The Cognitive Substrates of Action Fluency: A Multivariate Analysis in Parkinson's Disease

Action fluency (AF), the rapid generation of verbs, has been proposed as a sensitive marker of cognitive impairment in Parkinson's disease (PD). However, it is unclear whether AF reflects domain-general executive-generative abilities or a disease-specific motor semantic deficit. This study examined the cognitive predictors of AF in individuals with PD without dementia (PD-ND).

Thirty-one older adults (14 PD-ND, 17 healthy controls) matched on age, sex, and education completed AF, letter fluency, semantic fluency, design fluency, processing speed, and global cognition tasks. AF responses were scored for unique verbs. A multiple regression model examined whether PD status, other fluency scores, processing speed, and global cognition predicted AF performance while controlling for demographic covariates.

Letter, semantic, and design fluency each independently explained variance in AF, whereas processing speed, global cognition, age, education, and PD status were not significant predictors. Thus, group differences between PD-ND and controls were not observed once domain-general fluency abilities were considered.

AF performance in PD-ND reflects domain-general executive-generative mechanisms rather than an isolated verb semantic deficit. Clinically, AF should be interpreted as an integrative measure of executive control. Incorporating a multidimensional fluency battery may improve diagnostic sensitivity and inform targeted interventions for cognitive-communication impairments in PD.