Reliance on advance information and movement sequencing in Huntington's disease

Frequency of depression in Huntington's disease: A systematic review and meta-analysis

BackgroundHuntington's disease (HD) is a hereditary neurodegenerative disease characterized by a combination of motor, cognitive, and mental health issues, with depression being the most common. Despite its importance, the relationship between depression and disease progression is still debatable.ObjectiveThe primary objective of this study was to examine the frequency of depression across different disease stages in individuals with HD. We also explored the associations between depression and other HD-related factors.MethodsThis systematic review comprehensively searched MEDLINE, APA PsycINFO, and Embase databases for studies on depression in individuals with HD. Pooled depression frequencies were calculated for premanifest and manifest HD. Depression was analyzed based on HD functional stages and diagnostic tools, alongside reviewing its association with various HD factors.ResultsWe assessed 6523 records and included 104 studies. Our meta-analyses revealed that the overall frequency of depression was higher in manifest HD compared to premanifest HD (0.38 vs. 0.23). However, the progression of depression did not follow a consistent pattern, with peaks occurring in earlier rather than later stages. Additionally, the frequency of depression was lower in studies using diagnostic criteria compared to those using clinical scales (0.25 vs. 0.42).ConclusionsOur findings showed that the rate of depression is high in HD and varies depending on the disease stage and the criteria used. This emphasizes the necessity for tailored and unified diagnostic criteria for depression in HD.

HD-DRUM, a Tablet-Based Drumming Training App Intervention for People With Huntington Disease: App Development Study

BACKGROUND

Huntington disease (HD) is a neurodegenerative condition that leads to progressive loss of cognitive-executive and motor functions, largely due to basal ganglia (BG) atrophy. Currently, there are no therapeutic interventions tailored to address executive and motor dysfunction in people with HD. Music-based interventions may aid executive abilities by compensating for impaired BG-reliant timing and rhythm generation using external rhythmic beats. Here, we applied an integrated knowledge translation (IKT) framework to co-design a tablet-based rhythmic drumming training app (HD-DRUM) to stimulate executive and motor abilities in people with HD.

OBJECTIVE

The primary aim was to develop the HD-DRUM app for at-home use that addressed the accessibility needs of people with HD and allowed for the quantification of performance improvements and adherence for controlled clinical evaluation.

METHODS

The IKT framework was applied to iteratively refine the design of HD-DRUM. This process involved 3 phases of knowledge user engagement and co-design: a web-based survey of people with HD (n=29) to inform about their accessibility needs, usability testing of tablet-based touch screens as hardware solutions, and usability testing of the design and build of HD-DRUM to meet the identified accessibility needs of people affected by HD and their clinicians (n=12).

RESULTS

The survey identified accessibility problems due to cognitive and motor control impairments such as difficulties in finding and navigating through information and using PC keyboards and mouses to interact with apps. Tablet-based touch screens were identified as feasible and accessible solutions for app delivery. Key elements to ensure that the app design and build met the needs of people with HD were identified and implemented. These included the facilitation of intuitive navigation through the app using large and visually distinctive buttons; the use of audio and visual cues as training guides; and gamification, positive feedback, and drumming to background music as a means to increase motivation and engagement. The co-design development process resulted in the proof-of-concept HD-DRUM app that is described here according to the Template for Intervention Description and Replication checklist. HD-DRUM can be used at home, allowing the quantification of performance improvements and adherence for clinical evaluation, matching of training difficulty to users' performance levels using gamification, and future scale-up to reach a wide range of interested users.

CONCLUSIONS

Applying an IKT-based co-design framework involving knowledge user engagement allowed for the iterative refinement of the design and build of the tablet-based HD-DRUM app intervention, with the aim of stimulating BG-reliant cognitive and motor functions. Mapping the intervention against the Template for Intervention Description and Replication framework to describe complex interventions allowed for the detailed description of the HD-DRUM intervention and identification of areas that required refinement before finalizing the intervention protocol.

Emerging concepts on bradykinesia in non-parkinsonian conditions

BACKGROUND AND PURPOSE

Bradykinesia is one of the cardinal motor symptoms of Parkinson's disease. However, clinical and experimental studies indicate that bradykinesia may also be observed in various neurological diseases not primarily characterized by parkinsonism. These conditions include hyperkinetic movement disorders, such as dystonia, chorea, and essential tremor. Bradykinesia may also be observed in patients with neurological conditions that are not seen as "movement disorders," including those characterized by the involvement of the cerebellum and corticospinal system, dementia, multiple sclerosis, and psychiatric disorders.

METHODS

We reviewed clinical reports and experimental studies on bradykinesia in non-parkinsonian conditions and discussed the major findings.

RESULTS

Bradykinesia is a common motor abnormality in non-parkinsonian conditions. From a pathophysiological standpoint, bradykinesia in neurological conditions not primarily characterized by parkinsonism may be explained by brain network dysfunction.

CONCLUSION

In addition to the pathophysiological implications, the present paper highlights important terminological issues and the need for a new, more accurate, and more widely used definition of bradykinesia in the context of movement disorders and other neurological conditions.

