The Effects of Counting the Stride Numbers on the Parkinsonian Gait: Suggesting a Possible Reason for Dual Task Interference

Introduction: Parkinson Disease (PD) is a degenerative and progressive disorder of the central nervous system. It results from degeneration of Substantia Nigra pars compacta (SNc) of the Basal Ganglia (BG). Gait disturbances in PD patients generally get worse over time. The underlying mechanism of gait disturbances in PD has not been elucidated yet. Methods: In this study, we tried to analyze changes in walking performance under both single- and dual-task conditions in people with PD compared to healthy subjects. To this end, the participants’ trunk acceleration signals were recorded under dual-task (counting the stride number while walking) and single-task (walking without performing any other secondary tasks) conditions. Results: The healthy subjects counted the number of their strides correctly; however, 85% of the patients made glaring errors in counting. Then variances of Stride Time Interval (STI) signals were calculated for each participant. STI signals of the patients had a higher variance than that of the healthy subjects in the dual-task condition. Separating the two groups in a dual-task condition is easier. Therefore, we think that the disease sate can be detected in early stages. It is thought that counting is performed independent of walking. Conclusion: PD affects the function of BG that leads to motor timing dysfunction. So, it seems that timing in motor tasks is disrupted while timing in cognitive tasks is not. Therefore, perhaps inconsistency between the two clocks (motor-tasks and cognitive-tasks clocks) is the main cause of dual-task interference in patients’ gait.