Deficits in rapid adjustments of movements according to task constraints in Parkinson's disease

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.

Impact of Parkinson's disease on proprioceptively based on-line movement control

Evidence suggests that Parkinson's disease (PD) patients produce large spatial errors when reaching to proprioceptively defined targets. Here, we examined whether these movement inaccuracies result mainly from impaired use of proprioceptive inputs for movement planning mechanisms or from on-line movement guidance. Medicated and non-medicated PD patients and healthy controls performed three-dimensional reaching movements in four sensorimotor conditions that increase proprioceptive processing requirements. We assessed the influence of these sensorimotor conditions on the final accuracy and initial kinematics of the movements. If the patterns of final errors are primarily determined by planning processes before the initiation of the movement, the initial kinematics of reaching movements should show similar trends and predict the pattern of final errors. Medicated and non-medicated PD patients showed a greater mean level of final 3D errors than healthy controls when proprioception was the sole source of information guiding the movement, but this difference reached significance only for medicated PD patients. However, the pattern of initial kinematics and final spatial errors were markedly different both between sensorimotor conditions and between groups. Furthermore, medicated and non-medicated PD patients were less efficient than healthy controls in compensating for their initial spatial errors (hand distance from target location at peak velocity) when aiming at proprioceptively defined compared to visually defined targets. Considered together, the results are consistent with a selective deficit in proprioceptively based movement guidance in PD. Furthermore, dopaminergic medication did not improve proprioceptively guided movements in PD patients, indicating that dopaminergic dysfunction within the basal ganglia is not solely responsible for these deficits.

Parkinson's disease patients show impaired corrective grasp control and eye-hand coupling when reaching to grasp virtual objects

The effect of Parkinson's disease (PD) on hand-eye coordination and corrective response control during reach-to-grasp tasks remains unclear. Moderately impaired PD patients (n=9) and age-matched controls (n=12) reached to and grasped a virtual rectangular object, with haptic feedback provided to the thumb and index fingertip by two 3-degree of freedom manipulanda. The object rotated unexpectedly on a minority of trials, requiring subjects to adjust their grasp aperture. On half the trials, visual feedback of finger positions disappeared during the initial phase of the reach, when feedforward mechanisms are known to guide movement. PD patients were tested without (OFF) and with (ON) medication to investigate the effects of dopamine depletion and repletion on eye-hand coordination online corrective response control. We quantified eye-hand coordination by monitoring hand kinematics and eye position during the reach. We hypothesized that if the basal ganglia are important for eye-hand coordination and online corrections to object perturbations, then PD patients tested OFF medication would show reduced eye-hand spans and impoverished arm-hand coordination responses to the perturbation, which would be further exasperated when visual feedback of the hand was removed. Strikingly, PD patients tracked their hands with their gaze, and their movements became destabilized when having to make online corrective responses to object perturbations exhibiting pauses and changes in movement direction. These impairments largely remained even when tested in the ON state, despite significant improvement on the Unified Parkinson's Disease Rating Scale. Our findings suggest that basal ganglia-cortical loops are essential for mediating eye-hand coordination and adaptive online responses for reach-to-grasp movements, and that restoration of tonic levels of dopamine may not be adequate to remediate this coordinative nature of basal ganglia-modulated function.

Spatial-orientation priming impedes rather than facilitates the spontaneous control of hand-retraction speeds in patients with Parkinson's disease

Background

Often in Parkinson’s disease (PD) motor-related problems overshadow latent non-motor deficits as it is difficult to dissociate one from the other with commonly used observational inventories. Here we ask if the variability patterns of hand speed and acceleration would be revealing of deficits in spatial-orientation related decisions as patients performed a familiar reach-to-grasp task. To this end we use spatial-orientation priming which normally facilitates motor-program selection and asked whether in PD spatial-orientation priming helps or hinders performance.

Methods

To dissociate spatial-orientation- and motor-related deficits participants performed two versions of the task. The biomechanical version (DEFAULT) required the same postural- and hand-paths as the orientation-priming version (primed-UP). Any differences in the patients here could not be due to motor issues as the tasks were biomechanically identical. The other priming version (primed-DOWN) however required additional spatial and postural processing. We assessed in all three cases both the forward segment deliberately aimed towards the spatial-target and the retracting segment, spontaneously bringing the hand to rest without an instructed goal.

Results and Conclusions

We found that forward and retracting segments belonged in two different statistical classes according to the fluctuations of speed and acceleration maxima. Further inspection revealed conservation of the forward (voluntary) control of speed but in PD a discontinuity of this control emerged during the uninstructed retractions which was absent in NC. Two PD groups self-emerged: one group in which priming always affected the retractions and the other in which only the more challenging primed-DOWN condition was affected. These PD-groups self-formed according to the speed variability patterns, which systematically changed along a gradient that depended on the priming, thus dissociating motor from spatial-orientation issues. Priming did not facilitate the motor task in PD but it did reveal a breakdown in the spatial-orientation decision that was independent of the motor-postural path.