Quantifying Postural Control in Premanifest and Manifest Huntington Disease Using Wearable Sensors

Background. Impairments in postural control in Huntington disease (HD) have important consequences for daily functioning. This observational study systematically examined baseline postural control and the effect of sensory attenuation and sensory enhancement on postural control across the spectrum of HD. Methods. Participants (n = 39) included healthy controls and individuals in premanifest (pHD) and manifest stages (mHD) of HD. Using wearable sensors, postural control was assessed according to (1) postural set (sit vs stand), (2) sensory attenuation using clinical test of sensory integration, and (3) sensory enhancement with gaze fixation. Outcomes included sway smoothness, amplitude, and frequency. Results. Based on postural set, pHD reduced postural sway in sitting relative to standing, whereas mHD had pronounced sway in standing and sitting, highlighting a baseline postural deficit. During sensory attenuation, postural control in pHD deteriorated relative to controls when proprioceptive demands were high (eyes closed on foam), whereas mHD had significant deterioration of postural control when proprioception was attenuated (eyes open and closed on foam). Finally, gaze fixation improved sway smoothness, amplitude, and frequency in pHD; however, no benefit was observed in mHD. Conclusions. Systematic examination of postural control revealed a fundamental postural deficit in mHD, which further deteriorates when proprioception is challenged. Meanwhile, postural deficits in pHD are detectable when proprioceptive challenge is high. Sensory enhancing strategies using gaze fixation to benefit posture may be useful when introduced well before motor diagnosis. These findings encourage further examination of wearable sensors as part of routine clinical assessments in HD.

Implicit learning impairment identified via predictive saccades in Huntington's disease correlates with extended cortico-striatal atrophy

The ability to anticipate events and execute motor commands prior to a sensory event is an essential capability for human's everyday life. This implicitly learned anticipatory behavior depends on the past performance of repeated sensorimotor interactions timed with external cues. This kind of predictive behavior has been shown to be compromised in neurological disorders such as Huntington disease (HD), in which neural atrophy includes key cortical and basal ganglia regions. To investigate the neural basis of the anticipatory behavioral deficits in HD we used a predictive-saccade paradigm that requires predictive control to generate saccades in a metronomic temporal pattern. This is ideal because the integrity of the oculomotor network that includes the striatum and prefrontal, parietal, occipital and temporal cortices can be analyzed using structural MRI. Our results showed that the HD patients had severe predictive saccade deficits (i.e., an inability to reduce saccade reaction time in predictive condition), which are accentuated in patients with more severe motor deterioration. Structural imaging analyses revealed that these anticipatory deficits correlated with grey-matter atrophy in frontal, parietal-occipital and striatal regions. These findings indicate that the predictive saccade control deficits in HD are related to an extended cortico-striatal atrophy. This suggests that eye movement measurement could be a reliable marker of the progression of cognitive deficits in HD.

Automated Assessment of Movement Impairment in Huntington's Disease

Quantitative assessment of movement impairment in Huntington's disease (HD) is essential to monitoring of disease progression. This paper aimed to develop and validate a novel low cost, objective automated system for the evaluation of upper limb movement impairment in HD in order to eliminate the inconsistency of the assessor and offer a more sensitive, continuous assessment scale. Patients with genetically confirmed HD and healthy controls were recruited to this observational study. Demographic data, including age (years), gender, and unified HD rating scale total motor score (UHDRS-TMS), were recorded. For the purposes of this paper, a modified upper limb motor impairment score (mULMS) was generated from the UHDRS-TMS. All participants completed a brief, standardized clinical assessment of upper limb dexterity while wearing a tri-axial accelerometer on each wrist and on the sternum. The captured acceleration data were used to develop an automatic classification system for discriminating between healthy and HD participants and to automatically generate a continuous movement impairment score (MIS) that reflected the degree of the movement impairment. Data from 48 healthy and 44 HD participants was used to validate the developed system, which achieved 98.78% accuracy in discriminating between healthy and HD participants. The Pearson correlation coefficient between the automatic MIS and the clinician rated mULMS was 0.77 with a p-value < 0.01. The approach presented in this paper demonstrates the possibility of an automated objective, consistent, and sensitive assessment of the HD movement impairment.

Of rodents and men: understanding the emergence of motor and cognitive symptoms in Huntington disease

Arguably, one of the most important milestones in Huntington disease research since the discovery of the gene responsible has been the generation of different genetic animal models. Although clinical reports have shown evidence of progressive cognitive impairments in gene carriers before motor symptoms are diagnosed, such symptoms have been much less obvious in animal models. In this review, we summarize the three main classes of animal models for Huntington disease and describe some relevant translational assays for behavioural deficits evaluation. Finally, we argue that a good knowledge of the emergence of motor and cognitive symptoms in mice and rat models is indispensable for the selection of endpoint measures in early preclinical drug screening studies.

Quantitative Gait Analysis in Patients with Huntington's Disease

Objective

Gait disturbance is the main factor contributing to a negative impact on quality of life in patients with Huntington’s disease (HD). Understanding gait features in patients with HD is essential for planning a successful gait strategy. The aim of this study was to investigate temporospatial gait parameters in patients with HD compared with healthy controls.

Methods

We investigated 7 patients with HD. Diagnosis was confirmed by genetic analysis, and patients were evaluated with the Unified Huntington’s Disease Rating Scale (UHDRS). Gait features were assessed with a gait analyzer. We compared the results of patients with HD to those of 7 age- and sex-matched normal controls.

Results

Step length and stride length were decreased and base of support was increased in the HD group compared to the control group. In addition, coefficients of variability for step and stride length were increased in the HD group. The HD group showed slower walking velocity, an increased stance/swing phase in the gait cycle and a decreased proportion of single support time compared to the control group. Cadence did not differ significantly between groups. Among the UHDRS subscores, total motor score and total behavior score were positively correlated with step length, and total behavior score was positively correlated with walking velocity in patients with HD.

Conclusion

Increased variability in step and stride length, slower walking velocity, increased stance phase, and decreased swing phase and single support time with preserved cadence suggest that HD gait patterns are slow, ataxic and ineffective. This study suggests that quantitative gait analysis is needed to assess gait problems in HD.

Characterising Upper Limb Movements in Huntington's Disease and the Impact of Restricted Visual Cues

BACKGROUND

Voluntary motor deficits are a common feature in Huntington's disease (HD), characterised by movement slowing and performance inaccuracies. This deficit may be exacerbated when visual cues are restricted.

