Coordination of prehensile forces during precision grip in Huntington's disease

Reliability of spatiotemporal gait outcome measures in Huntington's disease

Gait impairments are very important in Huntington's disease (HD), because loss of independence in gait is an important predictor of nursing home placement. Given this importance, it is imperative to test reliable and sensitive outcome measures that can be tested easily in various clinical environments. Here, we examined the test-retest reliability of gait outcome measures using the GAITRite instrumented carpet. We tested 12 subjects with HD and 12 age-matched controls in two separate sessions. At each session, subjects walked across the GAITRite carpet at a comfortable speed. We used the intraclass correlation coefficient (ICC) and coefficient of variation (CoV) to measure test-retest reliability. Reliability was very high for all outcome measures (velocity, cycle time, stride length, cadence, and base of support), as seen by high ICC scores (0.86 to 0.95) and low CoV scores (0.042-0.102). In addition, the performance across the two subject groups was very different, indicating that the GAITRite is sensitive enough to distinguish between populations. Given that the GAITRite is a relatively inexpensive and portable piece of equipment, it can be used in a wide variety of clinical settings and clinical trials. Our data on high test-retest reliability and sensitivity extends the utility of the GAITRite to the HD population.

Effect of object transport on grasp coordination in multiple system atrophy

We examined the effects of the parkinsonian variant of multiple-system atrophy (MSA-P) on grasp and forward transport and release of an object. Twelve patients with MSA-P and 10 age-matched control subjects performed the task with each of three object weights (200, 400, 800 gm). Subjects moved at a self-selected pace using a precision grip. The grip (normal) and load (tangential) forces and the object position were recorded. Results indicate subjects with MSA-P have temporal and force coordination deficits. Temporal delays were seen in all subjects with MSA-P, leading to prolonged overall movement times compared to control subjects. These delays occurred throughout the task, with significantly longer transport phases and delays releasing the object. Despite demonstrating an appropriate anticipatory scaling of forces, with increasing grip and load forces for heavier weights, force coordination was compromised in subjects with MSA-P. These subjects generated significant negative load forces prior to transporting the object. In addition, during the transport phase, subjects with MSA-P generated highly variable grip forces. Overall, the results indicate that subjects with MSA-P demonstrate bradykinesia and difficulty coordinating components of an object transport task.

Early Huntington's disease affects movements in transformed sensorimotor mappings

This study examined the effect of transformed visual feedback on movement control in Huntington's disease (HD). Patients in the early stages of HD and controls performed aiming movements towards peripheral targets on a digitizing tablet and emphasizing precision. In a baseline condition, HD patients were slower but showed few precision problems in aiming. When visual feedback was inverted in both vertical and horizontal axes, patients showed problems in initial and terminal phases of movement where feedback is most critical. When visual feedback was inverted along a single axis as in a mirror-inversion, HD patients showed large deviations and over-corrections before adaptation. Adaptation was similar in both groups. These results suggest that HD impairs on-line error correction in novel movements.

Sensorimotor mapping affects movement correction deficits in early Huntington's disease

Huntington's disease (HD) is associated with early voluntary movement problems linked to striatal dysfunction. In pointing movements, HD increases the irregularity of the terminal part of movements, suggesting a dysfunction in error feedback control. We tested this hypothesis in movements requiring continuous feedback control. Patients in the early stages of HD and controls traced as fast and accurately as possible circles within a 5-mm annulus on a digitizing tablet when visual feedback of the hand and the circle was direct or indirect (through a monitor). Patients deviated more often from the annulus and showed larger corrections toward the circle than controls when using indirect visual feedback but not with direct visual feedback. When velocity requirements were removed, patients showed little change in these control problems. These results suggest that HD does not affect error feedback control in all movements and that the striatal contribution to voluntary movement is sensitive to sensorimotor mapping.

