Trunk-assisted prehension: specification of body segments with imposed temporal constraints

The authors used a trunk-assisted prehension task to examine intersegment coordination. Participants (N = 7) reached to grasp an object placed beyond full arm extension, thus requiring trunk flexion to achieve the target object, under 4 varying temporal constraints. Kinematic analyses were performed in which the motions of the arm, the trunk, and the endpoint were characterized. The spatial trajectories and the segments' peak velocity data revealed that under high temporal constraints the arm was more responsible for endpoint motion than the trunk, whereas in the unconstrained condition the trunk was more involved. In addition, the arm exhibited a decline in spatial variability toward the end of the movement in all conditions, whereas the trunk did not. The present study is the first to show that when temporal demand is increased for a trunk-assisted prehensile task, the arm plays a larger role than the trunk in the transport of the hand to the object. The data also suggest that the arm participates in the fine accuracy control of the reach, whereas the trunk does not.     

Trunk-Assisted Prehension: Specification of Body Segments With Imposed Temporal Constraints

The authors used a trunk-assisted prehension task to examine intersegment coordination. Participants (N = 7) reached to grasp an object placed beyond full arm extension, thus requiring trunk flexion to achieve the target object, under 4 varying temporal constraints. Kinematic analyses were performed in which the motions of the arm, the trunk, and the endpoint were characterized. The spatial trajectories and the segments' peak velocity data revealed that under high temporal constraints the arm was more responsible for endpoint motion than the trunk, whereas in the unconstrained condition the trunk was more involved. In addition, the arm exhibited a decline in spatial variability toward the end of the movement in all conditions, whereas the trunk did not. The present study is the first to show that when temporal demand is increased for a trunk-assisted prehensile task, the arm plays a larger role than the trunk in the transport of the hand to the object The data also suggest that the arm participates in the fine accuracy control of the reach, whereas the trunk does not.     

Parkinsonian Patients Reduce Their Stroke Size with Increased Processing Demands

Parkinson's disease (PD) patients often show reductions in writing size (micrographia) as the length of the text they produce increases. The cause for these reductions in stroke size are not well understood. Reductions in stroke size could be associated with either concurrent processing demands that result from the coordination and control of fingers, wrist, and arm during writing and the processing of future words or increased extension of the wrist joint as the execution of the writing progresses to the right across the page, resulting in increased stiffness in the pen-limb system. Parkinson's patients and elderly controls wrote phrases of different lengths with target patterns in various serial positions. When the number of words to be written increased, PD patients reduced their stroke size of the initial target pattern, while the elderly controls did not reduce their stroke size. There was no systematic change in stroke size of the second pattern as function of serial position. This result suggests that PD patients reduce the size of their handwriting strokes when concurrent processing load increases.     

Posture based motor planning in a sequential grasping task

Movement planning in sequential tasks is revealed by grasping postures. We explored aspects of planning a sequential drawer opening and object manipulation task with regard to arm and torso postures. We conducted a detailed kinematic analysis of joint postures at the wrist, elbow, and shoulder for a one-grasp and a two-grasp sequence of movement. The second of the two-grasp sequence was constrained (uncomfortable). We predicted that planning for the second grasp in a two-grasp sequence would influence arm, torso, and whole-body postures at the first grasp. Participants prepared for the second grasp by adjusting the posture of the elbow and shoulder and the distance they stepped to the drawer. The joint postures at the elbow and shoulder changed in the direction of the intended object grasp. These findings show that anticipatory adjustments are revealed at postures other than the end-effector and lend insight into the mechanisms of sequential movement planning.     

An experimentally confirmed statistical model on arm movement

The purpose of this research work was to develop a methodology to model arm movement in normal subjects and neurologically impaired individuals through the application of a statistical modelling method. Thirteen subjects with Parkinson's disease and 29 normal controls were recruited to participate in an arm motor task. An infrared optoelectronic kinematic movement analysis system was employed to record arm movement at 50 times per second. This study identified the modified extended Freundlich model as one that could be used to describe this task. Results showed that this model fit the data well and that it has a good correspondence between the observed and the predicted data. However, verification of the model showed that the residuals contained a sizeable autocorrelation factor. The Cochrane and Orcutt method was applied to remove this factor, which improved the fit of the model. Results showed that Parkinson's disease subjects had a higher autocorrelation coefficient than the normal subjects for this task. A positive correlation (r(s) = 0.72, p < 0.001) was found between the Langton-Hewer stage and the autocorrelation coefficient of PD subjects. This finding suggests that if autocorrelation is positively correlated with disease progression, clinicians in their clinical practice might use the autocorrelation value as a useful indicator to quantify the progression of a subjects' disease. Significant differences in model parameters were seen between normal and Parkinson's disease subjects. The use of such a model to represent and quantify movement patterns provides an important base for future study.     

