Effects of a moving target versus a temporal constraint on reach and grasp in patients with Parkinson's disease

Exploration of sensory-motor tradeoff behavior in Parkinson’s disease

While slowness of movement is an obligatory characteristic of Parkinson’s disease (PD), there are conditions in which patients move uncharacteristically fast, attributed to deficient motor inhibition. Here we investigate deficient inhibition in an optimal sensory-motor integration framework, using a game in which subjects used a paddle to catch a virtual ball. Display of the ball was extinguished as soon as the catching movement started, segregating the task into a sensing and acting phase. We analyzed the behavior of 9 PD patients (ON medication) and 10 age-matched controls (HC). The switching times (between sensing and acting phase) were compared to the predicted optimal switching time, based on the individual estimates of sensory and motor uncertainties. The comparison showed that deviation from predicted optimal switching times were similar between groups. However, PD patients showed a weaker correlation between variability in switching time and sensory-motor uncertainty, indicating a reduced propensity to generate exploratory behavior for optimizing goal-directed movements. Analysis of the movement kinematics revealed that PD patients, compared to controls, used a lower peak velocity of the paddle and intercepted the ball with greater velocity. Adjusting the trial duration to the time for the paddle to stop moving, we found that PD patients spent a smaller proportion of the trial duration for observing the ball. Altogether, the results do not show the premature movement initiation and truncated sensory processing that we predicted to ensue from deficient inhibition in PD.

Reaching and Grasping Movements in Parkinson's Disease: A Review

Parkinson's disease (PD) is known to affect the brain motor circuits involving the basal ganglia (BG) and to induce, among other signs, general slowness and paucity of movements. In upper limb movements, PD patients show a systematic prolongation of movement duration while maintaining a sufficient level of endpoint accuracy. PD appears to cause impairments not only in movement execution, but also in movement initiation and planning, as revealed by abnormal preparatory activity of motor-related brain areas. Grasping movement is affected as well, particularly in the coordination of the hand aperture with the transport phase. In the last fifty years, numerous behavioral studies attempted to clarify the mechanisms underlying these anomalies, speculating on the plausible role that the BG-thalamo-cortical circuitry may play in normal and pathological motor control. Still, many questions remain open, especially concerning the management of the speed-accuracy tradeoff and the online feedback control. In this review, we summarize the literature results on reaching and grasping in parkinsonian patients. We analyze the relevant hypotheses on the origins of dysfunction, by focusing on the motor control aspects involved in the different movement phases and the corresponding role played by the BG. We conclude with an insight into the innovative stimulation techniques and computational models recently proposed, which might be helpful in further clarifying the mechanisms through which PD affects reaching and grasping movements.

Influence of alarming auditory cues on viscoelastic stiffness of skeletal muscles in patients with Parkinson's disease

BACKGROUND

Patients with Parkinson's disease can show brief normalization of motor activity in response to intense external stimuli - a phenomenon known as paradoxical kinesis. The purpose of the present study was to examine the effect of alarming auditory signals on the level of viscoelastic stiffness of skeletal muscles as an indicator of parkinsonian rigidity.

METHODS

Myotonometry was used to determine the changes of viscoelastic stiffness of skeletal muscles in ten patients in an advanced stage of Parkinson's disease, treated with deep brain stimulation, and ten healthy controls. The measurements were repeated and compared during the stimulation-on and stimulation-off periods, with and without auditory alarming signals.

FINDINGS

The mean values of stiffness measured in the stimulation-off phase (370.4 N/m) were significantly higher than the values obtained in the stimulation-on phase (339.2 N/m) (q = 6.05; P < 0.01) but also in the stimulation-off with alarming signals phase (349.6 N/m) (q = 4.04; P < 0.05). In the normal controls, exposure to the auditory alarming signals did not change the values of viscoelastic stiffness.

INTERPRETATION

These findings demonstrate that the phenomenon of paradoxical kinesis is associated with the changes of muscular rigidity in parkinsonian patients. Results from the study may help to establish new strategies for addressing motor disabilities in patients with Parkinson's disease.