OBJECTIVE

To characterize the upper limb motor profile in HD with various levels of difficulty, with and without visual targets.

METHODS

Nine premanifest HD (pre-HD), nine early symptomatic HD (symp-HD) and nine matched controls completed a motor task incorporating Fitts' law, a model of human movement enabling the quantification of movement timing, via the manipulation of task difficulty (i.e., target size, and distance between targets). The task required participants to make reciprocal movements under cued and blind conditions. Dwell times (time stationary between movements), speed, accuracy and variability of movements were compared between groups.

RESULTS

Symp-HD showed significantly prolonged and less consistent movement times, compared with controls and pre-HD. Furthermore, movement planning and online control were significantly impaired in symp-HD, compared with controls and pre-HD, evidenced by prolonged dwell times and deceleration times. Speed and accuracy were comparable across groups, suggesting that group differences observed in movement time, variability, dwell time and deceleration time were evident over and above simple performance measures. The presence of cues resulted in greater movement time variability in symp-HD, compared with pre-HD and controls, suggesting that the deficit in movement consistency manifested only in response to targeted movements.

CONCLUSIONS

Collectively, these findings provide evidence of a deficiency in both motor planning, particularly in relation to movement timing and online control, which became exacerbated as a function of task difficulty during symp-HD stages. These variables may provide a more sensitive measure of motor dysfunction than speed and/or accuracy alone in symp-HD.

Intra-individual Variability in Prodromal Huntington Disease and Its Relationship to Genetic Burden

The current study sought to examine the utility of intra-individual variability (IIV) in distinguishing participants with prodromal Huntington disease (HD) from nongene-expanded controls. IIV across 15 neuropsychological tasks and within-task IIV using a self-paced timing task were compared as a single measure of processing speed (Symbol Digit Modalities Test [SDMT]) in 693 gene-expanded and 191 nongene-expanded participants from the PREDICT-HD study. After adjusting for depressive symptoms and motor functioning, individuals estimated to be closest to HD diagnosis displayed higher levels of across- and within-task variability when compared to controls and those prodromal HD participants far from disease onset (F ICV(3,877)=11.25; p<.0001; F PacedTiming(3,877)=22.89; p<.0001). When prodromal HD participants closest to HD diagnosis were compared to controls, Cohen's d effect sizes were larger in magnitude for the within-task variability measure, paced timing (-1.01), and the SDMT (-0.79) and paced tapping coefficient of variation (CV) (-0.79) compared to the measures of across-task variability [CV (0.55); intra-individual standard deviation (0.26)]. Across-task variability may be a sensitive marker of cognitive decline in individuals with prodromal HD approaching disease onset. However, individual neuropsychological tasks, including a measure of within-task variability, produced larger effect sizes than an index of across-task IIV in this sample.

Neurology of volition

Neurological disorders of volition may be characterized by deficits in willing and/or agency. When we move our bodies through space, it is the sense that we intended to move (willing) and that our actions were a consequence of this intention (self-agency) that gives us the sense of voluntariness and a general feeling of being "in control." While it is possible to have movements that share executive machinery ordinarily used for voluntary movement but lack a sense of voluntariness, such as psychogenic movement disorders, it is also possible to claim volition for presumed involuntary movements (early chorea) or even when no movement is produced (anosognosia). The study of such patients should enlighten traditional models of how the percepts of volition are generated in the brain with regard to movement. We discuss volition and its components as multi-leveled processes with feedforward and feedback information flow, and dependence on prior expectations as well as external and internal cues.

Cognitive functions and corticostriatal circuits: insights from Huntington's disease

The basic mechanisms of information processing by corticostriatal circuits are currently a matter of intense debate amongst cognitive scientists. Huntington's disease, an autosomal-dominant neurogenetic disorder characterized clinically by a triad of motor, cognitive, and affective disturbance, is associated with neuronal loss within corticostriatal circuits, and as such provides a valuable model for understanding the role of these circuits in normal behaviour, and their disruption in disease. We review findings from our studies of the breakdown of cognition in Huntington's disease, with a particular emphasis on executive functions and visual recognition memory. We show that Huntington's disease patients exhibit a neuropsychological profile that shows a discernible pattern of progression with advancing disease, and appears to result from a breakdown in the mechanisms of response selection. These findings are consistent with recent computational models that suggest that corticostriatal circuits compute the patterns of sensory input and response output which are of behavioural significance within a particular environmental context.

Utilisation of advance motor information is impaired in Friedreich ataxia

Friedreich ataxia (FRDA) is the most common of the genetically inherited ataxias. We sought to examine motor planning ability in 13 individuals with FRDA and 13 age- and sex-matched control participants using two experimental paradigms that examined the ability to incorporate different levels of advance information to plan sequential movements. Individuals with FRDA demonstrated a differential pattern of motor response to advance information and were significantly disadvantaged by conditions requiring initiation of movement without a direct visual cue. There was also a significant negative correlation with age of disease onset and differing levels of advance information, suggesting an impact of FRDA on the development of motor cognition, independent of the effect of disease duration. We suggest that deficits are due to cerebellar impairment disrupting cerebro-ponto-cerebello-thalamo-cerebral loops (and thus cortical function), direct primary cortical pathology or a possible combination of the two.

Cognitive domains that predict time to diagnosis in prodromal Huntington disease

BACKGROUND

Prodromal Huntington's disease (prHD) is associated with a myriad of cognitive changes but the domains that best predict time to clinical diagnosis have not been studied. This is a notable gap because some domains may be more sensitive to cognitive decline, which would inform clinical trials.

OBJECTIVES

The present study sought to characterise cognitive domains underlying a large test battery and for the first time, evaluate their ability to predict time to diagnosis.

