Heterogeneity of effects of cognitive reserve on performance in probable Alzheimer's disease and in subjective cognitive decline

Objective: Cognitive reserve (CR) is a term used to describe the adaptability of cognitive processes to brain changes. It helps to explain the different cognitive adaptation to daily functioning in aging individuals and in individuals with brain pathology: a higher CR is associated with a delay in the manifestation of cognitive symptoms. CR is estimated using different proxies, such as education, cognitively stimulating life experiences, premorbid intelligence quotient (IQ), and vocabulary size. Despite the complexity of CR, little research to date has systematically focused on the heterogeneity of its effects. Method: We investigated this issue in individuals with probable Alzheimer's Disease (AD) and in individuals with subjective cognitive decline (SCD) by focusing on two variables: (a) the type of CR proxy (i.e., Education and Life experience) and (b) the type of test used to assess cognitive performance (i.e., theMini-Mental State Examination [MMSE] screening test and the extensive Brief Neuropsychological Examination-2 [ENB-2] test battery). Results: Our results suggest that effects on CR varied: in individuals with probable AD, we found a positive relationship of Education with performance on both the MMSE and the ENB-2 tests; in contrast, individuals with SCD showed a positive relationship of a Life experience proxy selectively with the ENB-2 global score. Conclusions: Different proxies may reflect different compensatorymechanisms of CR depending on task demand and on an individual's global cognitive condition. In particular, while the Education proxy can capture CR-related cognitive compensation in a pathological condition such as probable AD, the more complex Life experience proxy might be useful for capturing CR-related effects when signs of deterioration are subtle, like in SCD.