Apathy and everyday decision-making in Parkinson’s disease and normal aging

Apathy is a neuropsychiatric syndrome characterized by diminished motivation and reduced initiation of goal-directed behavior (Marin, 1990). Apathy is highly prevalent in neurological (e.g., Parkinson’s disease, frontotemporal dementia) and psychiatric (e.g., schizophrenia) conditions, and is also observed in otherwise healthy individuals, particularly in the elderly (Clarke et al., 2010; Bortolon et al., 2018; den Brok et al., 2015). Neurocomputational theories suggest that decision-making reflects the integration of multiple value dimensions, including anticipated rewards and effort costs. Within this framework, apathy has been hypothesized to reflect an altered integration of value dimensions (e.g., Bonnelle et al., 2015). Specifically, apathetic individuals may overweight costs during value-based decision-making (e.g., Kim et al., 2025), leading individuals to disengage from potentially valuable activities. Empirical support for this account largely derives from experimental paradigms examining simplified trade-offs between motor effort and monetary reward. Two critical gaps remain. First, typical experimental paradigms capture only a narrowed subset of value dimensions relevant to real-world decision-making. Everyday activities potentially affected by apathy involve multiple dimensions of value beyond motor effort and monetary reward, such as cognitive costs, social expectations, planning demands, and other contextual dimensions. It remains unclear how these diverse value dimensions are integrated during decision-making, and whether apathy selectively alters the integration of specific value dimensions. Moreover, existing paradigms typically do not distinguish potentially distinct processes underlying apathy, such as altered subjective valuation (e.g., perceiving activities as more effortful) and altered weighting of value dimensions during choice (e.g., effort exerting a stronger influence on choice). Disentangling these processes is essential for clarifying the mechanisms underlying apathy. Second, it is widely assumed that measures derived from decision-making tasks (e.g., sensitivity to effort and reward) reflect stable motivational traits. Yet, this assumption remains largely untested. For example, it is expected that an individual displaying high effort avoidance in an experimental task will engage less frequency in self-engaged effortful everyday activities compared to an individual with lower effort avoidance. Demonstrating correspondence between experimental measures of value sensitivity and real-world activity engagement would strengthen the ecological relevance of decision-making paradigms used to study apathy. The present study aims to address these gaps using an ecologically grounded decision-making paradigm in which older adults with and without Parkinson's disease rated everyday activities across multiple value attributes designed to be related to effort (e.g., physical effort, cognitive effort, difficulty of initiation), reward (e.g., enjoyment of the activity, anticipated outcome, social engagement), and obligation (e.g., self obligation, social obligation), along with additional contextual attributes (e.g., frequency, time cost, health interference). Participants subsequently chose between pairs of activities. This design allows us to characterize how different value dimensions influence decisions between everyday activities. It also allows us to dissociate subjective valuation (how activities are rated) from value weighting during choice (how activity ratings affect decisions). We will examine how apathy symptom severity influences these processes using both behavioral models of choice and computational modeling using drift diffusion models. We will also examine whether apathy is associated with a bias toward choosing more passive over more active everyday activities, reflecting a manifestation of reduced goal-directed engagement. Finally, we will examine whether value sensitivity derived from the task can be generalized to self-reported engagement in everyday activities, providing an initial assessment of the real-world relevance of the paradigm.