Effect of sit-stand workstation position and computer task on head and trunk postural sway and discomfort.

Adjustable-height desks may provide musculoskeletal health benefits to offset the effects of prolonged sitting. One mechanism may be increased postural variability, here characterized by head and trunk postural sway. Linear acceleration of the head and trunk were measured while participants used computer workstations in seated and standing positions during keyboard and mouse tasks; secondary measures were discomfort and proprioception (head and neck repositioning error). Median accelerations of the head and trunk were 20-26% lower in mouse tasks compared to keyboard tasks (p < 0.01). There were no significant differences in sway parameters between seated and standing positions. Discomfort and proprioception were correlated; subjects who experienced increased neck discomfort after 1.5 h of computer work had almost twice the head and neck repositioning error. The results suggest that postural sway is more affected by different tasks (keyboard vs. mouse) than by different workstation configurations and that low proprioception acuity may relate to the development of discomfort.

Altered coordination strategies during upright stance and gait in teachers of the Alexander Technique.

Deterioration in movement and posture often occurs with aging. Yet there may be approaches to movement training that can maintain posture and movement coordination patterns as we age. The Alexander Technique is a non-exercise-based approach that aims to improve everyday movement and posture by increasing awareness and modulating whole-body postural muscle activity. This study assessed whether nineteen 55-72-year-old Alexander Technique teachers showed different posture and movement coordination patterns than twenty age-matched controls during a standing and walking protocol using 3D inertial sensors. During upright stance, Alexander Technique teachers showed lower centroidal sway frequency at the ankle (p = .04) and lower normalized jerk at the sternum (p = .05) than controls. During gait, Alexander Technique teachers had more symmetrical gait cycles (p = .04), more symmetrical arm swing velocity (p = .01), greater arm swing velocity (p < .01), greater arm swing range of motion (p = .02), and lower range of acceleration of the torso in the frontal plane (p = .03) than controls. Smoother control of upright posture, more stable torso motion, and less restrained arm mobility suggest that Alexander Technique training may counter movement degradation that is found with aging. Results highlight the important balance between mobility and stability within the torso and limbs.

Postural instructions affect postural sway in young adults.

BACKGROUND: Instructions to exert effort to correct one's posture are ubiquitous, but previous work indicates that effort-based postural instructions can impair balance control in older adults with and without neurodegenerative disease. Although less-studied, young adults are at high risk of injurious falls. RESEARCH QUESTION: How do different postural instructions influence static balance in young adults? METHODS: Single-session, counterbalanced, within-subjects design. Twenty young adults briefly practiced three different ways of thinking about their posture, then attempted to employ each way of thinking while standing on springy foam for 30 s with eyes open. Relax instructions were used as a baseline between experimental conditions. Effort-based instructions emulated popular concepts of posture correction using muscular exertion. Light instructions aimed at encouraging length and width while reducing excess tension. Postural sway was assessed with an inertial sensor at the low back. RESULTS: Effort-based postural instructions increased path length and jerk of postural sway during quiet stance, relative to Light and Relaxed instructions. SIGNIFICANCE: These results are consistent with previous work in older adults indicating that thinking of upright posture as inherently effortful impairs balance. Therefore, the common practice of instructing young adults to use effortful posture may impair their balance performance.

Posture biofeedback increases cognitive load.

Attention may be important for actively maintaining posture during computer tasks, resulting in a dual-task tradeoff, where maintaining posture through extrinsic feedback imposes cognitive load. Mindfulness may make intrinsic postural feedback (which imposes less cognitive load) more available. Therefore, we hypothesized that the use of biofeedback would improve posture and negatively impact game performance; additionally, higher levels of mindfulness would be associated with lower game performance costs in the biofeedback condition. Healthy young adult participants played a challenging computer game for 10 min with and without neck length biofeedback, in a counterbalanced repeated-measures design. For each condition, we assessed posture using neck shrinkage (percentage of best), and task performance (computer game score). Neck length was better retained and game performance was worse with biofeedback than without, consistent with the hypothesis that posture biofeedback imposed a cognitive load. In addition, participants with the most neck shrinkage suffered the greatest performance decrements from using biofeedback, and neck length retention during the task without biofeedback was associated with lower self-reported daily neck pain and higher self-reported mindfulness. Thus, those with the greatest need for postural feedback suffer the greatest performance decrements from extrinsic feedback. The results are consistent with the idea that mindfulness enables people to use intrinsic feedback to maintain posture without imposing a dual-task cost.

