Postural Motor Control Research Articles

What If Low Back Pain Is the Most Prevalent Parkinsonism in the World?

Low back pain (LBP) has a point prevalence of nearly 10% and ranks highest in global disease burden for years lived with disability; Parkinson’s disease (PD) ranks in the top 100 most disabling health conditions for years lost and years lived with disability (1). Recent evidence suggests that people with chronic, recurrent LBP exhibit many postural impairments reminiscent of a neurological postural disorder such as PD. We compare and contrast postural impairments associated with LBP and PD in order to inform treatment strategies for both conditions. The literature suggests that both LBP and PD associate with impaired proprioceptive function, sensory orientation during standing balance, anticipatory postural adjustments, automatic postural responses, and striatal-cortical function. Although postural impairments are similar in nature for LBP and PD, the postural impairments with LBP appear more specific to the trunk than for PD. Likewise, although both health conditions associate with altered striatal-cortical function, the nature of the altered neural structure or function differ for PD and LBP. Due to the high prevalence of LBP associated with PD, focused treatment of LBP in people with PD may render benefit to their postural impairments and disabilities. In addition, LBP would likely benefit from being considered more than just a musculoskeletal injury; as such, clinicians should consider including approaches that address impairments of postural motor control.

POSTURAL-MOTOR CONTROL CHARACTERISTICS IN OLDER FEMALE FALLERS

The paper presents data on the characteristics of a postural-motor control (PMC) in female fallers 65-74 years old (twice or more fallers during a year). Evaluation of PMC parameters was carried out using computer posturographic (stabilometric) complex «Balance Master». «Sit to stand» test analysis showed a rate decrease in the average rise index (p = 0,009) and a rate increase in the average speed of the gravity center (GC) oscillation (p = 0,003) in older women with F. Comparative evaluation of the test «Walk Across» found a decline in the average step length (p = 0,042) and the average speed of walking (p = 0,029) in the surveyed female fallers. Characteristics of the test «Tandem Walk» showed a rate decrease in the average final GC oscillation (p

Elderly Use Proprioception Rather than Visual and Vestibular Cues for Postural Motor Control.

Multiple factors have been proposed to contribute to the deficits of postural control in the elderly. They were summarized as sensory, motor, and higher-level adaptation deficits. Using a model-based approach, we aimed to identify which of these deficits mainly determine age-related changes in postural control. We analyzed postural control of 20 healthy elderly people with a mean age of 74 years. The findings were compared to data from 19 healthy young volunteers (mean age 28 years) and 16 healthy middle-aged volunteers (mean age 48 years). Postural control was characterized by spontaneous sway measures and measures of perturbed stance. Perturbations were induced by pseudorandom anterior–posterior tilts of the body support surface. We found that spontaneous sway amplitude and velocity were significantly larger, and sway frequencies were higher in elderly compared to young people. Body excursions as a function of tilt stimuli were clearly different in elderly compared to young people. Based on simple feedback model simulations, we found that elderly favor proprioceptive over visual and vestibular cues, other than younger subjects do. Moreover, we identified an increase in overall time delay challenging the feedback systems stability, and a decline in the amplitude of the motor feedback, probably representing weakness of the motor system. In general, these parameter differences between young and old may result from both deficits and compensation strategies in the elderly. Our model-based findings correlate well with deficits measured with clinical balance scores, which are widely used in clinical practice.

Functional connectivity underlying postural motor adaptation in people with multiple sclerosis.

A well-characterized neural network is associated with motor learning, involving several brain regions known to have functional and structural deficits in persons with multiple sclerosis (PwMS). However, it is not known how MS affects postural motor learning or the neural networks involved. The aim of this study was to gain a better understanding of the neural networks underlying adaptation of postural responses within PwMS. Participants stood on a hydraulically driven, servo-controlled platform that translated horizontally forward and backward in a continuous sinusoidal pattern across multiple trials over two consecutive days. Our results show similar postural adaptation between PwMS and age-matched control participants despite overall deficits in postural motor control in PwMS. Moreover, PwMS demonstrated better retention the following day. PwMS had significantly reduced functional connectivity within both the cortico-cerebellar and cortico-striatal motor loops; neural networks that subserve implicit motor learning. In PwMS, greater connectivity strength within the cortico-cerebellar circuit was strongly related to better baseline postural control, but not to postural adaptation as it was in control participants. Further, anti-correlated cortico-striatal connectivity within the right hemisphere was related to improved postural adaptation in both groups. Taken together with previous studies showing a reduced reliance on cerebellar- and proprioceptive-related feedback control in PwMS, we suggest that PwMS may rely on cortico-striatal circuitry to a greater extent than cortico-cerebellar circuitry for the acquisition and retention of motor skills.

Are articulatory settings mechanically advantageous for speech motor control?

