Distinct rates of cognitive decline associated with normal aging

Abstract

The subtle interface between normal and pathological aging has been a field of intense research lately. While much emphasis has been put on the characterization of mild cognitive impairment and patterns of cognitive decline within various dementing disorders, classic signature and biological underpinnings of cognitive changes associated with normal aging are still poorly understood. This holds great importance in deciphering the secret of successful aging and better distinguishing normal from diseased states. We sought to evaluate the decline in memory, visuospatial, executive and language functions associated with normal aging. As part of the validation of the ‘Dépistage Cognitif de Québec’ (DCQ), a novel cognitive screening test for atypical/complex dementias, 180 normal individuals from 51 to 88 years-old (mean 67) were tested. The DCQ is made of 5 distinct sections, namely Memory, Visuospatial, Executive, Language and Behaviour. We cross-sectionally analyzed the scores within these domains as a function of age and generated ‘cognitive curves’ to estimate which domain shows the most significant age-related decline. Among the five indices, executive functions were the most affected by aging (-0.71%/year), followed by memory (-0.44%/year) and visuospatial skills (0.33%). Language abilities were globally preserved in the different age groups (-0.26%/year). Within the executive domain the Stroop Color-Word Test (-2.1%/year) was the most affected by aging followed by Verbal fluency (-1.2%/year). Of note, 82% of the 70- individuals succeeded at the Stroop (naming correctly ≥ 14 colors in 15 seconds), compared to only 42% of 70+ individuals.