Cognitive slowing in decision tasks in early and advanced Parkinson's disease.

Ten untreated patients with recently diagnosed Parkinson's disease (PD), 9 treated patients with more advanced pathology, and 17 matched normal controls were investigated with three reaction tasks with increasing cognitive load but identical motor requirements: simple reaction, choice reaction with indicative stimuli, and choice reaction with ambiguous stimuli. Times required until a home key was released (= reaction time) and from then until a response key was pressed (= movement time) were recorded. Estimates of pure decision time (overall response time minus movement time in a simple reaction time task) revealed a difference between advanced and early PD patients. Advanced PD patients showed an overall slowing of decision time in the reaction time tasks, but the effect of the cognitive load of the tasks on the decision time was comparable to a control group. The untreated early PD patients performed quite normally in the more simple decision tasks but showed a disproportionate slowing of decision time in tasks with higher cognitive load.     

Achieving Coordination in Prehension: Joint Freezing and Postural Contributions

The focus of the present study was on the intersegmental relationships that emerge when both task and oganismic constraints are imposed upon the coordination system. Seven right-handed subjects were required to reach and grasp a cup (hand transport phase) and place it on a designated target (cup transport phase), using either their preferred or nonpreferred hand. The kinematics of the movement were examined as a function of task (grasping a full cup versus grasping an empty one) and organismic (preferred or nonpreferred hand) constraints. During the hand transport phase, a task constraint effect was revealed through an increase in the low-velocity phase for the full cup condition. This constraint coexisted with a decrease in angular motion of the shoulder and elbow joints, indicating subjects reduced the number of variables to be independently controlled in the final homing-in stage of the movement. Accompanying this decrease in angular change was an increase in the displacement of the trunk. During the cup transport phase, the trunk was shown to contribute significantly more to the movement in the full cup condition and for the left hand movements, thereby increasing the stability of the movement system. These findings are in agreement with Bernstein's (1967) notion of fixating parts of the body as an initial solution to a movement problem, and they lend support to the concept of a proximodistal organization of coordination.     

Preserved and impaired task-switching abilities in non-demented patients with Parkinson's disease

Existing studies on task switching in Parkinson's disease (PD) patients have led to somewhat different results. In particular, it is unclear whether PD patients have a deficit in attentional control. In this study, we assessed task-switching abilities in samples of non-demented PD patients and elderly controls. We used a paradigm in which there was a random task sequence and the task was cued in every trial. This allowed the investigation of both task-set reconfiguration and task-set dissipation. In terms of the proportion of errors made, the patients showed increased switch cost and congruency effects. For reaction times, PD patients showed enlarged congruency effects on switch trials, specifically in the condition in which we used a short constant response-cue interval (RCI). Nevertheless, in a similar fashion to older controls, the patients showed reductions in reaction time switch cost from a short to a long cue-target interval (CTI) and from a short to a long RCI. While these latter findings, respectively, suggest unimpaired task preparation and task dissipation on correct trials in the PD patients, the overall results show that they have a deficit in biasing and selecting currently relevant task sets and more generally argue in favour of a failure of attentional control in PD.     

The impact of Parkinson's disease on sequence learning: perceptual pattern learning and executive function

The current study examined the contribution of brain areas affected by Parkinson's disease (PD) to sequence learning, with a specific focus on response-related processes, spatial attentional control, and executive functioning. Patients with mild PD, patients with moderate PD, and healthy age-matched participants performed three tasks-a sequence learning task with a spatial pattern that was incidental to response selection, a spatial cuing task, and neuropsychological tests of executive function. Whereas moderate PD patients failed to show significant sequence learning, mild PD patients performed comparably with controls. Neither group of PD patients was impaired in the control of spatial attention. Sequence learning was correlated with neuropsychological measures of executive function but not with the ability to control spatial attention. These results suggest that the contribution of the brain areas affected by PD to sequence learning extends beyond motor learning to include the learning of perceptual patterns and involves executive function, including cognitive flexibility and set shifting.     

Evaluating the Acute Contributions of Dopaminergic Replacement to Gait With Obstacles in Parkinson's Disease

The influence of dopaminergic replacement (DR) on gait in people with Parkinson's disease (PD) is well documented. However, little is known about the acute effects of dopamine on more complex locomotor tasks that require visual guidance to avoid obstacles during gait. The authors investigated the influence of DR on locomotor behavior in a task where movement planning and control might be challenged by the height of the obstacle. The PD group included patients diagnosed with idiopathic PD (n = 12), as well as healthy controls (n = 12). Patients walked and stepped over obstacles of different heights before (OFF) and after (ON) levodopa intake. Spatial adjustments were not modulated by DR, but the step time to perform these anticipatory gait adjustments was longer only in PD-OFF (compared with healthy controls) when approaching the highest obstacle, but not PD-ON. During the crossing phase, trail limb toe clearance of PD patients was shorter than healthy controls only during the OFF state. ON-OFF comparisons were significantly different only for the time to reach the lead foot clearance over the highest obstacle. In summary, DR partially improved movement slowness but did not directly affect movement amplitude of lower limb regulation in this gait task.     

