Relations between rhythmic impairment in speech and non-verbal domains in Parkinson's disease

Abstract

Rhythmic disorders are common in patients with Parkinson's disease (PD), both in speech (i.e., dysarthria) and in non-verbal rhythmic tasks (e.g., tapping to a beat). However, it is still unknown whether rhythmic disorders in the speech and non-speech domains come from the same source (e.g., an impaired general system for beat perception and production). The goal of this study was to examine the relation between impaired speech rhythm in PD patients and non-speech rhythmic skills. Twenty-two PD patients (mean age: 69.3, SD: 5.5) performed (i) an oral diadochokinesis task, (ii) motor and perceptual non-verbal rhythmic tasks from the BAASTA battery. The patients were divided into two subgroups depending on their performance in the non-verbal rhythmic tasks: good beat-trackers ( n = 12) and poor beat-trackers ( n = 10). The two subgroup of patients were compared in terms of their speech performance. In addition, correlations were run to test the link between speech and non-verbal rhythmic skills. Good beat-trackers showed greater speech-related rhythmic abilities as compared to poor beat-trackers, such as lower variability in producing oral diadochokinesis ( Fig. 1 ), and greater articulatory skills. In addition, the ability to synchronize to a beat was generally correlated with the ability to perform diadochokinesis ( Fig. 2 ). Notably, this link was not confined to tasks involving rhythmic production, but was also apparent between speech production and rhythm perception with non-verbal material ( Fig. 3 ). Our results point to close relations between speech-related rhythmic skills and non-verbal rhythmic motor and perceptual abilities in PD. These findings are consistent with an impaired general system for beat perception and production in PD. This system can be the target of dedicated techniques for rhythmic training (e.g., using non-verbal material) for alleviating some dysarthric symptoms in PD.