Neuroscience

Decoding kinetic parameters of grasping movements from single unit activity in monkey motor cortex

Development of neuronal prosthetics, where neuronal activity is used to control artificial limbs, has so far relied on decoding kinematic parameters of movements, such as movement position or velocity. In addition to kinematic control, proper control of forces exerted by the prosthetic device is necessary for successful interaction with the environment. In our study, we analysed the possibility of classifying and decoding different grasp related forces during active grasping. Two macaque monkeys were trained to reach, grasp and pull an object in response to visual cues. Cues instructed the monkeys to grasp the object with one out of two grip types (precision or side grip) and pull the object with one of two different forces (0.5N or 2N). Monkeys obtained a food reward after successfully performing the instructed grip and pull. During the task execution, we recorded electrophysiological signals from the multielectrode arrays implanted intracortically in the hand and arm area of the monkey’s motor cortex. Six different parameters of the grip: four pressure forces on each side of the object, pull force on the object and the object displacement, were recorded simultaneously with the neuronal activity. Recorded neuronal activity was used to classify different grip types or loading forces, and to decode the continuous traces of different forces during the grip. Our results show that kinetic grip parameters can be decoded with high accuracy, thereby improving the feasibility of constructing fully functional anthropomorphic neuronal prosthesis that relies on kinetic (force) control.


Listed In: Biomechanical Engineering, Neuroscience


Metrics of multi-muscle synergies in Parkinson’s disease: Analysis of variance and motor equivalence

Over the past years, we have developed a test for postural stability based on the theory of synergies stabilizing salient performance variables. In this study, effects of Parkinson's disease (PD) and dopamine-replacement therapy on multi-muscle synergies stabilizing the center of pressure (COP) coordinate were explored between: (1) a cohort of 11 patients without clinically identifiable postural problems (Hoehn-Yahr stage II) and 11 age-matched controls, and (2) a cohort of 10 patients tested off- and on-medication, with and without postural problems (stage II and III, n = 5 per stage). Participants stood on a force platform and performed cyclical body sway at 0.5 Hz along the anterior-posterior direction. Electromyographic signals from 13 leg and trunk muscles were used to compute: (1) the amount of inter-cycle variance that did not affect (VUCM) and affected (VORT) COP coordinate, and (2) the magnitude of the cycle-to-cycle motion that did not change (motor equivalent: ME) and changed (non-motor equivalent: nME) the COP coordinate. We hypothesized that both methods would produce indices sensitive to PD and dopaminergic medications. Compared to controls, patients showed significantly smaller inter-cycle VUCM and ME components suggesting a less flexible, and hence less stable, behavior. Moreover, inter-cycle variance within/orthogonal to the UCM correlated with ME/nME displacements. Results suggest clinical utility of variance and motor equivalence analyses of postural instability in early stages of PD and quantifying the effects of dopamine-replacement drugs. The analysis of motor equivalence is particularly attractive because it requires only a handful of trials (observations).
Listed In: Neuroscience


Characterising gait over different walking speeds in patients with bilateral vestibular loss: preliminary results

Bilateral vestibular hypofunction (BVH) is a bilateral reduction or loss of vestibular function resulting in balance deficits and an increased falls risk. As part of a larger study, this experiment aimed to assess how spatiotemporal gait characteristics and their variability change across different walking speeds in patients with BVH. Nine patients (55±15y) with BVH have participated thus far. Experiments were conducted on the CAREN Extended system (Motekforce Link, Amsterdam, The Netherlands). Following multiple familiarisation trials, the participants completed five recorded two minute walking bouts at different speeds (0.6m/s, 0.8m/s, 1.0m/s, 1.2m/s and 1.4m/s). 60 strides per speed were analysed and the means, standard deviations and coefficients of variation (CV) of stride length and time, step length and width, double support time and swing phase toe clearance were calculated. Stride length, step length and toe clearance all increased with increases in walking speed (P<0.001). Stride and double support time decreased with increased walking speed (P<0.0001). No walking speed effect was found for step width (P=0.25). Significant reductions in variability with increases in walking speed were found for stride length, stride time, step length, toe clearance (P<0.01) and double support time (P<0.05). A significant increase in step width variability was observed with increases in walking speed (P=0.0033). These preliminary data suggest that while anteroposterior gait characteristics may improve in terms or variability with increases in walking speed in these patients, mediolateral motions may become more variable, which may have implications for mediolateral stability and falls risk in patients with BVH.
Listed In: Biomechanics, Gait, Neuroscience


