Abstract
IntroductionAlthough 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.Materials and MethodsParticipants were 34 nondemented patients with PD, either without (off) medication (n = 16) or under optimum (on) medication (n = 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 post hoc tests.ResultsIn the LDT, participants with PD both off and on medication exhibited intact access to the mental lexicon in both modalities. In the visual modality, patients off 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 off medication than for controls, revealing an unexpected but significant lexicality effect in patients that was not observed in the auditory modality. Performances of patients on medication did not differ from those of age-matched controls.DiscussionMotor execution was not slowed in patients with PD either off or on medication, in comparison with controls. Regarding lexical access, patients off 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.
Highlights
The motor signs of Parkinson’s disease (PD) are well defined, nonmotor symptoms, including higher-level language deficits, have been shown to be frequent in patients with PD
To determine which processes might be affected in patients when it comes to lexical access, we used two tasks that differed on the cognitive/linguistic processes they elicit: an simple reaction time task (SRTT) in which participants had to respond as quickly as possible when the stimulus appeared, whatever its lexical status, and an lexical decision task (LDT), where they had to decide whether the stimulus was a real word or a pseudoword
We found that motor execution per se was not slowed in patients with PD either on or off medication, as they were just as fast as controls in the visual modality when the stimuli were real words
Summary
The motor signs of Parkinson’s disease (PD) are well defined, nonmotor symptoms, including higher-level language deficits, have been shown to be frequent in patients with PD. In terms of language production, individuals with PD appear to produce mainly simple sentences (Illes et al, 1988; Murray, 2000; Murray and Lenz, 2001), punctuated by numerous pauses and presenting many acoustic variations associated with motor speech difficulties (Illes et al, 1988; Illes, 1989) Whether these deficits are caused by a language-specific impairment or more general deficits in other cognitive functions, such as executive functioning or working memory, is an ever present issue for researchers (Lee et al, 2003; Longworth et al, 2005; Terzi et al, 2005; Angwin et al, 2006b; Hochstadt et al, 2006)
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