Apathy in Older Adults is Associated with a Selective Over-Weighting of Effort in Everyday Decisions

Apathy, characterized by diminished motivation and reduced goal-directed behavior, is prevalent in normal aging. Recent evidence suggests that it may result from biases in the evaluation of costs and benefits during decision making. However, most research has focused on simple decisions involving the trade-off between motor or cognitive effort and monetary reward. Meanwhile, it is possible that the disrupted real-life decisions of people with apathy reflect biases affecting many other dimensions of value. Additionally, the extent to which mood symptoms that frequently co-occur with apathy also contribute to biases in decision making is unclear. To address these gaps, we developed a novel online task completed by 158 older adults who first rated everyday activities (e.g., watching TV, going to the park) across 19 value attributes (e.g., enjoyment, social obligation), and then made a series of choices between random pairs of the different activities. A factor analysis of attribute ratings identified three latent factors representing reward, effort, and obligation, which strongly predicted choices and choice response times. Apathy was selectively associated with an overweighting of effort-related attributes in models controlling for impulsivity, depression, or anhedonia; it did not affect the weighting of reward or obligation-related attributes. Interestingly, impulsivity, which was positively correlated with apathy, was associated with an underweighting of effort. Hierarchical drift diffusion modelling supported these findings, showing that apathy and impulsivity modulated the influence of effort on the rate of evidence accumulation in opposite directions. Overall, these results suggest that decisions about everyday activities rely on the integration of a wide range of value attributes and that apathy is selectively associated with an overweighting of the effort dimension of value, driving choices away from activities that require greater effort.