Paradoxical kinesia in Parkinson's disease revisited: Anticipation of temporal constraints is critical

Slowness of movement, called bradykinesia is the cardinal symptom of Parkinson's disease. Under distinct but not yet well-defined circumstances, patients with Parkinson's disease are able to overcome bradykinesia. One common hypothesis for this phenomenon termed paradoxical kinesia in Parkinson's disease postulates that the presentation of external sensory triggers is pivotal to elicit significant increase of motor velocity. In the present study, we examined an alternative hypothesis, namely that an internal cue in the absence of sensory cues are linked to paradoxical kinesia. To test this alternative hypothesis, patients with Parkinson's disease and healthy age-matched controls (n=9 per group) performed two movement tasks. In the stationary-object prehension task, subjects had to pick up a stationary target object. For the escaping-object task, the participants had to pick up the target object before it moved out of reach. The time available to reach for the object was adjusted individually to ensure comparable difficulty across participants. Reaction time, movement duration, and maximum velocity were assessed for both movement tasks. In Parkinson's disease patients and healthy controls, anticipation of the imminent movement of a target object significantly decreased reaction time, movement duration, and increased maximum movement velocity. The increase of maximum movement velocity in the escape-condition was significantly more pronounced for Parkinson's disease patients as compared to healthy controls. We provide evidence that internal cues such as temporal constraints are sufficient to diminish the cardinal clinical symptom of bradykinesia in Parkinson's disease. Our results suggest that expectations rather than sensory cues are critical for the emergence of paradoxical kinesia and we discuss the implications of our findings for an account of paradoxical kinesia.

Motivational Modulation of Self-Initiated and Externally Triggered Movement Speed Induced by Threat of Shock: Experimental Evidence for Paradoxical Kinesis in Parkinson's Disease

Background

Paradoxical kinesis has been observed in bradykinetic people with Parkinson’s disease. Paradoxical kinesis occurs in situations where an individual is strongly motivated or influenced by relevant external cues. Our aim was to induce paradoxical kinesis in the laboratory. We tested whether the motivation of avoiding a mild electric shock was sufficient to induce paradoxical kinesis in externally-triggered and self-initiated conditions in people with Parkinson’s disease tested on medication and in age-matched controls.

Methods

Participants completed a shock avoidance behavioural paradigm in which half of the trials could result in a mild electric shock if the participant did not move fast enough. Half of the trials of each type were self-initiated and half were externally-triggered. The criterion for avoiding shock was a maximum movement time, adjusted according to each participant’s performance on previous trials using a staircase tracking procedure.

Results

On trials with threat of shock, both patients with Parkinson’s disease and controls had faster movement times compared to no potential shock trials, in both self-initiated and externally-triggered conditions. The magnitude of improvement of movement time from no potential shock to potential shock trials was positively correlated with anxiety ratings.

Conclusions

When motivated to avoid mild electric shock, patients with Parkinson’s disease, similar to healthy controls, showed significant speeding of movement execution. This was observed in both self-initiated and externally-triggered versions of the task. Nevertheless, in the ET condition the improvement of reaction times induced by motivation to avoid shocks was greater for the PD patients than controls, highlighting the value of external cues for movement initiation in PD patients. The magnitude of improvement from the no potential shock to the potential shock trials was associated with the threat-induced anxiety. This demonstration of paradoxical kinesis in the laboratory under both self-initiated and externally-triggered conditions has implications for motivational and attentional enhancement of movement speed in Parkinson’s disease.

Muscle co-activity tuning in Parkinsonian hand movement: disease-specific changes at behavioral and cerebral level

We investigated simple directional hand movements based on different degrees of muscle co-activity, at behavioral and cerebral level in healthy subjects and Parkinson's disease (PD) patients. We compared “singular” movements, dominated by the activity of one agonist muscle, to “composite” movements, requiring conjoint activity of multiple muscles, in a center-out (right hand) step-tracking task. Behavioral parameters were obtained by EMG and kinematic recordings. fMRI was used to investigate differences in underlying brain activations between PD patients (N = 12) and healthy (age-matched) subjects (N = 18). In healthy subjects, composite movements recruited the striatum and cortical areas comprising bilaterally the supplementary motor area and premotor cortex, contralateral medial prefrontal cortex, primary motor cortex, primary visual cortex, and ipsilateral superior parietal cortex. Contrarily, the ipsilateral cerebellum was more involved in singular movements. This striking dichotomy between striatal and cortical recruitment vs. cerebellar involvement was considered to reflect the complementary roles of these areas in motor control, in which the basal ganglia are involved in movement selection and the cerebellum in movement optimization. Compared to healthy subjects, PD patients showed decreased activation of the striatum and cortical areas in composite movement, while performing worse at behavioral level. This implies that PD patients are especially impaired on tasks requiring highly tuned muscle co-activity. Singular movement, on the other hand, was characterized by a combination of increased activation of the ipsilateral parietal cortex and left cerebellum. As singular movement performance was only slightly compromised, we interpret this as a reflection of increased visuospatial processing, possibly as a compensational mechanism.

