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Inter-digit Individuation and Force Variability in the Precision Grip of Young, Elderly, and Parkinson's Disease Participants

David E. Vaillancourt, Andrew B. Slifkin, and Karl M. Newell

We examine the force fluctuations in the control of grip force to determine if force variability increases or decreases in relation to the degree of inter-digit individuation. This relation was examined in young (n = 7) and elderly (n = 7) participants, and in participants diagnosed with Parkinson's disease (n = 7). Force was produced under different force levels (5%, 25%, 50% MVC) with and without visual feedback. Force variability was assessed using the standard deviation and root mean square error, and inter-digit individuation was examined using cross-approximate entropy. Force variability increased with the force level, the removal of visual feedback, and also in the Parkinson's disease compared to the young and elderly matched control participants. There was a reduction in the degree of inter-digit individuation, with increases in force level, the removal of visual feedback, and in Parkinson's disease participants compared to the matched controls. Overall, there was a negative correlation between the degree of inter-digit individuation and force variability. The force fluctuations in precision grip revealed a continuum for the degree of inter-digit individuation in which task constraints, aging, and Parkinson's disease alter the coupling between the digits in controlling grip force.

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Stability of Bimanual Coordination in Parkinson's Disease and Cognitive Modulation of Intention

Reint H. Geuze

The functional integrity of the bimanual neuromotor system of Parkinson's disease (PD) subjects (stage II) compared to controls (2 × n = 16) was evaluated by measures of coordination stability of tapping in in-phase. anti-phase. and 90°-phase. Recently, intentional influence was modeled as an additive attractor function on the intrinsic dynamics, resulting in predictions tested by Scholz and Kelso (1990). In this study, the intentional influence was modulated by attaching cognitive meaning to the rhythmical pattern, which was expected to enhance the stability of coordination and, if effective, might be profitable to PD patients. Half of the PD subjects significantly lacked stability. They were less stable than controls, lost coordination at lower frequencies, and needed more time to switch between phase patterns. The reduction of stability was reflected in the progression of the disease. Cognitive meaning reduced variability of the single hands but not of relative phase, and no effect on switching time was found. The results suggest a weaker coupling strength between the limbs in PD patients lacking stability.

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A Role of the Basal Ganglia in Movement: The Effect of Precues on Discrete Bi-directional Movements in Parkinson's Disease

Andrew M. Johnson, Philip A. Vernon, Quincy J. Almeida, Linda L. Grantier, and Mandar S. Jog

The effect of a precue on improving movement initiation (i.e., reaction time; RT) is well understood, whereas its influence on movement execution (i.e., movement time; MT) has rarely been examined. The current study investigated the influence of a directional precue (i.e., left vs. right) on the RT and MT of simple and discrete bi-directional movements in a large sample of Parkinson's disease patients and healthy control participants. Both patients and controls were tested twice, with testing sessions separated by 2 hours. Patients were tested first following an overnight levodopa withdrawal and again after they had taken their medication. Both patients and controls demonstrated a significant RT improvement when information was provided in advance. MT in both healthy participants and medicated patients was, however, slower with the provision of advance information, while unmedicated patients showed no significant MT effects. These results suggest that while the basal ganglia may not be involved in motor program selection, they may dynamically modulate movement execution.

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Effects of Progressive Resistance Exercise Training on the Motor and Nonmotor Features of Parkinson's Disease: A Review

Guillaume Lamotte, Elizabeth Skender, Miriam R. Rafferty, Fabian J. David, Steve Sadowsky, and Daniel M. Corcos


This paper reviews the therapeutically beneficial effects of progressive resistance exercise training (PRET) on motor and nonmotor symptoms in Parkinson's disease (PD).


First, we perform a systematic review of the literature on the effects of PRET on motor signs of PD, functional outcomes, quality of life, and patient perceived improvement, strength, and cognition in PD. Second, we perform a meta-analysis on the motor section of the UPDRS. Finally, we discuss the results of our review and we identify current knowledge gaps regarding PRET in PD.


This systematic review synthesizes evidence that PRET can improve strength and motor signs of Parkinsonism in PD and may also be beneficial for physical function in individuals with PD. Further research is needed to explore the effects of PRET on nonmotor symptoms such as depression, cognitive impairment, autonomic nervous system dysfunction, and quality of life in individuals with PD.

