Abstract
In addition to the typical motor symptoms, a majority of patients suffering from Parkinson's disease experience language impairments. Deep Brain Stimulation of the subthalamic nucleus robustly reduces motor dysfunction, but its impact on language skills remains ambiguous. To elucidate the impact of subthalamic deep brain stimulation on natural language production, we systematically analyzed language samples from fourteen individuals (three female / eleven male, average age 66.43 ± 7.53 years) with Parkinson's disease in the active (ON) versus inactive (OFF) stimulation condition. Significant ON-OFF differences were considered as stimulation effects. To localize their neuroanatomical origin within the subthalamic nucleus, they were correlated with the volume of tissue activated by therapeutic stimulation. Word and clause production speed increased significantly under active stimulation. These enhancements correlated with the volume of tissue activated within the associative part of the subthalamic nucleus, but not with that within the dorsolateral motor part, which again correlated with motor improvement. Language error rates were lower in the ON vs. OFF condition, but did not correlate with electrode localization. No significant changes in further semantic or syntactic language features were detected in the current study. The findings point towards a facilitation of executive language functions occurring rather independently from motor improvement. Given the presumed origin of this stimulation effect within the associative part of the subthalamic nucleus, this could be due to co-stimulation of the prefrontal-subthalamic circuit.
Highlights
Apart from disabling motor symptoms, Parkinson’s disease (PD) can lead to wide-ranging non-motor symptoms [1]
Word and clause production speed increased significantly under active stimulation. These enhancements correlated with the volume of tissue activated within the associative part of the subthalamic nucleus, but not with that within the dorsolateral motor part, which again correlated with motor improvement
Regarding effects of subthalamic nucleus (STN) Deep Brain Stimulation (DBS) on natural language production, only a few studies have been conducted and delivered equivocal results: [50,51,52,53,54] whereas reduced hesitations, paraphasias, and errors together with improved lexical retrieval were interpreted as a functional recovery [55], other studies showed vastly unaltered language functions [53, 56] or compromised grammatical capacities [52]. Since this heterogeneity could relate to differences between language tasks as well as the impact of variable stimulation fields [57], the current study aims to analyze a comprehensive range of linguistic parameters in spontaneous language samples from persons with PD with respect to the volume of tissue activated (VAT) by STN DBS
Summary
Apart from disabling motor symptoms, Parkinson’s disease (PD) can lead to wide-ranging non-motor symptoms [1]. These involve cognitive processes [2] which typically affect functions relevant to language such as memory, set shifting, flexibility, planning, and the integration of semantic networks [3,4,5]. The majority of PD patients develop language symptoms including impaired fluency [6,7,8,9] (for reviews see [10]) with an increase in speech hesitations [11], and slower speech initiation [12]. In addition to the typical motor symptoms, a majority of patients suffering from Parkinson’s disease experience language impairments. Deep Brain Stimulation of the subthalamic nucleus robustly reduces motor dysfunction, but its impact on language skills remains ambiguous
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