The interaction of postural and voluntary strategies for stability in Parkinson's disease

This study assessed the effects of stability constraints of a voluntary task on postural responses to an external perturbation in subjects with Parkinson's disease (PD) and healthy elderly participants. Eleven PD subjects and twelve control subjects were perturbed with backward surface translations while standing and performing two versions of a voluntary task: holding a tray with a cylinder placed with the flat side down [low constraint (LC)] or with the rolling, round side down [high constraint (HC)]. Participants performed alternating blocks of LC and HC trials. PD participants accomplished the voluntary task as well as control subjects, showing slower tray velocity in the HC condition compared with the LC condition. However, the latency of postural responses was longer in the HC condition only for control subjects. Control subjects presented different patterns of hip-shoulder coordination as a function of task constraint, whereas PD subjects had a relatively invariant pattern. Initiating the experiment with the HC task led to 1) decreased postural stability in PD subjects only and 2) reduced peak hip flexion in control subjects only. These results suggest that PD impairs the capacity to adapt postural responses to constraints imposed by a voluntary task.

Human basal ganglia and the dynamic control of force during on-line corrections

Natural movements are corrected in part by the generation of submovements, occurring early in a movement such that they amend an ongoing action. Submovements are associated with activity of the basal ganglia, implying a role for the structures in error correction. In parallel, the basal ganglia are linked to the generation and control of force amplitude, change, and duration. Here, we tested whether activity in human basal ganglia is associated with submovements generally, or was specific to a condition where the submovements only occurred in the face of unexpected proprioceptive error. Submovements were induced by introducing unexpected and variable viscous loads (augmenting the need for trial-specific grip forces) or by reducing target size (augmenting the need for visually guided on-line control) in a one-dimensional target-capture task. In both cases, subjects compensated for the increased task difficulty by generating corrective submovements, which were closely matched in frequency and type. Activity in the internal segment of the globus pallidus and subthalamic nucleus correlated strongly with the number of submovements during the viscous challenge but not with the target challenge. The effects could not be explained by kinematic differences, i.e., movement amplitude or average number of submovements. The results support a specific role for the basal ganglia in error correction under conditions of variable load where there is a need for the dynamic control of force within an ongoing movement.

Human movement onset detection from isometric force and torque measurements: a supervised pattern recognition approach

OBJECTIVE

Recent research has successfully introduced the application of robotics and mechatronics to functional assessment and motor therapy. Measurements of movement initiation in isometric conditions are widely used in clinical rehabilitation and their importance in functional assessment has been demonstrated for specific parts of the human body. The determination of the voluntary movement initiation time, also referred to as onset time, represents a challenging issue since the time window characterizing the movement onset is of particular relevance for the understanding of recovery mechanisms after a neurological damage. Establishing it manually as well as a troublesome task may also introduce oversight errors and loss of information.

METHODS

The most commonly used methods for automatic onset time detection compare the raw signal, or some extracted measures such as its derivatives (i.e., velocity and acceleration) with a chosen threshold. However, they suffer from high variability and systematic errors because of the weakness of the signal, the abnormality of response profiles as well as the variability of movement initiation times among patients. In this paper, we introduce a technique to optimise onset detection according to each input signal. It is based on a classification system that enables us to establish which deterministic method provides the most accurate onset time on the basis of information directly derived from the raw signal.

RESULTS

The approach was tested on annotated force and torque datasets. Each dataset is constituted by 768 signals acquired from eight anatomical districts in 96 patients who carried out six tasks related to common daily activities. The results show that the proposed technique improves not only on the performance achieved by each of the deterministic methods, but also on that attained by a group of clinical experts.

CONCLUSIONS

The paper describes a classification system detecting the voluntary movement initiation time and adaptable to different signals. By using a set of features directly derived from raw data, we obtained promising results. Furthermore, although the technique has been developed within the scope of isometric force and torque signal analysis, it can be applied to other detection problems where several simple detectors are available.

