Roger W. Simmons

Postural stability of diabetic patients with and without cutaneous sensory deficit in the foot

Postural stability was measured in 50 patients classified into two diabetic groups: insulin-dependent diabetes mellitus (IDDM: n = 27), and diabetic patients with bilateral cutaneous sensory deficit in the foot (CD: n = 23). All patients were matched to 50 non-diabetic controls on age, weight and gender variables. The integrity of cutaneous sensory information at the foot was assessed using a monofilament test. Static and dynamic balance was evaluated using an objective balance test involving computer-controlled dual force platforms enclosed by a visual surround. The apparatus provided six test conditions designed to systematically manipulate or eliminate visual, vestibular or somatosensory information. Scores for the six tests, and a derived composite balance score together with movement strategy scores were used for data analysis. For all six tests and composite score CD patients revealed significant postural instability compared to controls. Additionally, the CD group recorded reduced strategy scores indicating an atypical shift from ankle to hip strategy movement as postural control was stressed. IDDM patient test scores were not significantly different from control data on any pairwise comparison. Results indicated significant balance loss associated with CD putting the individual at increased risk for falling and compromising foot mechanics.

Sensory Organization Determinants of Postural Stability in Trained Ballet Dancers

Trained ballet dancers and nondancer controls completed six balance tests using computerized dynamic posturography. The tests facilitated assessment of the type of sensory organization used to maintain postural control under conditions ranging from quiet standing to a situation in which visual and/or somatosensory information was systematically removed or made unreliable. Results indicated that ballet dancers and controls have comparable balance ability during eyes open and eyes closed conditions. However, when somatosensory information alone or in combination with visual information was made unreliable, dancers were significantly less stable than controls and utilized a hip strategy to maintain postural control.

Neuromuscular responses of trained ballet dancers to postural perturbations.

The balance of trained ballet dancers and non-dancer controls was mechanically perturbed in order to evaluate the time of onset of muscle activation and the consistency of muscle activation. Results supported the prediction that ballet dancers have significantly faster long-latency (LL) neuromuscular responses than controls and are significantly more consistent in muscle activation. These findings indicate a superior postural control mechanism in trained dancers and may explain the ability of dancers to maintain static balances over a small base of support.

Motor Response Programming and Movement Time in Children with Heavy Prenatal Alcohol Exposure

The present experiment assessed motor response programming and movement time in children with histories of heavy prenatal alcohol exposure (PEA). Alcohol-exposed children between the ages of 7 and 17 years were classified into two groups: Fetal Alcohol Syndrome (FAS: n=9) and children with PEA (PEA: n=19) but who did not have the defining characteristics of FAS. The FAS and PEA children were compared with non-alcohol-exposed children (NC: n=23) when completing two tasks: a simple reaction time task (RT alone condition) and a reaction plus movement task (RT+Move condition). The movement involved responding to an imperative stimulus signal and depressing three target buttons in a set sequence. Participants completed 24 trials each for the RT alone and RT+Move response conditions. Results indicated no significant differences in performance among FAS, PEA, and NC groups during the RT alone condition. However, during the RT+Move condition, the FAS group produced significantly longer and more variable RTs than the PEA and NC groups, which produced comparable RTs. The FAS group also produced significantly slower movement times when moving to all three targets, whereas movement time variability did not significantly differ as a function of group. The observed results indicate children with FAS experience deficits in response programming and movement time production.

Coincidence Timing of Finger, Arm, and Whole Body Movements

Two experiments investigated the effects of different types of movement responses on coincidence timing skill. The view was taken that the sensory-motor integration of the movement responses would be reflected in the accuracy and consistency of anticipation timing. A Bassin anticipation timer provided a light stimulus velocity of 3 mph for both experiments and the movements studied included a simple key press using a finger, an arm movement to a key press, and whole body movements culminating with a kick or step to a target. The experiments were modelled closely on the seminal study by Grose (1967). The results of Exp. 1 supported our prediction by demonstrating superiority of the finger task over the two larger movements for all measures of coincidence timing ability. The purpose of Exp. 2 was to compare the slightly different versions of the whole body task—that used in the first experiment and that used by Grose (1967). The results confirmed the close similarity of the two movement tasks and re-affirmed the results of Exp. 1. Exp. 2 also investigated sex effects on coincidence timing ability and, in contrast to previous evidence indicating that females perform with less accuracy and consistency than do males, no significant differences were found. Analysis of practice effects showed that, although there were no significant improvements over trial blocks in Exp. 1, there were significant improvements in Exp. 2. Comparisons with other research suggests that repeated practice in solving a coincident timing problem using whole body movements can lead to improved performance. In general, the findings are consistent with the constructs of action theory and emphasize the roles perceptual and movement variables have in defining situational constraints. Also, findings indicate that proficiency in coincidence anticipation appears to be influenced by the planning and organisation required for movement execution.