Lighten Up! Postural Instructions Affect Static and Dynamic Balance in Healthy Older Adults.

BACKGROUND AND OBJECTIVES: Increased fall risk in older adults is associated with declining balance. Previous work showed that brief postural instructions can affect balance control in older adults with Parkinson's disease. Here, we assessed the effects of brief instructions on static and dynamic balance in healthy older adults. RESEARCH DESIGN AND METHODS: Nineteen participants practiced three sets of instructions, then attempted to implement each instructional set during: (1) quiet standing on foam for 30 s with eyes open; (2) a 3-s foot lift. "Light" instructions relied on principles of reducing excess tension while encouraging length. "Effortful" instructions relied on popular concepts of effortful posture correction. "Relax" instructions encouraged minimization of effort. We measured kinematics and muscle activity. RESULTS: During quiet stance, Effortful instructions increased mediolateral jerk and path length. In the foot lift task, Light instructions led to the longest foot-in-air duration and the smallest anteroposterior variability of the center of mass, Relax instructions led to the farthest forward head position, and Effortful instructions led to the highest activity in torso muscles. DISCUSSION AND IMPLICATIONS: Thinking of upright posture as effortless may reduce excessive co-contractions and improve static and dynamic balance, while thinking of upright posture as inherently effortful may make balance worse. This may partly account for the benefits of embodied mindfulness practices such as tai chi and Alexander technique for balance in older adults. Pending larger-scale replication, this discovery may enable physiotherapists and teachers of dance, exercise, and martial arts to improve balance and reduce fall risk in their older students and clients simply by modifying how they talk about posture.

Brain networks associated with anticipatory postural adjustments in Parkinson's disease patients with freezing of gait.

Specific impairments of anticipatory postural adjustment (APA) during step initiation have been reported in patients with Parkinson's disease (PD) and freezing of gait (FoG). Although APA disruption has been associated with FoG, there is scarce knowledge about its neural correlates. We sought to better understand the neural networks involved with APA in patients with FoG by assessing the level of hemodynamic response of specific brain regions and the functional connectivity during the leg lifting task. In the current investigation, APAs of patients with PD, with and without (nFoG) freezing were assessed during a leg lifting task in an event-related, functional magnetic resonance imaging (er-fMRI) protocol. Results identified a high hemodynamic response in the right anterior insula (AI) and supplementary motor area (SMA) in the FoG group when an APA was required. The nFoG had stronger connectivity between the right and left insulae than the FoG group. The strength of this connectivity was negatively correlated with the severity of FoG. Both groups showed different brain network organizations comprising the SMA and the bilateral AI. The SMA was found to be a hub in patients with FoG when an APA was required for the task. Our findings suggest that both groups used compensatory mechanism comprising the insulae during APA. Neither group used the entire network comprised of the insulae and SMA to accomplish the task. The FoG group relied more on SMA as a hub than as part of a broader network to exchange information during the APA.

Neck posture is influenced by anticipation of stepping.

BACKGROUND: Postural deviations such as forward head posture (FHP) are associated with adverse health effects. The causes of these deviations are poorly understood. We hypothesized that anticipating target-directed movement could cause the head to get "ahead of" the body, interfering with optimal head/neck posture, and that the effect may be exacerbated by task difficulty and/or poor inhibitory control. METHOD: We assessed posture in 45 healthy young adults standing quietly and when they anticipated walking to place a tray: in a simple condition and in conditions requiring that they bend low or balance an object on the tray. We defined FHP as neck angle relative to torso; we also measured head angle relative to neck and total neck length. We assessed inhibitory control using a Go/No-Go task, Stroop task, and Mindful Attention Awareness Scale (MAAS). RESULTS: FHP increased when participants anticipated movement, particularly for more difficult movements. Worse Stroop performance and lower MAAS scores correlated with higher FHP. False alarms on the Go/No-Go task correlated with a more extended head relative to the neck and with shortening of the neck when anticipating movement. CONCLUSIONS: Maintaining neutral posture may require inhibition of an impulse to put the head forward of the body when anticipating target-directed movement.