Increasing speed to improve arm movement and standing postural control in Parkinson's disease patients when catching virtual moving balls

Research has shown that moving targets help Parkinson's disease (PD) patients improve their arm movement while sitting. We examined whether increasing the speed of a moving ball would also improve standing postural control in PD patients during a virtual reality (VR) ball-catching task. Twenty-one PD patients and 21 controls bilaterally reached to catch slow-moving and then fast-moving virtual balls while standing. A projection-based VR system connected to a motion-tracking system and a force platform was used. Dependent measures included the kinematics of arm movement (movement time, peak velocity), duration of anticipatory postural adjustments (APA), and center of pressure (COP) movement (movement time, maximum amplitude, and average velocity). When catching a fast ball, both PD and control groups made arm movements with shorter movement time and higher peak velocity, longer APA, as well as COP movements with shorter movement time and smaller amplitude than when catching a slow ball. The change in performance from slow- to fast-ball conditions was not different between the PD and control groups. The results suggest that raising the speed of virtual moving targets should increase the speed of arm and COP movements for PD patients. Therapists, however, should also be aware that a fast virtual moving target causes the patient to confine the COP excursion to a smaller amplitude. Future research should examine the effect of other task parameters (e.g., target distance, direction) on COP movement and examine the long-term effect of VR training.

Sensory-motor problems in Autism

Despite being largely characterized as a social and cognitive disorder, strong evidence indicates the presence of significant sensory-motor problems in Autism Spectrum Disorder (ASD). This paper outlines our progression from initial, broad assessment using the Movement Assessment Battery for Children (M-ABC2) to subsequent targeted kinematic assessment. In particular, pronounced ASD impairment seen in the broad categories of manual dexterity and ball skills was found to be routed in specific difficulties on isolated tasks, which were translated into focused experimental assessment. Kinematic results from both subsequent studies highlight impaired use of perception-action coupling to guide, adapt and tailor movement to task demands, resulting in inflexible and rigid motor profiles. In particular difficulties with the use of temporal adaption are shown, with "hyperdexterity" witnessed in ballistic movement profiles, often at the cost of spatial accuracy and task performance. By linearly progressing from the use of a standardized assessment tool to targeted kinematic assessment, clear and defined links are drawn between measureable difficulties and underlying sensory-motor assessment. Results are specifically viewed in-light of perception-action coupling and its role in early infant development suggesting that rather than being "secondary" level impairment, sensory-motor problems may be fundamental in the progression of ASD. This logical and systematic process thus allows a further understanding into the potential root of observable motor problems in ASD; a vital step if underlying motor problems are to be considered a fundamental aspect of autism and allow a route of non-invasive preliminary diagnosis.

A fast-moving target in the Valpar assembly task improved unimanual and bimanual movements in patients with schizophrenia

PURPOSE

To investigate the effects of target speed on unimanual and bimanual movements during a bimanual prehension and assembly task in patients with mild schizophrenia and healthy controls.

METHOD

Fifteen patients with schizophrenia and 15 age- and gender-matched healthy controls were instructed to reach and assemble spacers with both hands for a target that moved at two speeds: fast or slow. Dependent variables were movement kinematics: movement time, number of movement units and timing intervals between both hands.

RESULTS

A fast-moving target induced shorter movement times, fewer movement units and shorter timing intervals than did a slow-moving target for patients. Under the slow-target condition, patients had longer movement times and a longer timing interval during prehension, as well as longer movement times, more movement units and a longer timing interval during assembly than did controls. Under the fast-target condition, patients still had slower and less-synchronized prehension than did controls, but their assembly improved to a level similar to that of controls.