Grip force behavior in Gilles de la Tourette syndrome

We analyzed predictive and reactive grip force behavior in 15 patients with Gilles de la Tourette syndrome (GTS) and 15 sex- and age-matched healthy control subjects. Nine patients were without medication; six patients were on medication. In a first experiment, participants lifted and held instrumented objects of different weight. In a second experiment, participants performed vertical point-to-point and continuous arm movements at different frequencies with a hand-held object. In a third experiment, preparatory and reactive grip force responses to sudden load perturbations were analyzed when a weight was dropped into a hand-held cup either by the subject or unexpectedly by the experimenter. Compared to the healthy subjects, GTS patients had increased grip forces relative to the load force in all tasks. Despite this finding, they adjusted the grip force to changes in load force (due to either a change in the mass lifted or accelerating the mass during continuous movements) in the same way as healthy subjects. The temporal coupling between grip and load force profiles was also similar in patients and healthy controls, and they displayed normal anticipation of impact forces when they dropped a weight into a hand-held cup. We found no significant effect of medication on the performance of GTS patients, regardless of the task performed. These results are consistent with deficient sensory-motor processing in Gilles de la Tourette syndrome.

Preserved and impaired aspects of predictive grip force control in cerebellar patients

OBJECTIVE

To analyze preserved and impaired aspects of feedforward grip force control during cyclic arm movements with a hand-held object after cerebellar damage.

METHODS

We tested eight subjects with unilateral or bilateral cerebellar pathologies and eight healthy control subjects. Participants performed cyclic vertical arm movements with a hand held instrumented object at three different speeds.

RESULTS

Compared to controls, patients excerted increased grip forces. The minimum force ratio between grip force and load force was constant across all movement frequencies, suggesting that patients anticipated speed-related changes in load magnitudes by adjusting the grip force. Thus the scaling of grip force level to self-generated load magnitudes was preserved. The coupling between grip and load profiles was assessed by cross correlation analysis. Patients exhibited significantly decreased maximum coefficients of cross correlation implicating impaired anticipation of inertial load fluctuations. However feedforward control could be preserved, as obvious from zero time lags of the maximum cross correlation coefficient.

CONCLUSIONS

Our findings suggest that cerebellar lesions affect the processing of predictive grip force modulation in anticipation of inertial loads. Our results add further evidence to the theoretical concept that the cerebellum implements internal feedforward models. However, preserved functions may indicate compensatory mechanisms or extra-cerebellar aspects of grip and load force regulation.

SIGNIFICANCE

The observed dissociation of performance deficits may have direct clinical implication and may guide the development of individual therapeutic strategies for patients with cerebellar disorders.

Chronology of behavioral symptoms and neuropathological sequela in R6/2 Huntington's disease transgenic mice

Genetic murine models play an important role in the study of human neurological disorders by providing accurate and experimentally accessible systems to study pathogenesis and to test potential therapeutic treatments. One of the most widely employed models of Huntington's disease (HD) is the R6/2 transgenic mouse. To characterize this model further, we have performed behavioral and neuropathological analyses that provide a foundation for the use of R6/2 mice in preclinical therapeutic trials. Behavioral analyses of the R6/2 mouse reveal age-related impairments in dystonic movements, motor performance, grip strength, and body weight that progressively worsen until death. Significant neuropathological sequela, identified as increasing marked reductions in brain weight, are present from 30 days, whereas decreased brain volume is present from 60 days and decreased neostriatal volume and striatal neuron area, with a concomitant reduction in striatal neuron number, are present at 90 days of age. Huntingtin-positive aggregates are present at postnatal day 1 and increase in number and size with age. Our findings suggest that the R6/2 HD model exhibits a progressive HD-like behavioral and neuropathological phenotype that more closely corresponds to human HD than previously believed, providing further assurance that the R6/2 mouse is an appropriate model for testing potential therapies for HD.

Grip force behavior during object manipulation in neurological disorders: Toward an objective evaluation of manual performance deficits

The control of prehensile finger forces is an essential feature of skilled manual performance. The basic aspects of healthy grip force behavior have been well documented. In healthy subjects, grip force is precisely adjusted to the mechanical object properties. Grip force is always slightly higher than the minimum necessary to prevent the object from slipping. When we move a hand-held object, grip force is modulated in parallel with movements-induced load fluctuations without an obvious delay. The absence of a temporal delay between grip and load force profiles suggests that the central nervous system is able to predict the load variations before the intended manipulation and consequently regulates grip force in anticipation. Feedback from the grasping fingertips is used to adjust the level of applied fingertip force efficiently to the actual loading requirements. Pathologic grip force control affects the efficiency of produced force and the precision of the temporal coupling between grip and load force profiles. Here, we review the characteristics of pathologic grip force behavior in various neurological disorders. Detailed examination of grip force control is simple and well suited for the objective evaluation of impaired motor function of the hand and its rehabilitation.

