The ability to compensate for brain changes associated with dementia by the use of functional brain processes has been alluded to as cognitive reserve. First introduced by Neuropsychologist Yaakov Stern in the early 2000s, this heuristic construct is based on the observation that people with similar pathological burden showed differences in their cognitive functioning. As compared to brain reserve (the neuronal “capital” of a person), cognitive reserve is thought of as malleable by experience. In particular, factors such as education, occupation or leisure activity engagement have been proposed as “proxies” (i.e. correlates) of cognitive reserve. Stress has emerged as a potential modifiable risk factor for cognitive decline and dementia. In particular, both psychological and physiological measures of stress have been associated with faster dementia progression and a higher risk for Alzheimer's disease.
The link between stress and cognitive reserve in relation to cognition, however, is unclear. In a recent study published in the journal Alzheimer’s and Dementia, a group of researchers based at the Karolinska Institutet in Stockholm (Sweden) has examined whether a composite measure of cognitive reserve is associated with cognitive functioning, and whether subjective and objective measures of stress explain these associations. In particular, 113 participants of the Cortisol and Stress in Alzheimer's disease cohort study (Co-STAR) rated subjective stress levels and provided measures of saliva cortisol (thought of as reflective of physiological stress). Information about education, occupation, level of social contact and leisure activity engagement was used to derive a composite measure of cognitive reserve, the cognitive reserve index (CRI). Performance on neuropsychological tests of memory, processing speed, working memory and perceptual reasoning was assessed at baseline and throughout three years of follow-up. Furthermore, samples of cerebrospinal fluid were collected to assess levels of Alzheimer's disease biomarkers.
The authors found that higher CRI scores were associated with better cognition at baseline and follow-up. Controlling for salivary cortisol (but not the subjective stress measure) attenuated observed associations. CRI scores were not associated with AD biomarker levels. These findings suggest that stress may weaken the protective benefits of cognitive reserve and highlight the importance of stress reduction practices for promoting good cognitive functioning. https://alz-journals.onlinelibrary.wiley.com/doi/10.1002/alz.13866