistent results. Two of the reviews showed that when combining different indicators in the analyses/definition, including education, occupation, mentally stimulating activities, and premorbid IQ, cognitive reserve had a protective effect against cognitive decline. However, other indicators may also supply the reserve, including dietary habits and genetic indicators, but research is lacking with regard to creating a full cognitive reserve model.


CONCLUSIONS
This review highlights the lack of consensus regarding a definition of cognitive reserve. Further research is required to clarify how the indicators already identified may provide cognitive reserve and offer a protective effect against dementia. Agreement on the indicators that constitute the cognitive reserve model is needed before testing possible interventions that may increase the reserve supply and improve cognition.
a Institute for Health and Society, Newcastle University , Newcastle , UK.
Stephanie L
SL
Harrison
Ayesha
A
Sajjad
Wichor M
WM
Bramer
M Arfan
MA
Ikram
Henning
H
Tiemeier
Blossom C M
BC
Stephan
D000375:Aging / Q000523:psychology*; D003071:Cognition / Q000502:physiology*; D058245:Cognitive Reserve / Q000502:physiology*; D003704:Dementia / Q000523:psychology*; D018450:Disease Progression; D006801:Humans; D009483:Neuropsychological Tests
Alzheimer’s disease; Brain reserve; Cognitive reserve; Dementia; Education