AUTHOR=Letanneux Alban , Velay Jean-Luc , Viallet François , Pinto Serge 

TITLE=Altered Inhibitory Mechanisms in Parkinson’s Disease: Evidence From Lexical Decision and Simple Reaction Time Tasks

JOURNAL=Frontiers in Human Neuroscience

VOLUME=15

YEAR=2021

URL=https://www.frontiersin.org/journals/human-neuroscience/articles/10.3389/fnhum.2021.624026

DOI=10.3389/fnhum.2021.624026

ISSN=1662-5161

ABSTRACT=<sec><title>Introduction</title><p>Although the motor signs of Parkinson’s disease (PD) are well defined, nonmotor symptoms, including higher-level language deficits, have also been shown to be frequent in patients with PD. In the present study, we used a lexical decision task (LDT) to find out whether access to the mental lexicon is impaired in patients with PD, and whether task performance is affected by bradykinesia.</p></sec><sec><title>Materials and Methods</title><p>Participants were 34 nondemented patients with PD, either without (<italic>off</italic>) medication (<italic>n</italic> = 16) or under optimum (<italic>on</italic>) medication (<italic>n</italic> = 18). A total of 19 age-matched control volunteers were also recruited. We recorded reaction times (RTs) to the LDT and a simple RT (control) task. In each task, stimuli were either visual or auditory. Statistical analyses consisted of repeated-measures analyses of variance and Tukey’s HSD <italic>post hoc</italic> tests.</p></sec><sec><title>Results</title><p>In the LDT, participants with PD both <italic>off</italic> and <italic>on</italic> medication exhibited intact access to the mental lexicon in both modalities. In the visual modality, patients <italic>off</italic> medication were just as fast as controls when identifying real words, but slower when identifying pseudowords. In the visual modality of the control task, RTs for pseudowords were significantly longer for PD patients <italic>off</italic> medication than for controls, revealing an unexpected but significant lexicality effect in patients that was not observed in the auditory modality. Performances of patients <italic>on</italic> medication did not differ from those of age-matched controls.</p></sec><sec><title>Discussion</title><p>Motor execution was not slowed in patients with PD either <italic>off</italic> or <italic>on</italic> medication, in comparison with controls. Regarding lexical access, patients <italic>off</italic> medication seemed to (1) have difficulty inhibiting a cognitive-linguistic process (i.e., reading) when it was not required (simple reaction time task), and (2) exhibit a specific pseudoword processing deficit in the LDT, which may have been related to impaired lateral word inhibition within the mental lexicon. These deficits seemed to be compensated by medication.</p></sec>