We address the hypothesis that postures adopted during grammatical pauses in speech production are more “mechanically advantageous” than absolute rest positions for facilitating efficient postural motor control of vocal tract articulators. We quantify vocal tract posture corresponding to inter-speech pauses, absolute rest intervals as well as vowel and consonant intervals using automated analysis of video captured with real-time magnetic resonance imaging during production of read and spontaneous speech by 5 healthy speakers of American English. We then use locally-weighted linear regression to estimate the articulatory forward map from low-level articulator variables to high-level task/goal variables for these postures. We quantify the overall magnitude of the first derivative of the forward map as a measure of mechanical advantage. We find that postures assumed during grammatical pauses in speech as well as speech-ready postures are significantly more mechanically advantageous than postures assumed during absolute rest. Further, these postures represent empirical extremes of mechanical advantage, between which lie the postures assumed during various vowels and consonants. Relative mechanical advantage of different postures might be an important physical constraint influencing planning and control of speech production.

Statistical analysis of constriction task and articulatory posture variables during speech and pausing intervals using real-time magnetic resonance imaging

We have shown previously using real-time magnetic resonance imaging data (Ramanarayanan etal., 2011, ISSP Montreal) that it is more likely that articulatory posture variables (such as jaw angle) are controlled to achieve articulatory settings during pausing intervals in read speech than constriction task variables (such as lip aperture, tongue tip constriction degree, etc.). In this study, we extend this work to examine correlations between constriction task variables and articulatory posture variables during both speech and pause intervals. This work serves to deepen our understanding of the differences in postural motor control of the vocal tract observed during speaking and pausing. [Work supported by NIH.]

Reviewer’s comments concerning “Altered breathing patterns during lumbopelvic motor control tests in chronic low back pain: a case–control study” (J. Nijs et al., ESJO-D-08-00264 R2)

Reviewer’s comments concerning “Altered breathing patterns during lumbopelvic motor control tests in chronic low back pain: a case–control study” (J. Nijs et al., ESJO-D-08-00264 R2)

Interactions of breathing with the postural regulation of the fingers

Objectives: The present study was performed to detect the interactions between breathing and the postural motor control of the fingers. A previous study revealed a scattering in the intraindividual motor responses which resembled a grouping. It is hypothesized to result from the influence of breathing. Methods: Torque impulses and torque steps at two intensities were applied to 17 healthy volunteers, to the II–IV fingers of their right hand. The subjects had to compensate for these additional torque loads that were triggered by a breathing-related signal and elicited at 4 different moments within a breath. Results: We demonstrated mutual influences between breathing and the regulation of finger posture. The reaction to a torque load was faster at the beginning of inspiration but more precise when the torque load was applied in mid-expiration. The motor response to torque loads was accompanied by changes in the breathing time course, particularly when the torque load was elicited during inspiration. The effects were most pronounced when torque steps were applied. The intensity of torque loads had no significant influence. Additionally, we observed that the respiratory phase-transitions often coincided with the end of the applied torque steps. Conclusions: The results correspond well with the interactions existing between breathing and single or rhythmical movements. Further investigations of motor functions should consider this interdependence with breathing.

The timing of primary orthostatic tremor bursts has a task-specific plasticity.

Primary orthostatic tremor is characterized by unsteadiness and shakiness of the legs while standing. It is due to a remarkably strong and regular EMG modulation at approximately 16 Hz that is thought to be of CNS origin. Previous studies have shown that the tremor frequency is the same in all involved muscles and that the time relation between bursts of activity in different muscles may be fixed (e.g. always co-contracting or always contracting in an alternating pattern). Here we have used frequency domain analysis of postural muscle EMG signals in five primary orthostatic tremor patients and in two normal controls to explore the nature of such fixed timing patterns. The timing is found not to relate simply to the relative conduction times for passage of rhythmic bursts from a central oscillation to different muscles. Indeed, although the timing pattern (expressed as phase) of the 16-Hz EMG bursts in different postural muscles remains constant while the subject adopts a certain steady posture, it is different for different subjects and also changes when the same subject adopts a different posture. It seems unlikely that such complex task-dependent timing relations of rhythmic postural muscle activity are due to the primary pathology of primary orthostatic tremor. Instead, we suggest that the abnormally strong peripheral manifestation of a 16-Hz CNS oscillation merely unmasks normal central processes so that the timing patterns may provide a clue to the nature of postural motor control.

Sensory and motor interdependence in postural adjustments

The sensory reafference from a movement depends upon the movement, and the movement chosen depends upon the available senses, as demonstrated by vestibular patients who abandon certain movements. Often, one variable is assumed to be dependent whereas the other is independent; however, sensory and motor dynamics in posture are interdependent as conditions upon each other. This paper applies conditional dynamics to characterize the global structure of interdependence between sensory states and motor strategies in fast postural adjustments. The mathematical formalism incorporates rich but disparate experimental, clinical, and theoretical results about sensory and motor control of posture. The control structures presented include relatively stable anatomical, physiological, and functional structures, both continuous and discrete, leading to a composite functional logic for the coordination of these structures in sensorimotor control. Results include sensorimotor control structures for postural adjustments for healthy subjects and certain types of vestibular patients. The sensorimotor control structures for patients with absent vestibular function suggest implications for management of the deficit.