CONCLUSIONS

A fast-moving target induced faster, smoother and more synchronized movements than did a slow-moving target for patients with schizophrenia, especially during assembly.

IMPLICATIONS FOR REHABILITATION

A fast-moving target might elicit faster, smoother, and more synchronized movements than might a slow-moving target during a bimanual assembly task for patients with mild schizophrenia. The findings of impaired movement kinematics under the slow-target condition suggest that patients with schizophrenia need movement training.

Trunk-arm coordination in reaching for moving targets in people with Parkinson's disease: comparison between virtual and physical reality

We used a trunk-assisted prehension task to examine the effect of task (reaching for stationary vs. moving targets) and environmental constraints (virtual reality [VR] vs. physical reality) on the temporal control of trunk and arm motions in people with Parkinson's disease (PD). Twenty-four participants with PD and 24 age-matched controls reached for and grasped a ball that was either stationary or moving along a ramp 120% of arm length away. In a similar VR task, participants reached for a virtual ball that was either stationary or moving. Movement speed was measured as trunk and arm movement times (MTs); trunk-arm coordination was measured as onset interval and offset interval between trunk and arm motions, as well as a summarized index-desynchrony score. In both VR and physical reality, the PD group had longer trunk and arm MTs than the control group when reaching for stationary balls (p<.001). When reaching for moving balls in VR and physical reality, however, the PD group had lower trunk and arm MTs, onset intervals, and desynchrony scores (p<.001). For the PD group, VR induced shorter trunk MTs, shorter offset intervals, and lower desynchrony scores than did physical reality when reaching for moving balls (p<.001). These findings suggest that using real moving targets in trunk-assisted prehension tasks improves the speed and synchronization of trunk and arm motions in people with PD, and that using virtual moving targets may induce a movement termination strategy different from that used in physical reality.

Upper Extremity Motor Learning among Individuals with Parkinson's Disease: A Meta-Analysis Evaluating Movement Time in Simple Tasks

Motor learning has been found to occur in the rehabilitation of individuals with Parkinson's disease (PD). Through repetitive structured practice of motor tasks, individuals show improved performance, confirming that motor learning has probably taken place. Although a number of studies have been completed evaluating motor learning in people with PD, the sample sizes were small and the improvements were variable. The purpose of this meta-analysis was to determine the ability of people with PD to learn motor tasks. Studies which measured movement time in upper extremity reaching tasks and met the inclusion criteria were included in the analysis. Results of the meta-analysis indicated that people with PD and neurologically healthy controls both demonstrated motor learning, characterized by a decrease in movement time during upper extremity movements. Movement time improvements were greater in the control group than in individuals with PD. These results support the findings that the practice of upper extremity reaching tasks is beneficial in reducing movement time in persons with PD and has important implications for rehabilitation.

Impairment of gradual muscle adjustment during wrist circumduction in Parkinson's disease

Purposeful movements are attained by gradually adjusted activity of opposite muscles, or synergists. This requires a motor system that adequately modulates initiation and inhibition of movement and selectively activates the appropriate muscles. In patients with Parkinson's disease (PD) initiation and inhibition of movements are impaired which may manifest itself in e.g. difficulty to start and stop walking. At single-joint level, impaired movement initiation is further accompanied by insufficient inhibition of antagonist muscle activity. As the motor symptoms in PD primarily result from cerebral dysfunction, quantitative investigation of gradually adjusted muscle activity during execution of purposeful movement is a first step to gain more insight in the link between impaired modulation of initiation and inhibition at the levels of (i) cerebrally coded task performance and (ii) final execution by the musculoskeletal system. To that end, the present study investigated changes in gradual adjustment of muscle synergists using a manipulandum that enabled standardized smooth movement by continuous wrist circumduction. Differences between PD patients (N = 15, off-medication) and healthy subjects (N = 16) concerning the relation between muscle activity and movement performance in these groups were assessed using kinematic and electromyographic (EMG) recordings. The variability in the extent to which a particular muscle was active during wrist circumduction--defined as muscle activity differentiation--was quantified by EMG. We demonstrated that more differentiated muscle activity indeed correlated positively with improved movement performance, i.e. higher movement speed and increased smoothness of movement. Additionally, patients employed a less differentiated muscle activity pattern than healthy subjects. These specific changes during wrist circumduction imply that patients have a decreased ability to gradually adjust muscles causing a decline in movement performance. We propose that less differentiated muscle use in PD patients reflects impaired control of modulated initiation and inhibition due to decreased ability to selectively and jointly activate muscles.