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Changes in Step Characteristics Over a Known Outdoor Surface Transition: The Effect of Parkinson Disease

Nicholas G. Gomez, Kelton K. Gubler, Kenneth Bo Foreman, and Andrew S. Merryweather

Parkinson disease (PD) is a neurodegenerative disease that affects 3.3% of people over the age of 65. 1 Persons with PD (PwPD) experience a decline in physical coordination and control that can manifest in signs and symptoms that are associated with poor postural control, resting tremors, and gait

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Cross-Sectional Analysis of Backward, Forward, and Dual Task Gait Kinematics in People With Parkinson Disease With and Without Freezing of Gait

Peter S. Myers, Kerri S. Rawson, Elinor C. Harrison, Adam P. Horin, Ellen N. Sutter, Marie E. McNeely, and Gammon M. Earhart

Gait impairments are frequently observed in people with Parkinson disease (PD), increasing fall risk. 1 Such impairments impact forward gait but are often more pronounced during backward and dual task gait. 2 – 4 Gait impairments are often greater among people with PD with freezing of gait

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Stability Boundaries and Lateral Postural Control in Parkinson's Disease

Erwin E.H. van Wegen, Richard E.A. van Emmerik, Robert C. Wagenaar, and Terry Ellis

Postural instability is a major problem in patients with Parkinson's disease (PD). We examined balance control in PD by using center of pressure (CP) variability and time-to-contact to investigate boundary relevant postural control behavior under quiet stance leaning conditions. Postural orientation was manipulated by having patients (n = 10) and healthy older controls (n = 7)lean Forward and backward with varying degrees of lean on a force platform. The subjects were instructed to lean forward or backward (either halfway or as far as possible) without bending their hips or lifting their heels or toes off the ground. Time-to-contact of the CP with the geometric stability boundary defined by the feet as well as CP position and variability were analyzed. Mediolateral CP variability was increased in the patients with PD. Medio-lateral average time-to-contact was decreased in the patients but not so in the antcrior-posterior direction. In contrast to the CP variability, the medio-lateral variability of time-lo-contact was lower in the patients. Patients as well as healthy older controls responded to lean manipulations with an increase in CP variability. Boundary relevant CP measures thus show clear changes in control strategies and confirm the role of lateral instability in PD.

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Provision of External Cues and Movement Sequencing in Parkinson's Disease

Mark A. Rogers, James G. Phillips, John L. Bradshaw, Robert lansek, and Dean Jones

The basal ganglia (BG) may play a part in motor sequencing. Individuals with Parkinson's disease (PD) may exhibit progressive slowing (sequence effect) during motor sequences such as writing (micrographia) and gait. In the present study, a serial two-way choice reaction time task was employed, in which advance information about each next movement was not provided until the participant began moving, thereby assessing the participant's ability to utilize advance information. Participants were 13 individuals with idiopathic PD and 13 age-matched controls. Both PD subjects and controls showed a significant sequence effect in the absence of advance information, possibly reflecting difficulty in initiating and maintaining movement without external cues. PD subjects and controls both exhibited a sequence effect at moderate levels of advance information. At high levels of advance information, PD subjects showed the effect but controls did not, suggesting that controls, unlike PD subjects, were able to use the extra information to facilitate performance, perhaps reflecting more frontal aspects of impairment in PD.

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Pointing to Remembered Targets in 3-D Space in Parkinson's Disease

Howard Poizner, Olga I. Fookson, Michail B. Berkinblit, Wayne Hening, Gregory Feldman, and Sergei Adamovich

A three-dimensional tracking system was used to examine whether subjects with Parkinson's disease (PD) would show characteristic performance deficits in an unconstrained pointing task. Five targets were presented in a pyramidal array in space to 11 individuals with mild to moderate PD and 8 age-matched controls. After the target was indicated, subjects closed their eyes and pointed to the remembered target locations without vision. Despite the absence of visual feedback during movement, PD subjects were as accurate overall as controls. However, PD subjects showed greater variable errors, more irregular trajectories, and a vertical endpoint bias in which their endpoints were significantly lower than controls. They also showed deficiencies in the compensatory organization of joint rotations to ensure consistency in azimuthal (horizontal) positioning of the arm endpoint. We concluded that, under appropriate task conditions, PD subjects may not show overall deficits in accuracy even when making targeted movements at normal speed without visual feedback. Nevertheless, our findings indicate that there are certain dimensions of performance which are selectively altered in Parkinson's disease even when overall performance is normal.

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Comparison of Pallidal and Subthalamic Stimulation on Force Control in Patient's with Parkinson's Disease

Jay L. Alberts, Christopher M. Elder, Michael S. Okun, and Jerrold L. Vitek

The aim of this study was to determine the effects of unilateral deep brain stimulation (DBS) on the control and coordination of grasping forces produced by Parkinson's disease (PD) patients. Ten advanced PD patients with unilateral DBS in the globus pallidus (GPi) or the subthalamic nucleus (STN) (5 patients in each group) performed a functional bimanual dexterous manipulation task. Experiments were performed in the “Off” medication state with DBS “On” and “Off.” DBS resulted in (a) significant clinical improvements, (b) greater maximum grip force for both limbs, (c) reduced movement time, and (d) bilateral coupling of grasping forces. There were no significant differences between the GPi and STN groups for any clinical or kinematic measures. DBS of the GPi and STN leads to an improvement in the motor functioning of advanced PD patients. Improvement in force-timing specification during DBS might allow PD patients to employ a feedforward method of force control.