Impaired processing of time-critical language information in Parkinson's disease

BACKGROUND: Parkinson's disease (PD) disturbs basal ganglia functioning and the precise coding of time-critical information. Beyond its known impact on movement capacities, it may therefore affect cognitive functions with high demands of temporal information coordination. We studied this via the processing of syntactic boundaries during auditory sentence parsing. OBJECTIVE: To analyze the processing of syntactic structure as a function of position and duration of prosodic breaks in persons with PD compared to controls. METHODS: 27 persons with PD and 26 healthy controls judged the grammatical correctness of auditorily presented sentences. Prosodic breaks, occurred at syntactically grammatical or ungrammatical positions, with either short or prolonged duration. Accuracy and decision time were analyzed as a function of break position and length. As motor baseline, an auditory reaction time task was included to control for slowness of movement. RESULTS: Persons with PD compared to controls made more errors and slower judgments for both correct and incorrect sentences. For incorrect sentences, however, the prolongation of breaks enhanced the judgment accuracy in PD, eliminating statistical group differences. PD-related abnormalities of task performance were not correlated with the motor severity, duration, or other cognitive aspects of the disease. Prolonged reaction time could not be explained by PD-related motor slowing. CONCLUSION: Impaired temporal sequencing of auditory language input declines sentence parsing in PD. This calls for higher awareness of perceptual deficits of linguistic processing in clinical routine.