Andrea Cristina de Lima-Pardini

Aging increases flexibility of postural reactive responses based on constraints imposed by a manual task

This study compared the effect of stability constraints imposed by a manual task on the adaptation of postural responses between 16 healthy elderly (mean age = 71.56 years, SD = 7.38) and 16 healthy young (mean age = 22.94 years, SD = 4.82) individuals. Postural stability was perturbed through unexpected release of a load attached to the participant’s trunk while performing two versions of a voluntary task: holding a tray with a cylinder placed with its flat side down (low constraint) or with its rolling round side down (high constraint). Low and high constraint tasks were performed in alternate blocks of trials. Results showed that young participants adapted muscular activation and kinematics of postural responses in association with previous experience with the first block of manual task constraint, whereas the elderly modulated postural responses based on the current manual constraint. This study provides evidence for flexibility of postural strategies in the elderly to deal with constraints imposed by a manual task.

Precueing time but not direction of postural perturbation induces early muscular activation: comparison between young and elderly individuals.

In this study, we evaluated the effect of precueing characteristics of an impending perturbation to upright stance on reactive responses of distal leg muscles. Young and older individuals were compared in a task of recovering stable upright stance following rotation of the supporting platform to induce anterior or posterior body sway. Directions of the supporting platform rotation were randomized across trials. Immediately before postural perturbation participants were cued about direction and/or time of platform rotation, or performed the task under directional and temporal uncertainty of the impending perturbation. Results showed that precueing time of perturbation led to earlier muscular activation onset, while precueing perturbation direction did not modulate either latency or magnitude of muscular activation. Those effects were similar between age groups. Our findings suggest that awareness of the perturbation time favored shorter response latencies in both the young and older individuals.

Keeping your balance while balancing a cylinder: interaction between postural and voluntary goals

The present study investigated whether postural responses are influenced by the stability constraint of a voluntary, manual task. We also examined how task constraint and first experience (the condition with which the participants started the experiment) influence the kinematic strategies used to simultaneously accomplish a postural response and a voluntary task. Twelve healthy, older adults were perturbed during standing, while holding a tray with a cylinder placed with the flat side down (low constraint, LC) or with the rolling, round side down (high constraint, HC). Central set changed according to the task constraint, as shown by a higher magnitude of both the gastrocnemius and tibialis anterior muscle activation bursts in the HC than in the LC condition. This increase in muscle activation was not reflected, however, in changes in the center of pressure or center of mass displacement. Task constraint influenced the peak shoulder flexion for the voluntary tray task but not the peak hip flexion for the postural task. In contrast, first experience influenced the peak hip flexion but not the peak shoulder flexion. These results suggest an interaction between two separate control mechanisms for automatic postural responses and voluntary stabilization tasks.

An fMRI-compatible force measurement system for the evaluation of the neural correlates of step initiation

Knowledge of brain correlates of postural control is limited by the technical difficulties in performing controlled experiments with currently available neuroimaging methods. Here we present a system that allows the measurement of anticipatory postural adjustment of human legs to be synchronized with the acquisition of functional magnetic resonance imaging data. The device is composed of Magnetic Resonance Imaging (MRI) compatible force sensors able to measure the level of force applied by both feet. We tested the device in a group of healthy young subjects and a group of elderly subjects with Parkinson’s disease using an event-related functional MRI (fMRI) experiment design. In both groups the postural behavior inside the magnetic resonance was correlated to the behavior during gait initiation outside the scanner. The system did not produce noticeable imaging artifacts in the data. Healthy young people showed brain activation patterns coherent with movement planning. Parkinson’s disease patients demonstrated an altered pattern of activation within the motor circuitry. We concluded that this force measurement system is able to index both normal and abnormal preparation for gait initiation within an fMRI experiment.

Balance and fear of falling in subjects with Parkinson's disease is improved after exercises with motor complexity

