Sensory reweighting of postural control requires distinct rambling and trembling sway adaptations.

Background: Implementation of the Sensory Organization Test (SOT) under the rambling-trembling (RM-TR) framework allows for an examination of both individual sensory contributions and compensatory mechanisms, a valuable insight in research and clinical settings. Such investigation could substantially improve our ability to assess and treat fall risk in older adults and people living with neurological disorders.

Research Question: How are RM and TR components of sway influenced by SOT-induced challenges in healthy adults?

Methods: Twenty-three healthy adults (27.

Subthreshold white noise vibration alters trembling sway in older adults.

Background: Somatosensory deficit is a significant contributor to falls in older adults. Stochastic resonance has shown promise in recent studies of somatosensation-based balance disorders, improving many measures of stability both inside and outside of the clinic. However, our understanding of this effect from a physiological perspective is poorly understood.

Rambling-trembling center-of-pressure decomposition reveals distinct sway responses to simulated somatosensory deficit.

Background: Falls in older adults are often multifactorial, but can be linked to diminished sensation capabilities from age-related neural degeneration. Rambling-trembling (RM-TR) decomposition may provide insight into the relation between sensorineural function and postural sway, with both research and clinical applications.

Research Question: What are the effects of perturbed somatosensation on RM-TR-derived measures of center of pressure (COP) during quiet standing?

Methods: Fifty-two healthy young adults (22.

Muscle Synergies Obtained from Comprehensive Mapping of the Cortical Forelimb Representation Using Stimulus Triggered Averaging of EMG Activity.

Neuromuscular control of voluntary movement may be simplified using muscle synergies similar to those found using non-negative matrix factorization. We recently identified synergies in electromyography (EMG) recordings associated with both voluntary movement and movement evoked by high-frequency long-duration intracortical microstimulation applied to the forelimb representation of the primary motor cortex (M1). The goal of this study was to use stimulus-triggered averaging (StTA) of EMG activity to investigate the synergy profiles and weighting coefficients associated with poststimulus facilitation, as synergies may be hard-wired into elemental cortical output modules and revealed by StTA.

Muscle synergies obtained from comprehensive mapping of the primary motor cortex forelimb representation using high-frequency, long-duration ICMS.

Simplifying neuromuscular control for movement has previously been explored by extracting muscle synergies from voluntary movement electromyography (EMG) patterns. The purpose of this study was to investigate muscle synergies represented in EMG recordings associated with direct electrical stimulation of single sites in primary motor cortex (M1). We applied single-electrode high-frequency, long-duration intracortical microstimulation (HFLD-ICMS) to the forelimb region of M1 in two rhesus macaques using parameters previously found to produce forelimb movements to stable spatial end points (90-150 Hz, 90-150 μA, 1,000-ms stimulus train lengths).

The characterization of a base-width neutral step as the first step for balance recovery in moderate Parkinson's disease.

Purpose: The purpose of this study is to characterize the base-width neutral step (BNS) as the first step in a compensatory step response in persons with moderate Parkinson's disease (PD), and its effect on balance recovery.

Materials And Methods: Ten PD and 10 healthy controls (HCs) responded to a posterior waist pull. A BNS was defined if the first step was less than 50 mm.

Timing of Cortico-Muscle Transmission During Active Movement.

Numerous studies have reported large disparities between short cortico-muscle conduction latencies and long recorded delays between cortical firing and evoked muscle activity. Using methods such as spike- and stimulus-triggered averaging of electromyographic (EMG) activity, previous studies have shown that the time delay between corticomotoneuronal (CM) cell firing and onset of facilitation of forelimb muscle activity ranges from 6.7 to 9.

Equilibrium-based movement endpoints elicited from primary motor cortex using repetitive microstimulation.

High-frequency, long-duration intracortical microstimulation (HFLD-ICMS) is increasingly being used to deduce how the brain encodes coordinated muscle activity and movement. However, the full movement repertoire that can be elicited from the forelimb representation of primary motor cortex (M1) using this method has not been systematically determined. Our goal was to acquire a comprehensive M1 forelimb representational map of movement endpoints elicited with HFLD-ICMS, using stimulus parameters optimal for evoking stable forelimb spatial endpoints.

Effective intracortical microstimulation parameters applied to primary motor cortex for evoking forelimb movements to stable spatial end points.

High-frequency, long-duration intracortical microstimulation (HFLD-ICMS) applied to motor cortex is recognized as a useful and informative method for corticomotor mapping by evoking natural-appearing movements of the limb to consistent stable end-point positions. An important feature of these movements is that stimulation of a specific site in motor cortex evokes movement to the same spatial end point regardless of the starting position of the limb. The goal of this study was to delineate effective stimulus parameters for evoking forelimb movements to stable spatial end points from HFLD-ICMS applied to primary motor cortex (M1) in awake monkeys.

The effect of moderate Parkinson's disease on compensatory backwards stepping.