Motor deficits in Parkinsonian reaching: dopa-sensitivity influenced by real-world task constraint

Parkinson's disease (PD) patients can perform many daily activities, but movement deficits are evident. Those deficits may be increased when the required movement is constrained in accuracy. Variable improvements in performance with PD medication have been demonstrated, and sensitivity to task constraint has been evident in some studies. The authors quantified both specific movement deficits and improvements for PD patients in a reaching task. PD patients (N=8) both on and off medication showed a need for greater ongoing control in movements with higher task-accuracy constraints. Increased task-accuracy constraints further compromised movement timing and structure among PD patients who were off medication, suggesting that unmedicated PD patients may typically compensate by using more conscious control of movement, resulting in increased slowing and segmentation of components when higher task accuracy is required.     

Learning a pointing task with a kinematically redundant limb: Emerging synergies and patterns of final position variability

The study tested a hypothesis that practice of arm pointing movement can lead to a reorganization of the joint coordination reflected in the emergence of several synergies based on the same set of joints. In particular, involvement of the wrist may represent a choice by the central nervous system and not be driven by the typical “freezing-to-freeing” sequence. The effects of practice on the kinematic patterns and variability of a “fast and accurate” pointing movement using a pointer were studied. An obstacle was placed between the initial position and the target to encourage a curvilinear trajectory and larger wrist involvement. Practice led to a decrease in variability indices accompanied by an increase in movement speed of the endpoint and of the elbow and the shoulder, but not of the wrist joint. Five out of six subjects decreased the peak-to-peak amplitude of wrist motion. Before practice, the variability along the line connecting the endpoint to the shoulder (extent) was similar to that in the direction orthogonal to this line. After practice, variability was reduced along the extent, but not along the orthogonal direction perpendicular to this line. Prior to practice, indices of variability of the endpoint were lower than those of the marker placed over the wrist; after practice, the endpoint showed higher variability indices than the wrist. We interpret the data as consequences of the emergence of two synergies: (a) Pointing with a non-redundant set of the elbow and shoulder joints; and (b) keeping wrist position constant. The former synergy is based on a structural unit involving the elbow and the shoulder, while the latter is based on a structural unit that includes all the major arm joints.     

Movement trajectory smoothness is not associated with the endpoint accuracy of rapid multi-joint arm movements in young and older adults

The minimum variance theory proposes that motor commands are corrupted by signal-dependent noise and smooth trajectories with low noise levels are selected to minimize endpoint error and endpoint variability. The purpose of the study was to determine the contribution of trajectory smoothness to the endpoint accuracy and endpoint variability of rapid multi-joint arm movements. Young and older adults performed arm movements (4 blocks of 25 trials) as fast and as accurately as possible to a target with the right (dominant) arm. Endpoint accuracy and endpoint variability along with trajectory smoothness and error were quantified for each block of trials. Endpoint error and endpoint variance were greater in older adults compared with young adults, but decreased at a similar rate with practice for the two age groups. The greater endpoint error and endpoint variance exhibited by older adults were primarily due to impairments in movement extent control and not movement direction control. The normalized jerk was similar for the two age groups, but was not strongly associated with endpoint error or endpoint variance for either group. However, endpoint variance was strongly associated with endpoint error for both the young and older adults. Finally, trajectory error was similar for both groups and was weakly associated with endpoint error for the older adults. The findings are not consistent with the predictions of the minimum variance theory, but support and extend previous observations that movement trajectories and endpoints are planned independently.     

Posture and the emergence of manual skills

In this paper, we examine how infants’ natural manual and postural activities — what they prefer and do week by week — are related to developmental transitions in reaching skill and its neuromuscular control. Using a dense, longitudinal design, we tracked the manual and postural activities of four infants in a natural, free‐play setting across the first year of life, and related these activities to two transitions in reaching as measured in a structured laboratory setting: the transition to reaching and the transition to stable reaching. Our data indicated that specific advances in the free‐play setting preceded both transitions. Head and upper torso control, the ability to extend the arm and hand to a distant target, and the ability to touch and grasp objects placed nearby were all precursors to the onset of reaching, whereas sitting independently was associated with the transition to stable reaching. We also found important individual variability in when these ‘components’ were in place, indicating that it is the ensemble of components that is essential, not the order in which they develop or the timing of their contribution. These findings suggest that subsequent experimental manipulations should be planned with respect to infants’ individual constellations of skills, rather than looking at only a single precursor to change.     

