Speech Motor Deficits in Developmental Stuttering and Parkinson's Disease: From Cellular and Circuit to Network-Level Disruptions.

Speech dysfluency occurs across multiple motor disorders to varying degrees, yet the underlying mechanisms remain incompletely understood. Like locomotion, speech production is relies on basal ganglia circuits, and disruptions in these pathways can lead to varied symptomatic presentations. In this perspective, we discuss evidence from cellular, circuit and network-level studies to highlight shared and disorder-specific mechanisms of speech dysfluency in Parkinson's disease and developmental stuttering. Basal ganglia function and dopaminergic modulation are central to both disorders, while cortical and brainstem microcircuits remain crucial; emerging evidence also implicates astrocytes and inflammatory processes in these conditions. By integrating these multiscale insights, we aim to provide a conceptual framework that explains the mechanistic basis of speech dysfluency in Parkinson's disease and developmental stuttering and identifies avenues for future research and possible therapeutic interventions.