Lisa M. Muratori

Spectrum of gait impairments in presymptomatic and symptomatic Huntington's disease.

The purpose of this study was to quantify gait impairments in presymptomatic and symptomatic Huntingtons disease (HD) subjects, and examine sensitivity of gait measures. Our sample (n = 65) included presymptomatic mutation carriers (PMC) (n = 15), symptomatic HD subjects (SHD) (n = 30) and healthy controls (n = 20). Participants were requested to walk at their preferred speed on a computerized walkway that recorded spatiotemporal variables. We administered the Unified HD Rating Scale (UHDRS) for PMC and SHD. PMC demonstrated decreased gait velocity (P < 0.01), stride length (P < 0.008), and increased time in double support (P < 0.001); and demonstrated higher variability in stride length (P < 0.01) and step time (P < 0.004) compared with controls. These impairments worsened with increasing disease severity for SHD. Gait impairments were correlated with predicted years to onset in PMC (velocity = −0.65; cadence = −0.70, step time = 0.71) and demonstrated high sensitivity and specificity in distinguishing between controls and mutation carriers. In contrast, UHDRS scores did not reveal impairments in gait and balance. Gait bradykinesia and dynamic balance impairments begin in the presymptomatic stage of HD and continue to worsen in the symptomatic stages. Gait measures are sensitive in differentiating between mutation positive and negative individuals even when impairments were not detected by clinical neurological examination.

Cell phones change the way we walk

Cell phone use among pedestrians leads to increased cognitive distraction, reduced situation awareness and increases in unsafe behavior. Performing a dual-task, such as talking or texting with a cell phone while walking, may interfere with working memory and result in walking errors. At baseline, thirty-three participants visually located a target 8m ahead; then vision was occluded and they were instructed to walk to the remembered target. One week later participants were assigned to either walk, walk while talking on a cell phone, or walk while texting on a cell phone toward the target with vision occluded. Duration and final location of the heel were noted. Linear distance traveled, lateral angular deviation from the start line, and gait velocity were derived. Changes from baseline to testing were analyzed with paired t-tests. Participants engaged in cell phone use presented with significant reductions in gait velocity (texting: 33% reduction, p=0.01; talking: 16% reduction, p=0.02). Moreover, participants who were texting while walking demonstrated a 61% increase in lateral deviation (p=0.04) and 13% increase in linear distance traveled (p=0.03). These results suggest that the dual-task of walking while using a cell phone impacts executive function and working memory and influences gait to such a degree that it may compromise safety. Importantly, comparison of the two cell phone conditions demonstrates texting creates a significantly greater interference effect on walking than talking on a cell phone.

Applying principles of motor learning and control to upper extremity rehabilitation

The purpose of this article is to provide a brief review of the principles of motor control and learning. Different models of motor control from historical to contemporary are presented with emphasis on the Systems model. Concepts of motor learning including skill acquisition, measurement of learning, and methods to promote skill acquisition by examining the many facets of practice scheduling and use of feedback are provided. A fictional client case is introduced and threaded throughout the article to facilitate understanding of these concepts and how they can be applied to clinical practice.

Clinical measurement of mobility and balance impairments in Huntington's disease: validity and responsiveness.

BACKGROUND Mobility and balance in Huntingtons disease (HD) are currently assessed in the clinic with three items from the unified Huntingtons disease rating scale (UHDRS): walk, tandem and pull tests. These tests may not be optimal because they are scored on an ordinal scale and do not test anticipatory balance. We tested the validity and responsiveness of three clinical tests of mobility and balance. METHODS Three clinical tests (FRT, timed up and go (TUG), Berg balance scale (BBS)) were validated with seven quantitative gait measures and two indicators of functional limitation (HD-ADL and total functional capacity) in 30 subjects with HD. These tests were also assessed for responsiveness to disease severity. RESULTS FRT and BBS were correlated with five quantitative gait measures, and TUG with eight (all p<0.05). All tests were correlated with indicators of functional limitation (p<0.05) and were responsive to disease severity. CONCLUSIONS FRT, TUG and BBS are valid, responsive and easy to administer clinical tests that should be routinely included with the UHDRS in therapeutic trials for subjects with HD.

Impaired anticipatory control of force sharing patterns during whole-hand grasping in Parkinson’s disease

We examined the coordination of multi-digit grasping forces as they developed during object grasping and lifting. Ten subjects with Parkinson’s disease (PD; OFF and ON medication) and ten healthy age-matched control subjects lifted a manipulandum that measured normal forces at each digit and the manipulandum’s position. The center of mass (CM) was changed from trial to trial in either a predictable (blocked) or unpredictable (random) order. All subjects modulated individual fingertip forces to counterbalance forces exerted by the thumb and minimize object tilt after lift-off. However, subjects with PD OFF exhibited an impaired ability to use anticipatory mechanisms resulting in less differentiated scaling of individual finger forces to the object CM location. Remarkably, these between-group differences in force modulation dissipated as subjects reached peak grip forces during object lift, although these occurred significantly later in subjects with PD OFF than controls and PD ON. Analysis of the tilt of the object during lift revealed all subjects had similar deviations of the object from the vertical, the direction of which depended on CM location. Thus these findings in subjects with PD indicate that: (a) PD-induced impairments in anticipatory force mechanisms appear to be greatly increased in multi-digit grasping as opposed to previous reports from two-digit grasping; (b) inaccurate scaling of fingertip force amplitude and sharing patterns before object lift is recovered during object lift; (c) the implementation of appropriate force amplitude and sharing among the digits during the lift occurs significantly later than for controls; (d) medication improves the temporal recovery of multi-digit force coordination. These results are discussed within the framework of PD-related deficits in sensorimotor integration and control of multi-degrees of freedom movement.

