Increased cognitive effort costs in healthy aging and preclinical Alzheimer disease

Life-long engagement in cognitively demanding activities may mitigate against declines in cognitive ability observed in healthy or pathological aging. However, the “mental costs” associated with completing cognitive tasks also increases with age and may be partly attributed to increases in preclinical levels of Alzheimer disease (AD) pathology. We test whether cognitive costs increase in a domain-general fashion in older adults, and further, whether such age-related increases in cognitive effort cost are associated with amyloid burden, a signature pathology of AD. In two experiments, we administered an objective measure of cognitive effort (Cognitive Effort Discounting: COG-ED) to a sample of older adults recruited from online sources (Experiment 1) or from ongoing longitudinal studies of aging and dementia (Experiment 2). Experiment 1 compared age-related differences in cognitive effort across two distinct domains, working memory and speech comprehension. Experiment 2 compared cognitive costs between a group of participants who were rated positive for amyloid burden relative to those who had no evidence of amyloid. Results showed age-related increases in cognitive effort cost were evident in both domains. Cost estimates were highly correlated between the working memory and speech comprehension tasks and were present even when controlling for overall working memory capacity. In addition, older adults who were amyloid positive had higher cognitive cost estimates than those who were amyloid negative. Cognitive effort costs may index a domain-general trait that consistently increases in healthy aging. Differences in amyloid burden suggest a potential neurobiological mechanism for age-related increases in cost.