Coexistent impairments in executive functions and language comprehension in patients with Parkinson's disease (PD) have been repeatedly observed. In this study, the aim was to provide insights into the interaction between linguistic representation and processing and executive functioning. Therefore, sentence comprehension and executive functions were assessed in 28 Dutch-speaking PD patients and 28 healthy control subjects. Three aspects of the sentence materials were varied: (1) phrase structure complexity, (2) sentence length, and (3) picture congruence. PD patients with mild-to-moderate disease severity showed decreased sentence comprehension compared to healthy control subjects. The difficulties encountered by PD patients were not limited to one aspect of the sentence materials. The same pattern of results was present in healthy control subjects. Deficits in set-switching were specifically associated with the comprehension of passive sentences. Generally, our study confirms that there does not appear to be a language faculty encapsulated from the influence of executive functions. 1. Introduction In Parkinson’s disease (PD), the components of the cortico-striato-cortical circuits are not in optimal interaction. Motor symptoms of tremor, bradykinesia, and rigidity are the clinical hallmark of the disease [1]. However, nonmotor symptoms are often present [2]. In particular, cognitive impairments in the domain of executive functioning have frequently been observed even in very early stages of PD [3]. Additionally, several independent researchers have demonstrated a sentence comprehension deficit in PD patients suggesting the involvement of the cortico-striato-cortical circuits in language processing. Since the early 1990s, a number of studies have revealed that long sentences and complex syntactic structures (i.e., noncanonical structures) are vulnerable in individuals with PD (see [4, 5] for a review). There is, however, no consensus concerning the functional basis of the sentence comprehension impairment in PD. Some authors attribute the sentence comprehension deficit to an impairment of grammatical processing as such [6–9]. This viewpoint suggests that linguistic deficits in PD will affect specific aspects of language structure, as in aphasia. Other researchers, however, suggest that executive dysfunction(s) are the functional basis of the sentence comprehension difficulties in PD. This viewpoint suggests that language processing deficits in PD are always associated with executive function deficits. Under this latter view, the language faculty is not
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