Comparison of virtual reality versus physical reality on movement characteristics of persons with Parkinson's disease: effects of moving targets

OBJECTIVE

To compare the performance of reaching for stationary and moving targets in virtual reality (VR) and physical reality in persons with Parkinson's disease (PD).

DESIGN

A repeated-measures design in which all participants reached in physical reality and VR under 5 conditions: 1 stationary ball condition and 4 conditions with the ball moving at different speeds.

SETTING

University research laboratory.

PARTICIPANTS

Persons with idiopathic PD (n=29) and age-matched controls (n=25).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Success rates and kinematics of arm movement (movement time, amplitude of peak velocity, and percentage of movement time for acceleration phase).

RESULTS

In both VR and physical reality, the PD group had longer movement time (P<.001) and lower peak velocity (P<.001) than the controls when reaching for stationary balls. When moving targets were provided, the PD group improved more than the controls did in movement time (P<.001) and peak velocity (P<.001), and reached a performance level similar to that of the controls. Except for the fastest moving ball condition (0.5-s target viewing time), which elicited worse performance in VR than in physical reality, most cueing conditions in VR elicited performance generally similar to those in physical reality.

CONCLUSIONS

Although slower than the controls when reaching for stationary balls, persons with PD increased movement speed in response to fast moving balls in both VR and physical reality. This suggests that with an appropriate choice of cueing speed, VR is a promising tool for providing visual motion stimuli to improve movement speed in persons with PD. More research on the long-term effect of this type of VR training program is needed.

Effects of virtual reality training on functional reaching movements in people with Parkinson’s disease: a randomized controlled pilot trial

Objective: To investigate whether practising reaching for virtual moving targets would improve motor performance in people with Parkinson’s disease.

Design: Randomized pretest–posttest control group design.

Setting: A virtual reality laboratory in a university setting.

Participants: Thirty-three adults with Parkinson’s disease.

Interventions: The virtual reality training required 60 trials of reaching for fast-moving virtual balls with the dominant hand. The control group had 60 practice trials turning pegs with their non-dominant hand.

Main outcome measures: Pretest and posttest required reaching with the dominant hand to grasp real stationary balls and balls moving at different speeds down a ramp. Success rates and kinematic data (movement time, peak velocity and percentage of movement time for acceleration phase) from pretest and posttest were recorded to determine the immediate transfer effects.

Results: Compared with the control group, the virtual reality training group became faster ( F = 9.08, P = 0.005) and more forceful ( F = 9.36, P = 0.005) when reaching for real stationary balls. However, there was no significant difference in success rate or movement kinematics between the two groups when reaching for real moving balls.

Conclusion: A short virtual reality training programme improved the movement speed of discrete aiming tasks when participants reached for real stationary objects. However, the transfer effect was minimal when reaching for real moving objects.

Reduced muscle power is associated with slower walking velocity and falls in people with Parkinson's disease

PURPOSE

Muscle strength (force) and power (force x velocity) are reduced in Parkinson's disease (PD). Reduced muscle power is associated with slower walking velocity and falls in the older population, but these associations in people with PD have not previously been investigated. This study investigated the relationships between leg extensor muscle power and strength with walking speed and past falls in people with PD.

PARTICIPANTS AND METHODS

Forty people with mild to moderate PD were assessed. Walking velocity was measured over 10 m and the number of falls the participant reported having in the past 12 months was recorded. Leg extensor muscle power and strength were measured using a Keiser leg press machine.

RESULTS

Muscle power explained more than half of the variance (R(2) = 0.54) in walking velocity and remained significantly (p < 0.05) associated with walking velocity in models which included Unified Parkinson's Disease Rating Scale (UPDRS) motor scores. Participants with low muscle power were 6 times more likely to report multiple falls in the past year than those with high muscle power (OR = 6.0, 95% CI 1.1 to 33.3), though this association between falls and power was no longer significant in models which included UPDRS motor scores (p = 0.09).

CONCLUSION

Muscle power is a significant determinant of walking velocity in PD even after adjusting for UPDRS motor score. Muscle power training warrants investigation in people with PD.