METHODS

Participants included gene negative and gene positive prHD participants who were enrolled in the PREDICT-HD study. The CAG-age product (CAP) score was the measure of an individual's genetic signature. A factor analysis of 18 tests was performed to identify sets of measures or latent factors that elucidated core constructs of tests. Factor scores were then fit to a survival model to evaluate their ability to predict time to diagnosis.

RESULTS

Six factors were identified: (1) speed/inhibition, (2) verbal working memory, (3) motor planning/speed, (4) attention-information integration, (5) sensory-perceptual processing and (6) verbal learning/memory. Factor scores were sensitive to worsening of cognitive functioning in prHD, typically more so than performances on individual tests comprising the factors. Only the motor planning/speed and sensory-perceptual processing factors predicted time to diagnosis, after controlling for CAP scores and motor symptoms. Conclusions The results suggest that motor planning/speed and sensory-perceptual processing are important markers of disease prognosis. The findings also have implications for using composite indices of cognition in preventive Huntington's disease trials where they may be more sensitive than individual tests.

Neurocognitive signs in prodromal Huntington disease

OBJECTIVE

PREDICT-HD is a large-scale international study of people with the Huntington disease (HD) CAG-repeat expansion who are not yet diagnosed with HD. The objective of this study was to determine the stage in the HD prodrome at which cognitive differences from CAG-normal controls can be reliably detected.

METHOD

For each of 738 HD CAG-expanded participants, we computed estimated years to clinical diagnosis and probability of diagnosis in 5 years based on age and CAG-repeat expansion number (Langbehn, Brinkman, Falush, Paulsen, & Hayden, 2004). We then stratified the sample into groups: NEAR, estimated to be ≤9 years; MID, between 9 and 15 years; and FAR, ≥15 years. The control sample included 168 CAG-normal participants. Nineteen cognitive tasks were used to assess attention, working memory, psychomotor functions, episodic memory, language, recognition of facial emotion, sensory-perceptual functions, and executive functions.

RESULTS

Compared with the controls, the NEAR group showed significantly poorer performance on nearly all of the cognitive tests and the MID group on about half of the cognitive tests (p = .05, Cohen's d NEAR as large as -1.17, MID as large as -0.61). One test even revealed significantly poorer performance in the FAR group (Cohen's d = -0.26). Individual tasks accounted for 0.2% to 9.7% of the variance in estimated proximity to diagnosis. Overall, the cognitive battery accounted for 34% of the variance; in comparison, the Unified Huntington's Disease Rating Scale motor score accounted for 11.7%.

CONCLUSIONS

Neurocognitive tests are robust clinical indicators of the disease process prior to reaching criteria for motor diagnosis of HD.

Impairment in motor reprogramming in Friedreich ataxia reflecting possible cerebellar dysfunction

The cerebellar and spinocerebellar dysfunction seen in Friedreich ataxia (FRDA) has known effects on motor function. Recently, it was suggested that people with FRDA may also have impairment in motor planning, either because of cortical pathology or because of cerebello-cortical projections. Fifteen adults with FRDA and 15 matched controls completed a task requiring reciprocating movements between two buttons on a tapping board. Occasionally there was one of three "oddball" stimuli requiring reprogramming of movement. These were change in (1) direction, (2) extent or (3) direction and extent. We hypothesized that people with FRDA would have prolonged movement times due to their movement disorder, and that changes in preparation time would be affected in a way similar to controls, unless there was impairment in motor planning in FRDA. Movement execution and, to a lesser degree, movement preparation were impaired in individuals with FRDA. We argue this points to disturbed cortical function. There was a significant negative correlation between age of onset and all three reprogramming conditions, suggesting an impact of FRDA on developing motor planning. Future studies will be required to establish whether this dysfunction is due to cerebellar impairment interrupting cerebro-ponto-cerebello-thalamo-cerebral loops, primary cortical pathology or a combination of the two.

Huntington's disease affects movement termination

Huntington's disease (HD) is a neurodegenerative disease affecting the striatum and associated with deficits in voluntary movement in early stages. The final portion of aiming movements is particularly affected in HD and one hypothesis is that this deficit is linked to attention or terminal control requirements. Sixteen patients with early HD and 16 age-matched controls were examined in aiming movements. Four conditions manipulated movement termination requirements (discrete movements with a complete stop vs. cyclical back-and-forth movements) and the presence of flankers around the target. Reducing movement termination requirements significantly attenuated deficits in the final movement phase in patients. The presence of flankers around the target affected the initial portion of movements but did not affect the two groups differentially. These results indicate that terminal control requirements affect voluntary movements in HD. This suggests that frontostriatal systems are involved in movement termination.

Single unit and population responses during inhibitory gating of striatal activity in freely moving rats

The striatum is thought to be an essential region for integrating diverse information in the brain. Rapid inhibitory gating (IG) of sensory input is most likely an early factor necessary for appropriate integration to be completed. Gating is currently evaluated in clinical settings and is dramatically altered in a variety of psychiatric illnesses. Basic neuroscience research using animals has revealed specific neural sites involved in IG including the hippocampus, thalamus, brainstem, amygdala and medial prefrontal cortex. The present study investigated local IG in the basal ganglia structure of the striatum using chronic recording microwires. We obtained both single unit activations and local field potentials (LFPs) in awake behaving rats from each wire during the standard two-tone paradigm. Single units responded with different types of activations including a phasic and sustained excitation, an inhibitory response and a combination response that contained both excitatory and inhibitory components. IG was observed in all the response types; however, non-gating was observed in a large proportion of responses as well. Positive wave field potentials at 50-60 ms post-stimulus (P60) showed consistent gating across the wire arrays. No significant correlations were found between single unit and LFP measures of gating during the initial baseline session. Gating was strengthened (Tamp/Camp ratios approaching 0) following acute stress (saline injection) at both the single unit and LFP level due to the reduction in the response to the second tone. Alterations in sensory responding reflected by changes in the neural response to the initial tone were primarily observed following long-term internal state deviation (food deprivation) and during general locomotion. Overall, our results support local IG by single neurons in striatum but also suggest that rapid inhibition is not the dominant activation profile observed in other brain regions.