Basal ganglia contribution to the initiation of corrective submovements

We investigated the neural processes, with a focus on subcortical circuits, which govern corrective submovements in visually targeted action. During event-related fMRI, subjects moved a cursor to capture targets presented at varying movement amplitudes. Movements were performed in a rehearsed null and a novel viscous (25% random trials) torque field. Movement error feedback was provided after each trial. The viscous field invoked a significantly larger error at the end of the primary movement. Subjects compensated by producing more corrections than they had in the null condition. Corrective submovements were appropriately scaled such that terminal error was similar between the two conditions. Parametric analysis identified two regions where the BOLD signal correlated with the number of submovements per trial: a cerebellar region similar to the one noted in the task contrast and the contralateral dorsal putamen. A separate parametric analysis identified brain regions where activity correlated with movement amplitude. This identified the same cerebellar region as above, bilateral parietal cortex, and left motor and premotor cortex. Our data indicate that the basal ganglia and cerebellum play complementary roles in regulating ongoing actions when precise updating is required. The basal ganglia have a key role in contextually-based motor decision-making, i.e. for deciding if and when to correct a given movement by initiating corrective submovements, and the cerebellum is more generally involved in amplifying and refining the command signals for movements of different amplitudes.

Differential recruitment of anterior intraparietal sulcus and superior parietal lobule during visually guided grasping revealed by electrical neuroimaging

Dorsal parietal cortex is required for visually guided prehension. Transcranial magnetic stimulation to either the anterior intraparietal sulcus (aIPS) or superior parietal lobule (SPL) disrupts on-line adaptive adjustments of grasp when objects are perturbed. We used high-density electroencephalography during grasping to determine the relative timing of these two areas and to test whether the temporal contribution of each site would change when the task goal was perturbed. During object grasping with the right-hand, two distinct evoked responses were present over the 50-100 and 100-200 ms periods after movement onset. Distributed linear source estimation of these scalp potentials localized left lateralized sources, first in the aIPS and then the SPL. The duration of the response from the aIPS area was longer when there was an object perturbation. Initiation of a corrective movement coincided with activation in SPL. These data support a two-stage process: the integration of target goal and an emerging action plan within aIPS and subsequent on-line adjustments within SPL.

Dopamine replacement therapy does not restore the ability of Parkinsonian patients to make rapid adjustments in motor strategies according to changing sensorimotor contexts

The ability of dopamine replacement to restore rapid motor adjustments in Parkinson's disease (PD) was investigated. Medicated and non-medicated patients performed finger-to-nose movements while simultaneously bending the trunk forward, without vision. Trunk motion was blocked unexpectedly, necessitating rapid adjustments in arm trajectories. Patients exhibited irregular hand paths, plateaus in hand velocity, and prolonged movement times, which were significantly greater in perturbed trials. Medication improved kinematics but perturbation-induced disturbances persisted and did not approximate the levels of non-perturbed trials nor those of controls. Dopaminergic replenishment in PD may therefore have limited restorative benefits for rapid context-specific motor control.

Deciding when and how to correct a movement: discrete submovements as a decision making process

Rapid reaching movements of human and non-human primates are often characterized by irregular multi-peaked velocity profiles. How to interpret these irregularities is still under debate. While some reports assert that these irregularities are the result of a continuous controller interacting with the environment, we and others hold that the velocity irregularities are evidence for a controller that produces discrete movement corrections. Here we analyze rapid pronation/supination wrist movements in monkey during a 1D step-tracking task, where visual perturbations of the target were randomly introduced at movement onset. We use our recently introduced algorithm (Fishbach et al. in Exp Brain Res 164:442-457, 2005) to decompose an irregular movement into a primary movement and one or more discrete, corrective submovements. We first show that the visual perturbation has almost no effect on primary movements. In contrast, this perturbation influences the type and the extent of the corrective submovements that often follow primary movements. Secondly, we show that the highly variable timing of overlapping submovements does not depend directly on the visual perturbation but rather on an estimate of the movement error and on the movement's extent-to-go at the time of correction initiation. These results are consistent with a forward-model based intermittent controller with a non-linearity that depends both on a prediction of the magnitude and direction of the movement's error and on its variance. Corrections are initiated only when the predicted error is statistically significant. A simple abstract model that implements these principles accounts for the type and timing of the corrections observed in our data.

Virtual lesions of the anterior intraparietal area disrupt goal-dependent on-line adjustments of grasp

Adaptive motor behavior requires efficient error detection and correction. The posterior parietal cortex is critical for on-line control of reach-to-grasp movements. Here we show a causal relationship between disruption of cortical activity within the anterior intraparietal sulcus (aIPS) by transcranial magnetic stimulation (TMS) and disruption of goal-directed prehensile actions (either grip size or forearm rotation, depending on the task goal, with reaching preserved in either case). Deficits were elicited by applying TMS within 65 ms after object perturbation, which attributes a rapid control process on the basis of visual feedback to aIPS. No aperture deficits were produced when TMS was applied to a more caudal region within the intraparietal sulcus, to the parieto-occipital complex (putative V6, V6A) or to the hand area of primary motor cortex. We contend that aIPS is critical for dynamic error detection during goal-dependent reach-to-grasp action that is visually guided.