Resistance training with instability (RTI) uses exercises with high motor complexity that impose high postural control and cognitive demands that may be important for improving postural instability and fear of falling in subjects with Parkinsons disease (PD). Here, we hypothesized that: 1) RTI will be more effective than resistance training (RT) in improving balance (Balance Evaluation Systems Test [BESTest] and overall stability index [Biodex Balance System®]) and fear of falling (Falls Efficacy Scale-International [FES-I] score) of subjects with Parkinsons disease (PD); and 2) changes in BESTest and FES-I after RTI will be associated with changes in cognitive function (Montreal Cognitive Assessment [MoCA] score - previously published) induced by RTI. Thirty-nine subjects with moderate PD were randomly assigned to a nonexercising control, RT, and RTI groups. While RT and RTI groups performed progressive RT twice a week for 12 weeks, the RTI group added progressive unstable devices to increase motor complexity of the resistance exercises. There were significant group × time interactions for BESTest, overall stability index, and FES-I scores (P < 0.05). Only RTI improved BESTest, overall stability index and FES-I scores, and RTI was more effective than RT in improving biomechanical constraints and stability in gait (BESTest sections) at post-training (P < 0.05). There were strong correlations between relative changes in BESTest and MoCA (r = 0.72, P = 0.005), and FES-I and MoCA (r = -0.75, P = 0.003) after RTI. Due to the increased motor complexity in RTI, RTI is recommended for improving balance and fear of falling, which are associated with improvement in cognitive function of PD.

Measuring cortical motor hemodynamics during assisted stepping – An fNIRS feasibility study of using a walker

Walkers are commonly prescribed worldwide to individuals unable to walk independently. Walker usage leads to improved postural control and voluntary movement during step. In the present study, we aimed to provide a concept-proof on the feasibility of an event-related protocol integrating the analyses of biomechanical variables of step initiation and functional near-infrared spectroscopy (fNIRS) to measure activation of the supplementary motor area (SMA) while using a walker. Healthy young participants were tested while stepping with versus without the use of the walker. Behavioral analysis showed that anticipatory postural adjustments (APA) decreased when supporting the body weight on the walker. Delta (without-with) of activation magnitude of the muscle tibialis anterior was positively correlated to the delta of deoxyhemoglobin concentration changes in the SMA. The novelty of this study is the development of a protocol to assess brain function together with biomechanical analysis during the use of a walker. The method sheds light to the potential utility of combining fNIRS and biomechanical assessment during assistive step initiation, which can represent a new opportunity to study populations with mobility deficits.

Effects of spinal cord stimulation on postural control in Parkinson's disease patients with freezing of gait

Freezing of gait (FoG) in Parkinson’s disease (PD) is an incapacitating transient phenomenon, followed by continuous postural disorders. Spinal cord stimulation (SCS) is a promising intervention for FoG in patients with PD, however, its effects on distinct domains of postural control is not well known. The aim of this study is to assess the effects of SCS on FoG and distinct domains of postural control. Four patients with FoG were implanted with SCS systems in the upper thoracic spine. Anticipatory postural adjustment (APA), reactive postural responses, gait and FoG were biomechanically assessed. In general, the results showed that SCS improved FoG and APA. However, SCS failed to improve reactive postural responses. SCS seems to influence cortical motor circuits, involving the supplementary motor area. On the other hand, reactive posture control to external perturbation that mainly relies on neuronal circuitries involving the brainstem and spinal cord, is less influenced by SCS.

Young and older adults adapt automatic postural responses equivalently to repetitive perturbations but are unable to use predictive cueing to optimize recovery of balance stability

Processing of contextual cues has been proposed to modulate the generation of automatic postural responses to unanticipated balance perturbations. In this investigation, we compared young and older individuals in responses to sudden rotations of the support base inducing either planti- or dorsiflexion of the ankles. Assessment was made in conditions resulting from the combination of visual directional cueing of the forthcoming platform rotation, and block versus random sequences of platform rotation directions. Results showed that, for both rotation directions, the block sequence led to reduced magnitude of activation of distal agonist muscles and direction-specific modulation of ground reaction forces to recover body balance. Visual directional cueing, conversely, failed to modulate either muscular responses or forces applied to the support base through the feet for balance recovery. Effects were similar between ages, suggesting that aging does not increase the influence of cognition on the generation of automatic postural responses, and that adaptation to repeated postural perturbations over trials is preserved in healthy older individuals.

Dramatic improvement of tardive dyskinesia movements by inline skating

A 25-year-old woman with severe tardive dyskinesia (TD) due to neuroleptics had substantial improvement of movements while inline skating (video at Neurology.org). She received pallidal deep brain stimulation (DBS), and gait and inline skating were assessed before and after DBS; her twin sister served as a control (figures 1 and 2). Possible explanations for her improvement include (1) balance stability required by inline skating provides external cues that are less prominent during gait1; and (2) dystonia consistently responds to geste antagoniste.2 Since TD has variable response to treatments, we propose research into alleviating factors in TD that may advance treatment and rehabilitation in this incapacitating disorder.