Proximity to clinical onset influences motor and cognitive performance in presymptomatic Huntington disease gene carriers

BACKGROUND

Neuroimaging studies of Huntington disease (HD) gene carriers have shown that characteristic striatal atrophy begins long before symptom onset, but findings regarding the presence of preclinical functional deficits are inconsistent.

OBJECTIVE

To further investigate potential motor and cognitive deficits in presymptomatic gene carriers (PSGCs), and relationships between performance and estimated proximity to HD symptom onset.

METHOD

PSGCs and age-matched controls performed motor tasks involving cued sequential button presses, and cognitive tasks involving simple and complex choice responses to visuospatial stimuli.

RESULTS

PSGCs demonstrated similar motor performance speed, and nonsignificantly slower cognitive reaction times, to controls. PSGCs made more errors than controls to stimuli requiring a spatially incongruent response, possibly suggesting some difficulty in inhibiting automatic responses. Movement times for motor conditions where little advance information was provided, and reaction times for low demand cognitive tasks, were positively correlated with PSGCs' estimated probability of symptom onset within 5 years.

CONCLUSIONS

Response speed was slower for those PSGCs estimated to have higher probabilities of close onset. These findings suggest that to provide improved knowledge of how HD begins, knowledge that may be used in clinical trials, future research should further explore relationships between function and proximity to onset.

A biomechanical study of gait initiation in Huntington's disease

BACKGROUND

Akinesia in basal ganglia disorders is essentially defined by delayed movement initiation; the reaction time increases and it becomes difficult (or even impossible) for the subject to initiate movement. A biomechanical study of gait initiation would help evaluate the role of akinesia in early stage Huntington's disease (HD) patients.

METHODS

We recorded kinematic, spatiotemporal and angular parameters (using video motion analysis, a force platform and an optoelectronic system) for the first two steps taken by 15 HD patients and 15 gender- and age-matched controls. In order to evaluate the influence of an external cue on gait initiation parameters, we studied two movement paradigms: self-triggered initiation and initiation triggered (cued) by a "beep" sound. We analyzed kinematic, spatiotemporal (the speed, length and duration of the two first steps) and angular parameters (range of joint angles) as well as kinetic data (the trajectory of the centre of pressure (COP); the speed and trajectory of the centre of mass (COM)).

RESULTS

HD patients presented akinesia in both externally triggered and self-triggered conditions. Patients had more difficulties with self-triggered gait than with triggered gait. In HD, anticipatory postural adjustments (APAs) were more impaired in self-triggered gait initiation than in cued initiation. Indeed, an alteration in the kinetic parameters revealed a reduction in first step speed in both conditions. Hypokinesia (as assessed by a reduction in the range of angle joints) played an important role in this reduction.

CONCLUSION

Akinesia is a major feature of impaired gait initiation in HD. The deficiencies in self-triggered initiation in HD seen here fit with a hypothesis whereby deficient internal cueing can be replaced by an external trigger.

Role of hypokinesia and bradykinesia in gait disturbances in Huntington's disease

OBJECTIVE

To evaluate specific patterns of locomotion in Huntington's disease (HD) and notably the respective roles of hypokinesia (i. e. a decrease in the amplitude of movement) and bradykinesia (i. e. difficulty in executing a movement, slowness) in gait disturbance.

METHODS

Kinematic, spatial (stride length, speed), temporal (cadence, speed, and stride time) and angular gait parameters (joint ankle range) were recorded in 15 early-stage HD patients by means of a video motion analysis system and then compared with 15 controls and 15 Parkinson's disease (PD) patients. Hypokinesia was studied in terms of both spatial (decrease in stride length) and angular gait parameters (decrease in joint ankle range), whereas hyperkinesia was characterized by an increase in joint ankle range. Bradykinesia (defined by a decrease in gait velocity) was also assessed in terms of temporal parameters (cadence, stride time). We studied the influence of clinical symptoms (motor dysfunction, chorea, overall disability and cognitive impairment) and the CAG repeat number on gait abnormalities.

RESULTS

we observed a clear decrease in gait speed, a decrease in cadence and an increase in stride time (i. e. bradykinesia) for HD, with significant intra-individual variability. Cadence remained normal in PD. In HD, there was no evidence for a clear decrease in stride length, although the latter is a characteristic feature of hypokinetic gait (such as that observed in PD). Angle analysis revealed the coexistence of hyperkinesia and hypokinesia in HD, which thus participate in gait abnormalities. Gait speed in HD was correlated to the motor part of the UHDRS.

CONCLUSION

Gait in HD is mainly characterized by a timing disorder: bradykinesia was present, with severe intra-individual variability in temporal gait parameters.

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.

Evidence for a disorder of locomotor timing in Huntington's disease

Disturbances of walking have been described in people with Huntington's disease (HD), although the nature of the deficits have not yet been well defined. The purpose of this investigation was to determine whether people with HD have a deficit in the regulation of footstep timing during walking. The footstep patterns of 30 people with HD and 30 matched comparisons were measured at self-selected slow, preferred, and fast speeds. Subjects were also instructed to match their footsteps to auditory metronome cues set at 80 and 120 beats per minute. Gait speed, cadence, stride length, and double limb support as a percentage of the gait cycle were measured using a computerized foot-switch system. People with HD demonstrated a disorder in their ability to regulate cadence, manifest as a reduced step frequency when walking at preferred speed and when required to increase their speed. For all walking conditions, people with HD had increased variability of footstep cadence. They also had difficulty synchronizing their footstep timing to an auditory cue. For all walking conditions, people with HD had reduced stride length. Thus, in HD, there is a disorder in the regulation of footstep timing, with increased variability, a restricted cadence range, difficulty synchronizing footsteps to an auditory cue and reduced stride length. The exact neural correlates of this timing disorder are yet to be determined.

