Altered reward processing underpins emotional apathy in dementia

Introduction: While apathy is broadly defined as a loss of motivation, it is increasingly recognised as a multidimensional syndrome spanning executive, emotional, and initiation domains. Emotional apathy is purportedly driven by deficits in using socioemotional rewards to guide behaviour, yet the link between these symptoms and reward processing, and their common neural correlates, has not been directly examined. 

Methods: Sixty-four patients (33 behavioural-variant frontotemporal dementia, 14 Alzheimer’s disease, 8 semantic dementia, 6 progressive nonfluent aphasia, 3 logopenic progressive aphasia) were classified into high (HEA; n = 36) and low (LEA; n = 28) emotional apathy groups based on emotional apathy subscale scores on the Dimensional Apathy Scale. Patients and age-matched healthy controls (n = 27) performed an instrumental reward learning task where they learned to associate cues with either social or monetary outcomes. 

Results: HEA patients showed impaired learning on both the social and monetary reward conditions, relative to LEA patients (p = 0.016) and controls (p = 0.005). Conversely, the LEA group did not differ from controls (p = 0.925). Importantly, multiple regression analyses indicated that social reward learning significantly predicted emotional apathy. Voxel-based morphometry analyses revealed that emotional apathy and social reward learning were both associated with orbitofrontal cortex, ventral striatum, and insula atrophy. 

Discussion: Our results demonstrate a unique link between impaired social reward learning and emotional apathy in dementia and reveal a shared neurobiological basis. Greater understanding of these neurocognitive mechanisms of reward processing will help improve the identification of emotional apathy in dementia and inform the development of novel interventions to address these symptoms.