Influence of artificial saddle riding on postural stability in children with cerebral palsy.

Stability of quiet upright stance was investigated in 25 children with cerebral palsy at the beginning and the end of a 3-month period of therapy involving 20 min microprocessor-controlled saddle riding, performed twice a week. The traditional parameters of postural sway based on the centre-of-pressure analysis (range, standard deviation, mean speed and mean radius) dropped significantly over time confirming advantageous influence of this treatment. As a complementary tool, an autoregressive modelling technique was used allowing us to establish after each single ride considerable decreases in the frequency of the feet adjustments, which represent the control variable of the postural system in sagittal plane. These changes reflect diminished ankle joints stiffness resulting from a single session, and are supposedly a basic reason for substantial progress of the patients. The autoregressive approach proved to be a powerful method, which corroborates and reinforces stabilographic investigations. The findings confirm that the therapy led to a noteworthy improvement in the postural performance of the CP children in sagittal as well in frontal planes. Moreover, they let us to infer about biomechanical properties of joints involved in maintaining posture, thus giving more insight into the operation of the neuro-muscular system and allowing us to better understand the reason of progress in motor control of posture.

Force regulation is deficient in patients with parietal lesions: a system-analytic approach

By means of a quantitative system-analytic investigation strategy, the postural motor control of the fingers was evaluated, to characterise the possible deficit of force regulation in patients with parietal lesions. In spite of a normal response to short torque pulses, the parietal-lesion patients had difficulties in returning to the preload level after the application of an additional step torque load to fingers II–IV of their left or right hands. The control offset (measured 500 ms after step torque application) was significantly larger in the patient group. This deficit in the investigated patients with parietal lesions to compensate for step torque loads was not due to a paresis, but rather resulted from a disturbance in the generation of a sufficient counterforce against the applied step torque within an adequate time window and motor pattern. This distinct force-regulation deficit was found in patients with left- and right-sided parietal lesions.

Chapter 23 Abnormal postural control associated with peripheral vestibular disorders

The development of a systematic approach to the diagnosis and management of ataxias of vestibular origin depends critically on the elucidation of the complex sensory and motor interactions involved in human postural control. In this paper, the results of studies of both sensory and motor control of posture in adults and children with peripheral vestibular deficits are summarized and reviewed. In studies of the sensory organization of postural control, normal subjects and patients with peripheral vestibular deficits were exposed to unreliable information from their support surface and/or visual surround during quiet stance. While normal adults and children were able to maintain balance under these conditions, the majority of children and adults with peripheral vestibular deficits showed one or both of the following abnormalities: (1)Vestibular loss patients were unable to maintain equilibrium when forced to rely on vestibular information for postural control. (2)Vestibular distortion patients were unable to select an accurate source of sensory information when exposed to sensory conflicts during quiet stance. Preliminary results of studies of motor coordination in these patients also suggest that vestibular loss patients rely almost exclusively on ankle sway to control posture, even during balance tasks which require hip movements to maintain equilibrium. In contrast, some vestibular distortion patients appear to rely on hip motions, even when not required to do so to maintain balance. The results of these studies are discussed in terms of the implications for both sensory and motor aspects of postural control in patients with ataxias of vestibular origin.

Locomotor hypokinesia in the reserpine-treated rat: Drug effects from the corpus striatum and nucleus accumbens

A mechanographic method was used to assess the locomotor performance induced by apomorphine or other dopaminergic drugs inreserpine-treated rats. Reserpine was found to induce locomotor hypokinesia. The hypokinesia was dose-dependently reversed by apomorphine (APO), bromocriptine and pergolide. Locomotion was induced by microinjection of APO into the nucleus accumbens. No locomotor effect was found after injection into corpus striatum. Injection into both nuclei was not superior to accumbens only. Intra-striatal or intraaccumbens injections of trifluoperazine blocked the effect on locomotion by systematic apomorphine. The results confirmed that reserpine-induced locomotor hypokinesia is reversed by dopaminergic stimulation in the nucleus accumbens. There were indications that blockade of striatal or accumbens' dopamine receptors counteracts apomorphine-induced l locomotion presumably by interaction with postural motor control. Evidence was found for separate dopaminergic control of locomotion and muscletone. This may be of importance for the development of new antiparkinson drugs.

Computer applications in human neurophysiological research

The interaction between the voluntary direct motor control system and the follow-up postural motor control system is examined in normal human subjects. The state of the alpha motoneuron pool is measured by eliciting a Hoffmann reflex while a subject is making a voluntary movement. A digital process computer is used on-line for the control of the experiment and for data recording and analysis. It is proposed that the control signals for the voluntary movements studied appear directly at the alpha motoneuron where they exert an influence over the muscle activity which is independent of the Ia feedback. Simultaneously, some descending control signals exert a presynaptic influence on the Ia terminals, which permit regulation of the excitability of the monosynaptic pathway independently of the alpha motoneuron activity.