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.

Hypometric primary saccades and increased variability in visually-guided saccades in Huntington's disease

Eye movement abnormalities can be distinctive and suggestive of a specific pathophysiology. To further investigate the deficits in the control of saccades in patients with Huntington's disease (HD), we investigated the ability of 11 HD patients and 11 matched controls to perform visually-guided saccades. We adopted reflexive saccade tasks involving predictable and unpredictable sequences, at different amplitudes of target step (10 degrees, 20 degrees, 30 degrees, 40 degrees ), as well as voluntary self-paced saccades. Prolongation of initiation was observed in the HD group as the target amplitude of predictable saccades increased. During the self-paced saccade task, the HD patients had increased intersaccadic intervals, performed fewer saccades in the allocated time and displayed an increased temporal variability in comparison to the controls. Furthermore, hypometric primary saccades, and an increased number of corrective saccades, were observed during both reflexive and voluntary saccades in the HD group. The delayed initiation of large saccades, deficits in voluntary, self-paced saccades, impaired saccadic accuracy and increased corrective saccades in HD, were interpreted in light of other ocular motor and limb studies, and appear to be due to damage to the fronto-striatal loop, including the supplementary eye fields, as well as possible brainstem and cerebellar involvement.

Quantitative assessment of daytime motor activity provides a responsive measure of functional decline in patients with Huntington's disease

Voluntary motor impairment is a functionally important aspect of Huntington's disease (HD). Therefore, quantitative assessment of disturbed voluntary movement might be important in follow-up. We investigated the relation between quantitatively assessed daytime motor activity and symptom severity in HD and evaluated whether assessment of daytime motor activity is a responsive measure in the follow-up of patients. Sixty-four consecutive HD patients and 67 age- and sex-matched healthy controls were studied. Daytime motor activity was recorded using a wrist-worn activity monitor that counts all movements during a period of five consecutive days. Patients were rated clinically for voluntary motor impairment, dyskinesias, posture & gait, depression, cognitive impairment and functional capacity. Follow-up was available from 40 patients (mean follow-up 2.0 years) and 29 controls (mean follow-up 5.9 years). Despite chorea, patients had less daytime motor activity than controls (P < 0.005). This hypokinesia correlated with impaired voluntary movements (r = 0.37; P < 0.01), disturbed posture & gait (r = 0.38; P < 0.005) and especially with reduced functional capacity (r = 0.51; P < 0.0005). During follow-up, hypokinesia remained unchanged in clinically stable patients, but became worse in those whose functional disability progressed (P < 0.005). Hypokinesia seems a core symptom of HD which is related to functional capacity. Actimetric assessment of hypokinesia is responsive to disease progression and can be used as an objective tool for follow-up.

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.

Open interconnected model of basal ganglia-thalamocortical circuitry and its relevance to the clinical syndrome of Huntington's disease

The early stages of Huntington's disease (HD) present with motor, cognitive, and emotional symptoms. Correspondingly, current models implicate dysfunction of the motor, associative, and limbic basal ganglia-thalamocortical circuits. Available data, however, indicate that in the early stages of the disease, striatal damage is mainly restricted to the associative striatum. Based on an open interconnected model of basal ganglia-thalamocortical organization, we provide a detailed account of the mechanisms by which associative striatal pathology may lead to the complex pattern of motor, cognitive, and emotional symptoms of early HD. According to this account, the degeneration of a direct and several indirect pathways arising from the associative striatum leads to impaired functioning of: (1) the motor circuit, resulting in chorea and bradykinesia, (2) the associative circuit, resulting in abnormal eye movements, "frontal-like" cognitive deficits and "cognitive disinhibition," and (3) the limbic circuit, resulting in affective and psychiatric symptoms. When relevant, this analysis is aided by comparing the symptomatology of HD patients to that of patients with mild to moderate Parkinson's disease, since in the latter there is similar dysfunction of direct pathways but opposite dysfunction of indirect pathways. Finally, we suggest a potential novel treatment of HD and provide supportive evidence from a rat model of the disease.

Movement preparation in high-functioning autism and Asperger disorder: a serial choice reaction time task involving motor reprogramming

Autism and Asperger disorder have long been associated with movement abnormalities, although the neurobehavioural details of these abnormalities remain poorly defined. Clumsiness has traditionally been associated with Asperger disorder but not autism, although this is controversial. Others have suggested that both groups demonstrate a similar global motor delay. In this study we aimed to determine whether movement preparation or movement execution was atypical in these disorders and to describe any differences between autism and Asperger disorder. A simple motor reprogramming task was employed. The results indicated that individuals with autism and Asperger disorder have atypical movement preparation with an intact ability to execute movement. An atypical deficit in motor preparation was found in Asperger disorder, whereas movement preparation was characterized by a "lack of anticipation" in autism. The differences in movement preparation profiles in these disorders were suggested to reflect differential involvement of the fronto-striatal region, in particular the supplementary motor area and anterior cingulate.

Deficits in sensorimotor control during precise hand movements in Huntington's disease

OBJECTIVES

To investigate the performance of patients with Huntington's disease (HD) while manipulating objects using a precision grip.

METHODS

The grip forces developed by the fingers were studied while subjects lifted an object of unpredictable weight in the hand. The ability to stabilize grip force after externally imposed weight change was also studied.

RESULTS

Patients used higher grip forces than the normal subjects in both the lifting and holding phases, particularly with a lighter weight. Lift timing was slowed in the patients, most markedly with a lighter weight. Increased levels of inter-trial variation were observed only with a light weight. This indicates that the slowing in HD differs from that in Parkinson's disease, which remains constant regardless of object load, and that the slowing in HD is not due to involuntary antagonist muscle activity resulting from an underlying chorea. The grip force response to sudden weight change was normal, but appeared after a delay which increased at lower rates of weight change.

