Parkinson's disease speech production network as determined by graph-theoretical network analysis

Author Summary Parkinson's disease (PD) features a variety of motor and nonmotor symptoms, which relate to changes in functional brain connectivity. This study investigated how the whole-brain speech production network (SPN) is affected by PD. The paradigm included an emotional distraction component to assess the SPN's susceptibility to an emotional influence. The SPN was found to be less integrated and less segregated in PD than in healthy controls. Emotional distraction had a greater effect on the SPN in PD than in healthy controls. Key nodes for information flow (network pillars) were mainly located in associative cortices. They were robust against emotional distraction in healthy controls, but shifted to primary and secondary cortical areas in PD. Parkinson's disease (PD) can affect speech as well as emotion processing. We employ whole-brain graph-theoretical network analysis to determine how the speech-processing network (SPN) changes in PD, and assess its susceptibility to emotional distraction. Functional magnetic resonance images of 14 patients (aged 59.6 +/- 10.1 years, 5 female) and 23 healthy controls (aged 64.1 +/- 6.5 years, 12 female) were obtained during a picture-naming task. Pictures were supraliminally primed by face pictures showing either a neutral or an emotional expression. PD network metrics were significantly decreased (mean nodal degree, p < 0.0001; mean nodal strength, p < 0.0001; global network efficiency, p < 0.002; mean clustering coefficient, p < 0.0001), indicating an impairment of network integration and segregation. There was an absence of connector hubs in PD. Controls exhibited key network hubs located in the associative cortices, of which most were insusceptible to emotional distraction. The PD SPN had more key network hubs, which were more disorganized and shifted into auditory, sensory, and motor cortices after emotional distraction. The whole-brain SPN in PD undergoes changes that result in (a) decreased network integration and segregation, (b) a modularization of information flow within the network, and (c) the inclusion of primary and secondary cortical areas after emotional distraction.