Testing the effects of end-goal during reach-to-grasp movements in Parkinson’s disease

Previous evidence suggests that hand shaping during reaching is modulated by the presence and the nature of the end-goal following object’s grasp. Here we test whether such modulation is maintained in Parkinson’s disease (PD). Six participants with PD and six healthy participants took part in the study. Participants were requested to reach towards a bottle filled with water, and then: (1) grasp it without performing any subsequent action; (2) grasp it and place it accurately on a target area; (3) grasp it and pour its contents within a container. The results showed that participants shaped their hand differently depending on the presence or absence of an action following object’s grasp. However, the request to perform an action after grasp determined a modulation of hand kinematics which was delayed for PD than for control participants. Further, whereas for control participants the nature of the end-goal determined a modulation of hand shaping, for PD patients such modulation was not evident. Data are discussed in terms of the role played by basal ganglia in implementing anticipatory mechanisms for the control of manipulative activities. We contend that in PD patients these mechanisms are not totally compromised, but their implementation depends on the action information that has to be anticipated.     

Quantitative measurement of handwriting in the assessment of drug-induced parkinsonism

Monitoring drug-induced side effects is especially important for patients who undergo treatment with antipsychotic medications, as these drugs often produce extrapyramidal side effects (EPS) resulting in movement abnormalities similar to parkinsonism. Scientists have developed several objective laboratory tests to measure and research drug-induced movement disorders, but equipment and tests are complex and costly and have not become accepted in large-scale, multi-site clinical trials. The goals of this study were to test whether a simple handwriting measure can discriminate between individuals with psychotropic-induced parkinsonism, Parkinson's disease, and healthy individuals, and to examine some of the psychometric properties of the measure. We examined pen movement kinematics during cursive writing of a standard word in 13 patients with idiopathic Parkinson's disease (PD), 10 schizophrenia patients with drug-induced parkinsonism (SZ), and 12 normal healthy control participants (NC). Participants were instructed to write the word "hello" in cursive twice, at three vertical height scales. Software was used for data acquisition and analysis of vertical stroke velocities, velocity scaling, and smoothness. There were four important results from this study: (1) both SZ patients with drug-induced EPS and PD participants exhibited impaired movement velocities and velocity scaling; (2) performance on the velocity scaling measure distinguished drug-induced EPS from normal with 90% accuracy; (3) SZ, but not PD participants displayed abnormalities in movement smoothness; and (4) there was a positive correlation between age and magnitude of the velocity scaling deficit in PD participants. This study demonstrates that kinematic analyses of pen movements during handwriting may be useful in detecting and monitoring subtle changes in motor control related to the adverse effects of psychotropic medications.     

Prehension and perception of size in left visual neglect

Right hemisphere damaged patients with and without left visual neglect, and age-matched controls had objects of various sizes presented within left or right body hemispace. Subjects were asked to estimate the objects' sizes or to reach out and grasp them, in order to assess visual size processing in perceptual-experiential and action-based contexts respectively. No impairments of size processing were detected in the prehension performance of the neglect patients but a generalised slowing of movement was observed, associated with an extended deceleration phase. Additionally both patient groups reached maximum grip aperture relatively later in the movement than did controls. For the estimation task it was predicted that the left visual neglect group would systematically underestimate the sizes of objects presented within left hemispace but no such abnormalities were observed. Possible reasons for this unexpected null finding are discussed.     

On the nature of fear of falling in Parkinson's disease

In the elderly, fear of falling (FoF) can lead to activity restriction and affect quality of life (QoL). Our aim was to identify the characteristics of FoF in Parkinson's disease and assess its impact on QoL. We assessed FoF in 130 patients with Parkinson's disease (PD) on scales measuring perceived self-efficacy in performing a range of activities (FES), perceived consequences of falling (CoF), and activity avoidance (SAFFE). A significant difference was found in FoF between PD patients who had previously fallen and those who had not and between frequent and infrequent fallers. Patient-rated disability significantly influenced FoF. Difficulty in rising from a chair, difficulty turning, start hesitation, festination, loss of balance, and shuffling were the specific mobility problems which were associated with greater FoF in PD. Disability was the main predictor of FoF, additionally depression predicted perceived consequences of falling, while anxiety predicted activity avoidance. The FoF measures explained 65% of the variance of QoL in PD, highlighting the clinical importance of FoF. These results have implications for the clinical management of FoF in PD.