CONCLUSIONS

Disturbances in precision grip timing and magnitude in HD may result from a reduced ability to process relevant tactile afferent input. The delay in the adaptive response suggests an increased threshold for detection of weight change in HD. Alternatively, this delay may arise from mediation of the response over an additional cerebellar pathway to compensate for damage to the basal ganglia.

Sub-movement cueing and motor sequence execution in patients with Huntington's disease

OBJECTIVES

We investigated whether the type of sub-movement cueing during the execution of motor sequences influences the movement time in patients with Huntington's disease.

METHODS

The kinematic variables of rapid sequential free arm movements executed with different types of sub-movement cueing - externally-triggered (ET) and self-initiated (SI) tasks - were analyzed in 7 patients and 7 healthy controls. The ET task required subjects to initiate movements in response to consecutive visual go signals; the SI task allowed them to start at will.

RESULTS

HD patients performed ET and SI tasks slower than normal subjects. Both groups executed ET sequences slower than SI, but movement times for the two tasks differed less in patients than in controls. Patients paused normally between sub-movements during the SI task, but they had slower reaction times for all the sub-movements of the ET task.

CONCLUSIONS

Slower execution of both motor tasks indicates that HD patients are bradykinetic in performing sequential free arm movements. Our finding that total movement times for SI and ET tasks differ less in patients than in controls suggests that HD impairs internal more than external cueing mechanisms.

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

The present study examined the coordination of prehensile forces during precision grip in subjects with Huntington's disease (HD). Fingertip forces were measured in 12 subjects with HD and 12 age-matched controls during the lifting of an instrumented object whose weight and surface texture were varied. The results indicate that subjects with HD have impaired initiation and delayed transitions between movement sequences and produce excessive and variable forces. However, subjects with HD demonstrated anticipatory scaling of force development based on the object's expected physical properties (planning) and adjustment of the force to the object's actual physical properties (sensorimotor integration). The observed findings generally were unrelated to the overall disease severity. However, the variability in forces was correlated with functional capacity and motor performance suggesting that variability is a key feature of the motor deficit. These results provide insights into the impaired hand function observed in individuals with HD.

Differential clinical and motor control function in a pair of monozygotic twins with Huntington's disease

We report a pair of monozygotic Huntington's disease (HD) twins who, although sharing identical CAG repeat lengths, not only present with marked differences in clinical symptoms but also behavioral abilities as measured by our experimental procedures. Both HD twins and two healthy control subjects were tested twice over 2 years. Patient A was generally more impaired at a motor level, whereas Patient B showed greater attentional impairment; Patient B, however, showed more progressive deterioration. The control subjects' performance remained consistent over the 2-year interval. Patient A clinically had the more hyperkinetic hypotonic variant of the disease, whereas Patient B, who was the more impaired, presented with a more hypokinetic hypertonic (rigid) variant. The influences of epigenetic pre- and postnatal environmental factors should not be ignored.

Analysis of gait abnormalities in Huntington disease

OBJECTIVE

To evaluate patterns of successful gait strategy in Huntington disease (HD) at various stages of illness to improve fall avoidance and maintenance of independence.

DESIGN

Repeated measurements of gait kinematic parameters and joint performance during gait cycles of six HD patients compared to 30 age-matched controls.

SETTING

A standard gait laboratory.

SUBJECTS

Six HD patients, rank-ordered for disease severity from minimal chorea to generalized dystonia, selected because they were ambulatory despite 3 to 17 years' disease duration. One patient was from a nursing home (walked with assistance) and five were living independently, either alone or with a working spouse who was the caregiver.

MAIN OUTCOME MEASURES

Standardized gait evaluations (retroreflective markers on standard bony landmarks) from five video angles, fed into digitizer to computer-generate joint angles and standard gait kinematic parameters.

RESULTS

Wide variability in gait kinematic parameters and joint interaction plots (phase plane and angle-angle plots) was observed between individuals and successive trials of the same limb, tending to increase with disease severity. Joint interaction plots show that random, highly variable distractions from planned trajectories are more apparent distally.

CONCLUSIONS

Chorea in HD does not appreciably affect the center of gravity during ambulation, and the consistency of gait profiles at heel strike shows that the ultimate target is achieved in each step despite random and frequent variability during the gait cycle.

Modeling parietal-premotor interactions in primate control of grasping

Visual information is processed in the posterior parietal cortex for the hypothesized purpose of extracting a variety of affordances for the generation of motor behavior. The term affordance is used to mean that visual cues are mapped directly to parameters that are relevant for motor interaction. In this paper, we present the FARS model of the cortical involvement in grasping, a model which focuses on the interaction between anterior intra-parietal area (AIP) and premotor area F5. The model represents the role of other intra-parietal areas, working in concert with inferotemporal cortex and F5, to provide AIP with a full range of information from which affordances may be derived. The model also suggests how task information and other constraints may resolve the action opportunities provided by multiple affordances. Our model demonstrates not only that posterior parietal cortex is a network of interacting subsystems, but also that it functions through a pattern of "cooperative computation" with a multiplicity of other brain regions. Finally, through the use of several novel tasks, the model allows us to make specific predictions regarding neural firing patterns at both the single unit and population levels, which aids in our further understanding of information encoding in these brain regions.