Influence of stimulus symmetry and complexity upon haptic scanning strategies during detection, learning, and recognition tasks

Two experiments were conducted to investigate the perceptual processes involved in haptic exploration of randomly generated shapes. Experiment 1 required subjects to detect the symmetrical or asymmetrical characteristics of individually presented plastic shapes. The shapes also varied in complexity as measured by the number of sides. Experiment 2 involved learning a set of shapes and then attempting to recognize these “old” shapes when presented together with a series of “new” shapes. In both experiments, reaction time was investigated as a function of stimulus complexity and task requirements. Furthermore, it was observed that an initial orienting response was used to direct the subjects to adopt specific scanning strategies when examining asymmetrical or symmetrical shapes. The influences of stimulus properties and task requirements upon haptic encoding processes are discussed.

Impaired postural stability as a marker of premanifest Huntington's disease

Subtle changes in fine motor control have been observed in individuals who carry the Huntingtons disease (HD) mutation but have not yet manifested symptoms, referred to as premanifest HD (preHD). However, few studies have examined gross motor impairments in this population. This study sought to examine the role of sensory involvement in maintaining postural stability during the premanifest and manifest stages of HD using computerized dynamic posturography. Eleven HD participants, 22 preHD subdivided into “preHD Near” (<5 years from estimated clinical onset) and “preHD Far” (>5 years from estimated clinical onset), and 17 nongene carriers (NGC) completed a sensory organization test (SOT) to assess postural control when vestibular, visual, and somatosensory information was systematically degraded. The HD group demonstrated greater postural sway than the NGC and preHD Far groups on all conditions including baseline, and greater postural sway than the preHD Near group when sensory information was manipulated. The preHD Near group showed significantly greater postural sway than the preHD Far group when visual and somatosensory information was degraded and only vestibular information was available and reliable for maintaining postural stability. The results of this study highlight subtle postural deficits in the face of changing sensory conditions in preHD up to 5 years before estimated disease onset. The findings suggest that the SOT may be a highly sensitive indicator of early motor impairment and subsequent phenoconversion to manifest HD in preHD.

Peripheral regulation of stiffness during arm movements by coactivation of the antagonist muscles

Two experiments investigated whether unexpected and differential loading of a rapid, unsighted arm movement resulted in the central nervous system (CNS) regulating limb stiffness by modifying the associated neuromuscular activity. In Experiment 1, subjects completed multiple, spring-loaded training trials until a prespecified criterion of learning was attained. On selected trials, the spring load was unexpectedly replaced by an inertial load. Results indicated that to maintain positional accuracy during this inertial load trial, limb stiffness was increased by coactivating the antagonist muscles, i.e. by changing the associated neuromuscular activity from a predominantly triphasic pattern to one of coactivation. In Experiment 2, the sequence of loading was reversed producing a change in the required limb stiffness from a relatively high to low level. This change was observed as a pattern of coactivation being replaced by a triphasic activity pattern. These results support the notion that limb stiffness is regulated primarily through modification of the neuromuscular activity pattern prior to movement termination. It was also demonstrated that the size of the unexpected load did not affect the basic activation pattern selected by the CNS. It is proposed that the signal which triggers the CNS to regulate limb stiffness is based on peripheral information generated as a result of agonist activity occurring during the first part of the movement.

Children with Heavy Prenatal Alcohol Exposure Exhibit Deficits when Regulating Isometric Force

BACKGROUND Production of isometric (i.e., constant) force is an essential component of performing everyday functional tasks, yet no studies have investigated how this type of force is regulated in children with confirmed histories of heavy prenatal alcohol exposure. METHODS Children 7 to 17 years old with heavy prenatal alcohol exposure (n = 25) and without exposure (n = 18) applied force to a load cell to generate an isometric force that matched a criterion target force displayed on a computer monitor. Two levels of target force were investigated in combination with 3 levels of visual feedback frequency that appeared on the computer monitor as a series of yellow dots. Force was maintained for 20 seconds and participants completed 6 trials per test condition. RESULTS Root-mean-square error, signal-to-noise ratio, and sample entropy indexed response accuracy, response variability, and signal complexity, respectively. The analyses revealed that in comparison with controls, children with gestational ethanol exposure were significantly less accurate and more variable in regulating their force output and generated a response signal with greater regularity and less complexity in the time domain. CONCLUSIONS Children with prenatal alcohol exposure experience significant deficits in isometric force production that may impede their ability to perform basic motor skills and activities in everyday tasks.

The effects of muscle activation on postural stability in diabetes mellitus patients with cutaneous sensory deficit in the foot

Activity of the lower leg muscles in response to an unexpected disturbance to upright standing was studied in diabetic patients and non-diabetic matched controls. The diabetic individuals were classified into two groups: diabetic patients with normal cutaneous sensitivity in the foot (n=27) and patients with cutaneous sensory deficit (n=23). All participants completed twenty trials standing on a force platform that rotated upward 8 deg at 50 deg/s. This movement produced short-latency and medium-latency responses in the gastrocnemius muscle and a single long-latency response in the anterior tibialis. All muscle activity was assessed using electromyography techniques. Results indicated that the average delay of the short-, medium- and long-latency responses produced by the diabetic groups was comparable to control group values. However, the within subject variability associated with activating the anterior tibialis was found to be statistically greater for the cutaneous deficit diabetic group. Additionally, fifty percent of the CD group failed to produce an observable stretch reflex response. The results suggest that the inability to generate a neuromuscular response with consistent temporal patterning is a contributing factor to greater postural sway observed in diabetic patients with cutaneous sensory deficit in the foot.