Researchers have found that people with Parkinson’s disease exhibit distinct timing patterns in their reaching and stepping movements, and these patterns are influenced differently by medication and auditory cues. The study, published in the journal Scientific Reports, provides insights into the complex relationship between the motor symptoms of Parkinson’s and the underlying neurological changes in the disease. Understanding these timing differences could lead to more targeted interventions and better management of Parkinson’s symptoms. Parkinson’s disease is a neurodegenerative disorder that primarily affects movement, often causing tremors, stiffness, and slowness of movement.
Timing Differences in Parkinson’s Disease
The researchers, led by a team from the University of Ottawa and McGill University, sought to investigate how Parkinson’s disease affects the timing of complex, multi-joint movements in the upper and lower limbs. They had 25 people with Parkinson’s disease and 12 healthy control participants perform two tasks: a repetitive reaching task (RRT) and a stepping-in-place task (SIPT). The participants performed these tasks both with and without auditory cues, and the Parkinson’s group was tested both when they were on and off their dopaminergic medication.
The results revealed some interesting differences in timing between the Parkinson’s and control groups, as well as the effects of medication and cueing.
Medication Slows Down Movement Timing
One unexpected finding was that the Parkinson’s group showed a decrease in their self-selected fastest sustainable movement cadence (speed) when they were on medication, compared to when they were off medication. This is contrary to the typical finding that medication improves bradykinesia (slowness of movement) in Parkinson’s. The researchers suggest this slower cadence may be due to changes in the participants’ internal timing processes, rather than just improvements in motor function.
Cueing Improves Timing Accuracy3>
Interestingly, both the Parkinson’s and control groups showed improved timing accuracy when performing the tasks with auditory cues, compared to the uncued conditions. This suggests that external cues can help compensate for the timing deficits seen in Parkinson’s disease.
Differences in Timing Variability
The researchers also looked at the variability of the participants’ timing, using a statistical model called the Wing-Kristofferson model. This model allows the researchers to separate the variability into two components: clock variance (variability in the internal timing process) and motor variance (variability in the execution of the movement).
The results showed that the Parkinson’s group had increased clock variance compared to the control group, particularly when they were on medication and performing the reaching task without cues. This suggests that the internal timing processes are impaired in Parkinson’s disease, and that medication may interact with this impairment in complex ways.
Implications and Future Research
These findings highlight the importance of considering the timing and coordination of complex movements, not just the speed or accuracy, when assessing and treating the motor symptoms of Parkinson’s disease. The researchers note that the standard measures of timing variability may not fully capture the timing deficits in Parkinson’s, and that more sophisticated models like the Wing-Kristofferson approach are needed.
Future research could explore the relationship between these timing deficits and other aspects of Parkinson’s, such as gait problems and freezing of movement. Additionally, investigating how different types of cues or rehabilitation strategies might target the timing impairments could lead to more effective interventions for managing the motor symptoms of Parkinson’s disease.
Author credit: This article is based on research by Allen Hill, Hiram Cantú, Julie N. Côté, Julie Nantel.
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