Performance of sequential arm movements with and without advance knowledge of motor pathways in Parkinson's disease

Patients with Parkinson's disease are slower than normal subjects in executing sequential arm movements, and their bradykinesia worsens as the execution of motor sequences progresses. In parkinsonian and normal subjects, we studied the execution of two types of fast sequential arm movements. The subjects had to perform a motor sequence following with their arm a path marked by six targets on a screen. In one experimental condition, they performed the motor sequence without advance knowledge of its path and executed each submovement in response to the consecutive appearance of the targets on the screen (unknown motor sequences). In the other condition, all the targets appeared simultaneously on the screen before the subject moved, and the subject internally determined when to execute each submovement (known motor sequences). Patients were slower than normal subjects in executing both sequences. Patients and normal subjects were faster in executing known than unknown sequences, but the patients' percentage of total movement time diminished less. During the unknown condition, both groups tended to lengthen submovement duration whereas, during the known condition, both groups tended to correct this trend. Patients performed submovements during both sequences with longer acceleration phases. The submovement symmetry ratio of the velocity profile changed according to the direction of movement (up or down). We conclude that these findings depend mainly on the model of movement execution. They also suggest that patients with Parkinson's disease have more difficulty in executing internally determined than externally triggered sequential movements.

Functional asymmetries in the movement kinematics of patients with Tourette's syndrome

OBJECTIVES

This study adopted a concurrent task design and aimed to quantify the efficiency and smoothness of voluntary movement in Tourette's syndrome via the use of a graphics tablet which permits analysis of movement profiles. In particular, the aim was to ascertain whether a concurrent task (digit span) would affect the kinematics of goal directed movements, and whether patients with Tourette's syndrome would exhibit abnormal functional asymmetries compared with their matched controls.

METHODS

Twelve patients with Tourette's syndrome and their matched controls performed 12 vertical zig zag movements, with both left and right hands (with and without the concurrent task), to large or small targets over long or short extents.

RESULTS

With short strokes, controls showed the predicted right hand superiority in movement time more strongly than patients with Tourette's syndrome, who instead showed greater hand symmetry with short strokes. The right hand of controls was less force efficient with long strokes and more force efficient with short strokes, whereas either hand of patients with Tourette's syndrome was equally force efficient, irrespective of stroke length, with an overall performance profile similar to but better than that of the controls' left hand. The concurrent task, however, increased the force efficiency of the right hand in patients with Tourette's syndrome and the left hand in controls.

CONCLUSIONS

Patients with Tourette's syndrome, compared with controls, were not impaired in the performance of fast, goal directed movements such as aiming at targets; they performed in certain respects better than controls. The findings clearly add to the growing literature on anomalous lateralisation in Tourette's syndrome, which may be explained by the recently reported loss of normal basal ganglia asymmetries in that disorder.

Effect of directed attention in Huntington's disease

This experiment sought to ascertain whether overt gaze (i.e., directed attention) would influence attentional performance in Huntington's disease (HD), via the use of a vibrotactile choice reaction time procedure involving biased probabilities of event occurrence. Subjects looked (i.e., direct gaze) either at the hand receiving the most (expected) vibrations, or the hand less often stimulated (the unexpected), for both crossed and uncrossed arm postures. Patients with HD showed performance advantages when directing attention (i.e., gaze) at the responding hand, especially for expected events. Patients with HD, however, were not sensitive to distributions of event probability in the uncrossed arm posture, nor when looking away from the responding hand. With the crossed arm posture, and when directing attention at the expected side, patients with HD became more sensitive to distributions of event probability. In HD, there may be a disruption of fronto-striatal circuitry on both cortical and subcortical levels which may account for impairments both in holding and shifting attention.

Impairments of movement kinematics in patients with Huntington's disease: a comparison with and without a concurrent task

This study aimed to quantify the efficiency and smoothness of voluntary movement in Huntington's disease (HD) by the use of a graphics tablet that permits analysis of movements profiles. In particular, we aimed to ascertain whether a concurrent task (digit span) would affect the kinematics of goal-directed movements. Twelve patients with HD and their matched controls performed 12 vertical zig-zag movements, with both left and right hands (with and without the concurrent task), to large or small circular targets over long or short extents. The concurrent task was associated with shorter movement times and reduced right-hand superiority. Patients with HD were overall slower, especially, with long strokes, and had similar peak velocities for both small and large targets, so that controls could better accommodate differences in target size. Patients with HD spent more time decelerating, especially with small targets, whereas controls allocated more nearly equal proportions of time to the acceleration and deceleration phases of movement, especially with large targets. Short strokes were generally less force inefficient than were long strokes, especially so for either hand in either group in the absence of the concurrent task, and for the right hand is its presence. With the concurrent task, however, the left hand's behavior changed differentially for the two groups; for patients with HD, it became more force efficient with short strokes and even less efficient with long strokes, whereas for controls, it became more efficient with long strokes. Controls may be able to divert attention away from the inferior left hand, increasing its automaticity, whereas patients with HD, because of disease, may be forced to engage even further online visual control under the demands of a concurrent task. Patients with HD may perhaps become increasingly reliant on terminal visual guidance, which indicates an impairment in constructing and refining an internal representation of the movement necessary for its effective execution. Basal ganglia dysfunction may impair the ability to use internally generated cues to guide movement.

Bradykinesia and movement precision in Huntington's disease

To determine whether bradykinesia in patients with Huntington's disease (HD) reflects impaired force production or an increased requirement for terminal visual guidance, 11 HD patients and matched controls performed drawing movements with varying precision requirements. Participants used an electronic pen upon a WACOM SD420 graphics tablet to join targets of either 10 or 20 mm diameter which were separated by a distance of 62.5 or 125 mm. While HD patients had slower movements, exhibiting more cycles of acceleration and deceleration, patients were not disproportionately affected by variations in target size or separation. Bradykinesia did not seem to be a product of impaired force production or increased reliance upon terminal visual guidance, since neither accelerative or decelerative phases were specifically affected by HD. However, movements of HD patients were of less consistent duration, implying variability associated with internal cues regulating movement.