Postural instability is a major unmet need in the treatment of Parkinson's disease (PD) and its progression is not well understood. This study examined compensatory stepping taken in response to a backwards waist pull in participants with moderate PD (H&Y III) compared to age-range matched healthy controls (HC). The first step in the response was quantified in terms of strategy, temporal, kinematic, and center of pressure (COP) parameters previously observed to be significantly different in mild PD (H&Y II) compared to HC.

Effects of age and localized muscle fatigue on ankle plantar flexor torque development.

Background And Purpose: Older adults often experience age-related declines in strength, which contribute to fall risk. Such age-related levels of fall risk may be compounded by further declines in strength caused by acute muscle fatigue. Both age- and fatigue-related strength reductions likely impact the ability to quickly develop joint torques needed to arrest falls.

Age-related differences in kinetic measures of landing phase lateral stability during a balance-restoring forward step.

Lateral stability during stepping is critical to successful balance recovery, and has been previously studied from a kinematics perspective. However, relatively little is known about the kinetic aspects of lateral stability. The purpose of this paper is to investigate age-related changes in laterally directed landing phase ground and joint reactions during a balance-restoring step response.

Postural sway in patients with mild to moderate Parkinson's disease.

Clinical assessment of postural instability in persons with Parkinson's disease (PD) is done with the retropulsive pull test, but since this test does not assess the underlying causes of postural instability, there is a need for additional assessment tools. The aim of this study was to identify postural sway parameters for use in a multifactorial approach to quantify postural instability. Nineteen adults diagnosed with idiopathic PD, 14 healthy age-matched controls (EH), and 10 healthy young adults (YH) completed the study.

Early biomechanical markers of postural instability in Parkinson's disease.

Current clinical assessments do not adequately detect the onset of postural instability in the early stages of Parkinson's disease (PD). The aim of this study was to identify biomechanical variables that are sensitive to the effects of early Parkinson's disease on the ability to recovery from a balance disturbance. Ten adults diagnosed with idiopathic PD and no clinically detectable postural instability, and ten healthy age-range matched controls (HC) completed the study.

A novel device to measure power grip forces in squirrel monkeys.

Understanding the neural bases for grip force behaviors in both normal and neurologically impaired animals is imperative prior to improving treatments and therapeutic approaches. The present paper describes a novel device for the assessment of power grip forces in squirrel monkeys. The control of grasping and object manipulation represents a vital aspect of daily living by allowing the performance of a wide variety of complex hand movements.

Discrete bandwidth visual feedback increases structure of output as compared to continuous visual feedback in isometric force control tasks.

Background: Performance variability measures provide a partial picture of force control ability. Nonlinear analyses can reveal important information related to the randomness and complexity of the data, providing a more complete picture of the physiological process.

Methods: We investigated the effects of visual feedback on the structure and performance of the force output from isometric force control tasks.

Impaired grip force modulation in the ipsilesional hand after unilateral middle cerebral artery stroke.

Understanding grasping control after stroke is important for relearning motor skills. The authors examined 10 individuals (5 males; 5 females; ages 32-86) with chronic unilateral middle cerebral artery (MCA) stroke (4 right lesions; 6 left lesions) when lifting a novel test object using skilled precision grip with their ipsilesional ("unaffected") hand compared to healthy controls (n = 14; 6 males; 8 females; ages 19-86). All subjects possessed normal range of motion, cutaneous sensation, and proprioception in the hand tested and had no apraxia or cognitive deficits.

Effects of step length on stepping responses used to arrest a forward fall.

This study investigated effects of step length on the stepping response used to arrest an impending forward fall. Twelve healthy young (mean age 22, S.D.

The use of correlation integrals in the study of localized muscle fatigue of elbow flexors during maximal efforts.

Innovative applications of non-linear time series analysis have recently been used to investigate physiological phenomena. In this study, we investigated the feasibility of using the correlation integral to monitor the localized muscle fatigue process in the biceps brachii during sustained maximal efforts. The subjects performed isometric maximum contractions until failure in elbow flexion (90 degrees from neutral).

Ipsilateral deficits of targeted movements after stroke.

Objective: To test the hypotheses that targeted movements of both the ipsilateral and the contralateral extremities of stroke survivors would be prolonged compared with those from a control group without stroke, and that the ipsilateral deficit would occur in movements toward small, but not large, targets.

Design: Descriptive study.

Setting: Motor performance laboratory.

The effects of age and feedback on isometric knee extensor force control abilities.

Objective: To investigate the effects of age and feedback on submaximal isometric force control abilities in the knee extensors.

Design: Analysis of a force control task in a quasi-experimental design.

Background: The ability to control submaximal strength is important to accomplish activities of daily living.

Effects of age, step direction, and reaction condition on the ability to step quickly.

Background: The ability to take a step quickly is important for balance maintenance during activities of daily living. The purpose of this study was to investigate the effects of age, reaction condition, and step direction on the ability to take a volitional step as fast as possible.

Methods: The performance of a voluntary step task was measured in young adult (mean age 20, SD 0.