Objective assessment of motor slowness in Huntington's disease: clinical correlates and 2-year follow-up

Functional disability of patients with Huntington's disease (HD) is determined by impairment of voluntary motor function rather than the presence of chorea. However, only few attempts have been made to quantify this motor impairment. By using a simple reaction time paradigm, we measured the time needed for movement initiation (akinesia) and execution (bradykinesia) in 76 HD patients and 127 controls. Akinesia and bradykinesia were already evident in early stages and increased linearly with increasing disease stage. Quantified motor slowness correlated with clinical impairment of voluntary movements but also with cognitive impairment and medication use. In patients without severe cognitive impairment, quantified motor slowness reflected clinical motor impairment more purely. During 1.9 years follow-up (range, 0.8-3.8 years), quantified akinesia and bradykinesia progressed concomitantly with progression of clinical impairment of voluntary movements, cognition, and functional capacity. However, rate of change in motor slowness did not discriminate between patients whose disease stage remained stable and those whose disease stage progressed. We conclude that the reaction time paradigm may be used to quantify akinesia and bradykinesia in HD, at least in patients without severe cognitive impairment. Although reaction and movement times increased in time, these measures failed to detect functionally important changes during our follow-up period.

Grip force abnormalities in de novo Parkinson's disease

In recent years it has been shown that a variety of movement disorders are associated with abnormalities of the fine motor control of the hand. In Parkinson's disease (PD), these changes consist of a slowing of the rate of grip force development and the use of abnormally large grip forces both during lifting and static holding of an object. It has been suggested, however, that these changes are a direct effect of the patient's levodopa medication or associated with levodopa induced dyskinesias. Accordingly, we examined the performance of de novo Parkinson patients in a precision lifting task. All patients (n = 6) were newly diagnosed and showed rigidity, bradykinesia, or both, but were unaffected by tremor or dyskinesia. None of the patients had received antiparkinson medication. Grip force was abnormally high in both the lifting and hold phases. This exaggeration was equal in magnitude to that observed previously in medicated patients. Thus we conclude that the abnormalities in grip force observed here are intrinsic features of PD and not the result of dopamine medication or its side effects.

Coordination of fingertip forces during precision grasping in multiple system atrophy

While the pathology and autonomic nervous system components of multiple system atrophy (MSA) have been well described, little is known about the associated motor dysfunction. One prominent feature of MSA is parkinsonism, although ataxias and pyramidal tract signs are frequently present. To investigate the nature of motor deficits in MSA, a natural grip-lift movement requiring a precision grasp was used to examine force coordination. Subjects were asked to grasp an instrumented object using the fingertips of the thumb and index finger and lift it 10 cm above the table surface. Subjects with MSA demonstrated a prolonged duration between object contact and initiation of the lifting drive that increased with the weight of the object. During this period these subjects produced large grasping forces generating a significant portion of the eventual grip force employed to hold the object. In contrast, control subjects generated grip and load forces in parallel after establishing contact with the object. Therefore, subjects with MSA showed a disrupted performance on both the sequential (grasp, then lift) and simultaneous (grip and load force development) portions of this task. Only after initiation of the vertical lifting drive did subjects with MSA generate forces in a similar manner to control subjects. These findings demonstrate that subjects with MSA exhibit a disrupted coordination of grasp and could suggest a general deficit in motor control resulting from multi-focal neural degeneration.

