Abstract
Cognitive deficits are common in Parkinson's disease (PD), with some PD patients meeting criteria for mild cognitive impairment (MCI). An unaddressed question is whether linguistic prediction is preserved in PD. This ability is nowadays deemed crucial for achieving fast and efficient comprehension, and it may be negatively impacted by cognitive deterioration in PD. To fill this gap of knowledge, we used event-related potentials (ERPs) to evaluate mechanisms of linguistic prediction in a sample of PD patients (on dopamine compensation) with and without MCI. To this end, participants read sentence contexts that were predictive or not about a sentence-final word. The final word appeared after one sec, matching or mismatching the prediction. The introduction of the interval allowed to capture neural responses both before and after sentence-final words, reflecting semantic anticipation and semantic processing. PD patients with normal cognition (N = 58) showed ERP responses comparable to those of matched controls. Specifically, in predictive contexts, a slow negative potential developed prior to sentence-final words, reflecting semantic anticipation. Later, expected words elicited reduced N400 responses (compared to unexpected words), indicating facilitated semantic processing. PD patients with MCI (N = 20) showed, in addition, a prolongation of the N400 congruency effect (compared to matched PD patients without MCI), indicating that further cognitive decline impacts semantic processing. Finally, lower verbal fluency scores correlated with prolonged N400 congruency effects and with reduced pre-word differences in all PD patients (N = 78). This relevantly points to a role of deficits in temporal-dependent mechanisms in PD, besides prototypical frontal dysfunction, in altered semantic anticipation and semantic processing during sentence comprehension.
Highlights
Parkinson’s disease (PD) is a chronic, neurodegenerative disorder that, in addition to motor defects, involves difficulties in a variety of cognitive domains (Kudlicka et al, 2011; Muslimovic et al, 2005)
Correlational analyses revealed that worse verbal fluency performance was associated with the presence of the event-related potentials (ERPs) pattern observed in the PD-mild cognitive impairment (MCI) group
In PDMCI, further cognitive limitations hinder mechanisms associated with semantic prediction in normal circumstances
Summary
Parkinson’s disease (PD) is a chronic, neurodegenerative disorder that, in addition to motor defects, involves difficulties in a variety of cognitive domains (Kudlicka et al, 2011; Muslimovic et al, 2005). Patients with PD may exhibit significant problems with language comprehension and language production in everyday life. These difficulties have been partly explained by studies that explored in-depth linguistic function in sentence comprehension (for a review, see Pell et al, 2008) and have been mostly attributed to syntactic alterations (Lieberman, 1992; Friederici et al, 2002), there is evidence pointing to slower or delayed lexical and semantic activation (Arnott et al, 2001; Angwin et al, 2005; Angwin et al, 2017). Much evidence of language prediction has been derived from the N400 event-related potential (ERP) component, an index of semantic processing (Kutas et al, 1980). Slow negative potentials (SNP) consistent with semantic anticipation precede sentence-final words in predictive contexts (e.g., before “ball” in "The goalkeeper managed to catch the... ball”) (León-Cabrera et al, 2017; 2019; Grisoni et al, 2017; for a review, see Pullvermüller et al, 2020)
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