MUSCULAR FATIGUE INFLUENCES MOTOR SYNERGIES DURING PUSH-UPS

Objectives: The conventional push-up is a popular exercise used by the American College of Sports Medicine to test participant muscular endurance. Push-ups require changes in the ground reaction forces generated at each point of contact with the ground (all four extremities) which are achieved through muscular contractions. Although this exercise is common, the motor control mechanisms used in this motion are relatively unknown. We investigated whether humans adjust individual limb forces (push-up synergies) as they reached volitional fatigue and evaluated the hypothesis that muscular fatigue influences synergistic actions between the forces produced at the hand contact points. Approach: Twenty-one volunteers participated in a single motion capture trial where they performed as many push-ups as possible, stopping at self-determined failure. Push-ups were completed to a controlled three-beat rhythm (down, up, hold plank) at a rate of 24 repetitions per minute. Participants were instructed to arrange themselves in a plank position with each extremity within the bounds of an embedded force platform and analog data was collected at a frequency of 1000Hz. An index of synergy, defined as correlations between vertical forces, was calculated for every downward and upward motion within the push-up trial. Findings: Between-arm vertical forces were positively correlated during upward and downward motion. Positive correlation indicates that limbs worked together to produce increases or decreases needed for center of mass movement. Upward limb synergy significantly (p ≤ 0.00) decreased as participants neared volitional fatigue while downward limb synergy did not significantly change (p = 0.77). Conclusions: We found that muscular fatigue affected the synergistic actions between limbs in upward motion but not in downward motion. After muscular fatigue, between arm synergy was reduced only during concentric muscle contractions. Public Health Significance: Better understanding the synergistic changes produced by fatigue could be used to evaluate or better understand control changes behind pathologic gait or movement adaptations.
Listed In: Biomechanical Engineering, Biomechanics, Neuroscience


Balancing sensory inputs: Sensory reweighting of vision and ankle proprioception during a bipedal posture task

Multisensory integration is driven by a process of sensory reweighting during which each input is assigned a weight depending on the current functional state of a particular sensory system, the task itself and the context in which it is being performed. The primary aim of this study was to determine which of the two inputs between ankle proprioception and vision is upweighed during a postural control task when the two inputs provide conflicting information pertaining to direction of body sway. Achilles tendon vibration and visual flow were used to create sensory conflict, which produced center of pressure (COP) sway in opposite directions when applied independently. The baseline conditions (1) consisted of eyes open quiet stance condition, eyes closed with vibration applied on the Achilles tendons (2) and eyes open with visual flow (3). The experimental condition simultaneously combined vibration and visual flow. COP excursions were recorded in 10 healthy young adults to evaluate the magnitude and direction of sway produced by vibration and/or visual flow. Additionally, lower body joint kinematics were evaluated to understand the multi-segmental strategies and their adaptation to the various sensory manipulations. The results showed that visual flow moderated the extent of backward COP and ankle angular displacement produced when vibration was applied independently. Additionally, visual flow was also found to reduce the extent of predominant hip strategy generated by ankle vibration. The findings show that visual input plays a significant role in maintaining stability and that ankle proprioception is downweighed during conflicts between vision and proprioception. This has important implication for balance training using controlled visual flow in patients with balance disorders and elderly.
Listed In: Biomechanics, Neuroscience, Posturography


ESTIMATION OF OPTIMAL STIMULUS AMPLITUDE FOR BALANCE TRAINING USING ELECTRICAL STIMULATION OF THE VESTIBULAR SYSTEM

Sensorimotor changes such as postural and gait instabilities can affect the functional performance of astronauts after gravitational transitions. When astronauts are trained before flight with supra-threshold noisy, stochastic vestibular stimulation (SVS), the central nervous system can be trained to reweight sensory information by using veridical information from other sensory inputs (such as vision and proprioception) for postural and gait control. This reweighting, in turn, can enhance functional performance in novel gravitational environments. However, the optimal maximum amplitude of stimulation has not yet been identified that can simulate the effect of deterioration in vestibular inputs for preflight training or for evaluating vestibular contribution in functional tests in general. Most studies have used arbitrary but fixed maximum current amplitudes from 3 to 5 mA in the mediolateral (ML) direction to disrupt balance function in both ML and anterior-posterior directions in healthy adults. The goal of this study was to determine the minimum SVS level that yields an equivalently degraded balance performance. Fourteen subjects stood on a compliant surface with their eyes closed and were instructed to maintain a stable upright stance. Measures of stability of the head, trunk, and whole body were quantified in the ML direction. Objective perceptual motion thresholds were estimated ahead of time by having subjects sit on a chair with their eyes closed and giving 1-Hz bipolar binaural sinusoidal electrical stimulation at various current amplitudes. Results from the balance task suggest that using stimulation amplitudes of 280% of motion-perceptual threshold (~2.2 mA on average) significantly degraded balance performance.


Listed In: Biomechanics, Neuroscience, Posturography


Dance May Improve Quality of Life But Not Gait in Individuals with Parkinson’s Disease

Purpose: Research supports the use of ballroom dance to improve balance in individuals with Parkinson’s disease (PD). This study used the Mark Morris Dance for PD program as a template for dance classes to examine the effects of dance on gait, balance, and quality of life in individuals with PD. Subjects : Eleven individuals with mild to moderate PD participated in the study. Methods : A trained instructor led dance classes for subjects once a week for 12 weeks. Participants were encouraged to use the Mark Morris Dance for PD At Home DVD twice a week for 45 minutes. Classes included a 20 min. seated warm up; a 20 min. supported standing portion focused on balance and strength; and 30 min. partnered movements for swing, shag, or tango. Data collected before and after the intervention included gait parameters (Protokinetics Zeno walkway), sway area (AMTI force platform) during mCTSIB, Mini-BESTest, Falls Efficacy Scale, Apathy Scale and PDQ-39. A paired-samples t-test was performed. Results : Participants had significant decrease in apathy following the intervention (P = 0.018). A significant decrease in the percentage of the double support phase of gait indicated individuals spent less time with both feet in contact with the ground (P = 0.019). Conclusions : An instructor-led dance class based on the Dance for PD program once per week for 12 weeks improved certain aspects of quality of life, but not necessarily gait and balance. Further research with increased frequency of supervised dance classes is indicated.
Listed In: Gait, Neuroscience, Physical Therapy