Manual transport in Parkinson's disease

We analyze hand dexterity in Parkinson's disease patients (PD) and control subjects using a natural manual transport task (moving an object from one place to another). Eight PD patients and 10 control subjects carried out the task repeatedly at maximum speed both in off and on medicated status. The movement parameters and the grip and load forces were recorded. Using the force and velocity signals, 10 subsequent phases of the transport movement were defined and their durations were measured. The difference between the control group and the test group in off and on was established statistically using non-parametric methods. There was slowed reaching and a striking disturbance of establishing the precision grip in PD. The transport capabilities were impaired differentially. Although acceleration and reaching sufficient height of the lift were disturbed in PD subjects, transport of the object toward the target position was almost normal. A partial disturbance was observed when cancelling the grip. Dopaminergic medication improved only specific hand skills, especially establishment of the precision grip and one of the four transport phases. A long movement path was more sensitive for movement disturbance in Parkinson's disease than a short one.

Grip force control during object manipulation in cerebral stroke

OBJECTIVE

To analyze impairments of manipulative grip force control in patients with chronic cerebral stroke and relate deficits to more elementary aspects of force and grip control.

METHODS

Nineteen chronic stroke patients with fine motor deficits after unilateral cerebral lesions were examined when performing 3 manipulative tasks consisting of stationary holding, transport, and vertical cyclic movements of an instrumented object. Technical sensors measured the grip force used to stabilize the object in the hand and the object accelerations, from which the dynamic loads were calculated.

RESULTS

Many patients produced exaggerated grip forces with their affected hand in all types of manipulations. The amount of finger displacement in a grip perturbation task emerged as a highly sensitive measure for predicting the force increases. Measures of grip strength and maximum speed of force changes could not account for the impairments with comparable accuracy. In addition to force economy, the precision of the coupling between grip and load forces was impaired. However, no temporal delays were typically observed between the grip and load force profiles during cyclic movements.

CONCLUSIONS

Impaired sensibility and sensorimotor processing, evident by delayed reactions in the perturbation task, lead to an excessive increase of the safety margin between the actual grip force and the minimum force necessary to prevent object slipping. In addition to grip force scaling, cortical sensorimotor areas are responsible for smoothly and precisely adjusting grip forces to loads according to predictions about movement-induced loads and sensory experiences. However, the basic feedforward mechanism of grip force control by internal models appears to be preserved, and thus may not be a cortical but rather a subcortical or cerebellar function, as has been suggested previously.

Effectiveness of physiotherapy, occupational therapy, and speech pathology for people with Huntington's disease: a systematic review

This review provides a summary of the current literature examining the outcomes of physiotherapy, occupational therapy, and speech pathology interventions for people with Huntington's disease. The literature was retrieved via a systematic search using a combination of key words that included Huntington's disease, physiotherapy, occupational therapy, and speech pathology. The electronic databases for Medline, Embase, CINAHL, Cochrane Controlled Trials Register, and PEDro were searched up to May 2002. Articles meeting the review criteria were graded for study type and rated for quality using checklists to assess study validity and methodology. The majority of articles that examined therapy outcomes for people with Huntington's disease were derived from observational studies of low methodological quality. A low level of evidence exists to support the use of physiotherapy for addressing impairments of balance, muscle strength, and flexibility. There was a small amount of evidence to support the use of speech pathology for the management of eating and swallowing disorders. The current evidence is insufficient to make strong recommendations regarding the usefulness of physiotherapy, occupational therapy, or speech pathology for people with Huntington's disease. There is further need for therapy outcomes research in Huntington's disease so that clinicians may use evidence-based practice to assist clinical decision making.