Haptic feedback from manual contact improves balance control in people with Parkinson's disease

Parkinsons disease (PD) degrades balance control. Haptic (touch and proprioception) feedback from light contact with a stationary surface inadequate to mechanically stabilize balance improves balance control in healthy people. In this study we tested whether PD impairs use of haptic cues independent of mechanical support to control balance. We measured postural sway in thirteen individuals with PD (H&Y 1-3, median=2, Q1=2, Q3=2) and thirteen age-matched controls balancing in a widened, sharpened Romberg stance in four conditions: eyes-closed, no manual contact; eyes-closed light-touch contact (<1N), eyes-closed, unrestricted contact; and eyes-open, no contact. To determine whether PD-severity affects any of these balance strategies, PD participants were tested on- and off-medication, and using the more- and less-affected body side in the stance and manual contact. Individuals with PD simultaneously maintained non-supportive fingertip contact and balance in this task without practice. PD participants swayed more than control participants (ML CP p=0.010; shoulder p<0.001), but manual contact reduced sway. Non-supportive manual contact stabilized balance more than vision (p<0.05). PD-severity factors had no significant effect (p>0.05). We conclude the effect of PD on balance is not specific to vision or haptic feedback. Nevertheless, haptic cues from manual contact, independent of mechanical support, improve balance control in individuals with PD. We discuss the implication that PD or associated dopaminergic pathways do not directly affect haptic feedback balance control mechanisms, including arm/posture coordination and proprioceptive integration.

Control of multidigit grasping in Parkinson's disease: effect of object property predictability

We examined the extent to which subjects with Parkinsons disease (PD) modulate normal fingertip forces during five-digit grasping based on the objects center of mass (CM). We also tested the effect of trial-to-trial predictability of CM location on the distribution of all fingertip forces relative to thumb force. Ten right-handed subjects with PD (OFF and ON medication) and 10 healthy age-matched control subjects participated. Subjects lifted a manipulandum that measured normal forces exerted by each digit. The CM location was changed from trial-to-trial either in an unpredictable (random) or predictable (blocked) order. Discriminant analysis and information theory were used to quantify the extent to which force-sharing patterns could be discriminated as a function of CM location. All subjects modulated fingertip normal forces as a function of CM location regardless of its predictability, although larger forces were employed when its location was unpredictable. However, in controls, normal force modulation of individual fingers to the objects CM location occurred over a greater range of forces when the CM location was predictable than when it was unpredictable. In contrast, subjects with PD exhibited a similar force modulation to CM location regardless of its predictability. There was a clearer discrimination of force-sharing patterns when the CM location was predictable for controls but not for subjects with PD OFF medication. Medication improved the time course of normal force modulation to CM location. These results indicate that subjects with PD maintained the ability to modulate individual fingertip forces to the objects physical properties. Nevertheless, subjects with PD did not benefit from the a priori knowledge of object CM location to the same extent as controls. These findings support the notion that PD affects the ability to use anticipatory control mechanisms.

Building a framework for a dual task taxonomy.

The study of dual task interference has gained increasing attention in the literature for the past 35 years, with six MEDLINE citations in 1979 growing to 351 citations indexed in 2014 and a peak of 454 cited papers in 2013. Increasingly, researchers are examining dual task cost in individuals with pathology, including those with neurodegenerative diseases. While the influence of these papers has extended from the laboratory to the clinic, the field has evolved without clear definitions of commonly used terms and with extreme variations in experimental procedures. As a result, it is difficult to examine the interference literature as a single body of work. In this paper we present a new taxonomy for classifying cognitive-motor and motor-motor interference within the study of dual task behaviors that connects traditional concepts of learning and principles of motor control with current issues of multitasking analysis. As a first step in the process we provide an operational definition of dual task, distinguishing it from a complex single task. We present this new taxonomy, inclusive of both cognitive and motor modalities, as a working model; one that we hope will generate discussion and create a framework from which one can view previous studies and develop questions of interest.

Tactile/proprioceptive integration during arm localization is intact in individuals with Parkinson's disease.

It has been theorized that sensorimotor processing deficits underlie Parkinsons disease (PD) motor impairments including movement under proprioceptive control. However, it is possible that these sensorimotor processing deficits exclude tactile/proprioception sensorimotor integration: prior studies show improved movement accuracy in PD with endpoint tactile feedback, and good control in tactile-driven precision-grip tasks. To determine whether tactile/proprioceptive integration in particular is affected by PD, nine subjects with PD (off-medication, UPDRS motor=19-42) performed an arm-matching task without visual feedback. In some trials one arm touched a static tactile cue that conflicted with dynamic proprioceptive feedback from biceps brachii muscle vibration. This sensory conflict paradigm has characterized tactile/proprioceptive integration in healthy subjects as specific to the context of tactile cue mobility assumptions and the intention to move the arm. We found that the individuals with PD had poorer arm-matching accuracy than age-matched control subjects. However, PD-group accuracy improved with tactile feedback. Furthermore, sensory conflict conditions were resolved in the same context-dependent fashion by both subject groups. We conclude that the somatosensory integration mechanism for prioritizing tactile and proprioception feedback in this task are not disrupted by PD, and are not related to the observed proprioceptive deficits.

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.