&#039;Moving Forward&#039;: Gait, Cognition and Associated Risk Factors: Insights from SHARE and TILDA

The established pathway of cognitive decline identifies Mild Cognitive Impairment (MCI) as a common pre-dementia syndrome. As MCI can represent the endpoint of cognitive decline or a transient state, more predictive diagnostic tools are required. A new pre-dementia syndrome, Motoric Cognitive Risk (MCR) syndrome, has been proposed. It is defined by slow gait and cognitive complaints but absence of dementia and mobility disability. MCR aims to improve on the predictive power of MCI, this study aims to explore it’s claim. Associations have been uncovered between differing cognitive domains and specific characteristics of gait. Leveraging the gait-cognitive function relationship is a novel approach to potentially highlighting those experiencing cognitive decline. However, the diagnostic tool of MCR is a new construct and currently imperfect, its efficacy not fully validated and sensitivity for dementia prediction relatively unknown. Reliable data on prevalence and risk factors help contribute to this validation process. In this presentation prevalence data for a multi-country aging study and a nationally representative community dwelling aging study will be presented. The variables available in both datasets which will be of interest in this study include; Gait Speed, Global Cognition (Mini-Mental State Exam (MMSE) score), Presence of Cognitive Complaints, Age, Body Mass Index (BMI), Dementia diagnosis (reported or imputed) and Waist Circumference. This study will inform the following research project, which will aim to assess whether specific gait components or combinations alone are better than the MCR construct in their association to cognitive decline.
Listed In: Gait, Neuroscience


Sensory contributions to standing balance in unilateral vestibulopathy

Patients with unilateral peripheral vestibular disorder (UPVD) have diminished postural stability and therefore the aim of this study was to examine the contribution of multiple sensory systems to postural control in UPVD. Seventeen adults with UPVD and 17 healthy controls participated in this study. Centre of pressure (COP) trajectories were assessed using a force plate during six standing tasks: Forwards and backwards leaning, and standing with and without Achilles tendon vibration, each with eyes open and eyes closed. Postural stability was evaluated over 30s by means of: total COP excursion distance (COPPath) and the distances between the most anterior and posterior points of the COPPath and the anterior and posterior anatomical boundaries of the base of support (COPAmin and COPPmin). In addition, the corrected COPAmin and COPPmin was assessed by taking the corrected base of support boundaries into account using the anterior and posterior COP data from the leaning tasks. UPVD patients showed a tendency for smaller limits of stability during the leaning tasks in both directions. Subject group and task condition effects were found (P<0.05) for COPPath, (i.e. higher values for patients compared to controls). UPVD patients showed lower (P<0.05) COPPmin values compared to the control group for all conditions (more pronounced with the corrected COPPmin). Disturbance of the visual system alone lead to a distinct postural backward sway in both subject groups which became significantly more pronounced in combination with Achilles tendon vibration. The individual limits of stability should be considered in future research when conducting posturographic measurements.
Listed In: Biomechanics, Neuroscience, Physical Therapy, Posturography


Static postural control does not strongly predict dynamic gait stability recovery following a trip in adults with and without vestibular dysfunction

Unilateral peripheral vestibular disorder (UPVD) negatively affects upper and lower body motor performance, but postural control during quiet stance in UPVD patients has not been directly compared with dynamic stability control after an unexpected perturbation during locomotion. We analysed centre of pressure (COP) characteristics during static posturography in UPVD patients and healthy controls and compared this with performance of a trip recovery task. 17 UPVD patients and 17 healthy controls were unexpectedly tripped while walking on a treadmill. The margin of stability (MoS) was calculated at touchdown (TD) of the perturbed step and the first six recovery steps. Posturography was used to assess postural stability during 30 seconds of standing with eyes open and closed using a force plate. The trip reduced the MoS of the perturbed leg (p<0.05) with no significant differences in MoS between the groups. Controls returned to MoS baseline level in five steps and patients did not return within the six steps. UPVD patients showed a greater total COP sway path excursion (closed eyes only), anterior-posterior range of COP distance and a more posterior COP position in relation to the posterior boundary of the base of support. There were no significant correlations between COP sway path excursion and MoS values. We concluded that UPVD patients have a diminished ability to control and recover dynamic gait stability after an unexpected trip and lower static postural stability control compared to healthy matched controls, but that trip recovery and static postural control rely on different control mechanisms.
Listed In: Biomechanics, Gait, Neuroscience, Physical Therapy, Posturography