Sensation of effort is altered in Huntington's disease

In this study, we investigated sensation of effort in Huntington disease (HD). We tested the hypothesis that the basal ganglia are involved in processing effort sensation. The experimental paradigm consisted in a contralateral matching procedure where normal subjects (N=6) and HD patients (N=6) were required to lift a reference weight with their non-dominant index, and then compare the target-weight with variable weights lifted by the dominant index. Two kinds of sequences were administered: (1) increasing, where the first weight was lighter than the reference weight and progressively increased in 20g steps, (2) decreasing, where trials started with a heavier weight and progressively decreased. We calculated the discrimination threshold (DT) across sequences as the weight for which the subject's response changed sign. The difference between the higher and the lower threshold was defined as "uncertain area". We predicted that controls should overestimate the reference weight lifted by their non-dominant hand because the same effort produces more force when applied to stronger muscles. If the basal ganglia mediates sensation of effort, patients' capability to discriminate weights should be degraded. As expected, normal subjects overestimated the reference weight lifted by their non-dominant index and showed a restricted uncertain area, thus, indicating that were able to discriminate minimal differences in generated forces. By contrast, patients with HD underestimated the reference weight lifted by their non-dominant hand and showed a broad uncertain area, thus, demonstrating that they could detect only important differences in the matched efforts. These results suggest that effort sensation critically involves the basal ganglia. In normal conditions, in parallel with the efferent command of force, an efferent copy reflecting the magnitude of the voluntary motor command is transmitted to sensory centres. This signal and/or the integration of sensory feedback which generates what is experienced as the sense of effort, would be altered in HD.

Movement control of manipulative tasks in patients with Gilles de la Tourette syndrome

When a hand-held object is moved, grip and load force are accurately coordinated for establishing grasp stability. In the present work, the question was raised whether patients with Gilles de la Tourette syndrome (TS), who show tic-like movements, are impaired in grip-load force control when executing a manipulative task. To this end, we assessed force regulation during action patterns that required rhythmical unimanual or bimanual (iso-directional/anti-directional) movements. Results showed that the profile of grip-load force ratio was characterized by maxima and minima that were realized at upward and downward hand positions, respectively. TS patients showed increased force ratios during unimanual and bimanual movements, compared with control subjects, indicative of an inaccurate specification of the precision grip. Functional imaging data complemented the behavioural results and revealed that secondary motor areas showed no (or greatly reduced) activation in TS patients when executing the movement tasks as compared with baseline conditions. This indicates that the metabolic level in the secondary motor areas was equal during rest and task performance. At the neuronal level, this observation suggests that these cortical areas were continuously involved in movement preparation. Based on these data, we conclude that the ongoing activation of secondary motor areas may be explained by the TS patients' involuntary urges to move. Accordingly, interference will prevent an accurate planning of voluntary behaviour. Together, these findings reveal modulations in movement organization in patients with TS and exemplify degrading consequences for manual function.

Grip force scaling and sequencing of events during a manipulative task in Huntington's disease

The aim of the study was to investigate force regulation and sequencing of events in Huntington's disease (HD) patients when performing a drawer opening task using the precision grip. Results revealed that HD patients used excessive grip force levels that were unrelated to the actual task demands. Also, they demonstrated a higher grip force value at load force onset in addition to an increased delay between initiation of grip force and load (pulling) force. These data indicate a deficit in the coordinated activation of both forces due to HD. Furthermore, the patients showed bradykinesia along with a prolonged interval between the movement phases underlying the task, denoting an impairment in encoding serially ordered events. Together, these results illustrate the deteriorating effect of striatal pathology on manual function. Accordingly, an amended control of grasping forces and serial encoding of movement-related events due to HD are likely to affect the proficiency of common manipulative skills.

Altered movement trajectories and force control during object transport in Huntington's disease

Individuals with Huntington's Disease (HD) have difficulty grasping and transporting objects, however, the extent to which specific impairments affect their performance is unknown. The present study examined the kinematics and force coordination during transport of an object in 12 subjects with HD and 12 age-matched controls. Subjects grasped an object between their thumb and index finger, transported it 25 cm forward, replaced and released it while their fingertip forces and the object's position were recorded. Five trials were performed with each of three weights (200 g, 400 g, and 800 g). While bradykinesia was evident in subjects with HD, this slowness was not consistently observed in all phases of the movement. The slowness of movement seen during the task appears to be due to impairments in sequencing and the movement strategies selected by the subjects. Compared to control subjects, subjects with HD produced highly curvilinear hand paths and more variable grip forces that were dependent on the weight of the object. Isometric force development and movement speed during transport were unaffected by the disease. The results suggest that prolonged task durations in subjects with HD are not necessarily due to slowness of movement, per se. These findings have clinical implications for understanding the task-specific nature of movement impairments in HD and developing effective intervention strategies.