Preliminary evidence for feasibility, efficacy, and mechanisms of Alexander technique group classes for chronic neck pain.

OBJECTIVES: To determine feasibility and potential of Alexander technique (AT) group classes for chronic neck pain and to assess changes in self-efficacy, posture, and neck muscle activity as potential mechanisms for pain reduction. DESIGN: A single-group, multiple-baseline design, with two pre-tests to control for regression toward the mean, a post-test immediately after the intervention, and another post-test five weeks later to examine retention of benefits. Participants were predominately middle-aged; all had experienced neck pain for at least six months. INTERVENTION: Participants attended ten one-hour group classes in AT, an embodied mindful approach that may reduce habitual overactivation of muscles, including superficial neck muscles, over five weeks. OUTCOME MEASURES: (1) self-reports: Northwick Park Questionnaire (to assess neck pain and associated disability) and Pain Self-Efficacy Questionnaire; (2) superficial neck flexor activation and fatigue (assessed by electromyography and power spectral analysis) during the cranio-cervical flexion test; (3) posture during a video game task. RESULTS: There were no significant changes in outcomes between pre-tests. All participants completed the intervention. After the intervention: (1) participants reported significantly reduced neck pain; (2) fatigue of the superficial neck flexors during the cranio-cervical flexion test was substantially lower; (3) posture was marginally more upright, as compared to the second pre-intervention values. Changes in pain, self-efficacy, and neck muscle fatigue were retained at the second post-test and tended to be correlated with one another. CONCLUSIONS: Group AT classes may provide a cost-effective approach to reducing neck pain by teaching participants to decrease excessive habitual muscle contraction during everyday activity.

Recovery from Multiple APAs Delays Gait Initiation in Parkinson's Disease.

Background: Freezing of gait in Parkinson's disease (PD) has been linked with deficits in inhibitory control, but causal mechanisms are not established. Freezing at gait initiation (start hesitation) is often accompanied by multiple anticipatory postural adjustments (APAs). If inhibition deficits contribute to freezing by interfering with ability to inhibit initial weight shifts in the wrong direction, then PD subjects should experience more episodes of multiple APAs than healthy controls (HCs) do. If inhibition deficits contribute to freezing by interfering with ability to release a previously inhibited step following multiple APAs, then step onset following multiple APAs should be delayed more in people with PD than in HCs. Methods: Older adults with PD and HC subjects rapidly initiated stepping in response to a light cue in blocks of simple (SRT) and choice (CRT) conditions. We recorded kinematics and ground reaction forces, and we administered the Stroop task to assess inhibitory control. Results: Multiple APAs were more common in CRT than SRT conditions but were equally common in HC and PD subjects. Step onsets were delayed in both conditions and further delayed in trials with multiple APAs, except for HC subjects in SRT trials. Poor Stroop performance correlated with many multiple APAs, late step onset, and rearward position of center of mass (COM) at cue presentation. Forward motion of the COM during the APA was higher in trials with multiple APAs than in trials with single APAs, especially in CRT trials and in PD subjects without self-reported freezing. Conclusion: Start hesitation is not caused by multiple APAs per se, but may be associated with difficulty recovering from multiple APAs, due to difficulty releasing a previously inhibited step.

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.

The clinical significance of freezing while turning in Parkinson's disease.

Freezing of gait (FoG) in people with Parkinson's disease (PD) is an environmentally sensitive, intermittent problem that occurs most often during turning. FoG is difficult for clinicians to evaluate and treat because it can be difficult to elicit during a clinical visit. Here, we aimed to develop a clinically valid objective measure of freezing severity during a 2-min 360-degree turning-in-place. Twenty-eight subjects with PD (16 freezers, FoG+, and 12 nonfreezers, FoG-) in the "off" state and 14 healthy control subjects were tested. Subjects wore three inertial sensors (one on each shin and one on the waist) while (1) turning in place for 2 min (alternating 360 degrees to the right with 360 degrees to the left) and (2) performing an Instrumented 7-m Timed Up and Go test (ITUG). Performance was videotaped, and clinical severity of FoG was independently rated by two movement disorders specialists (co-authors). Turning in place consistently resulted in FoG (13 out of 16 subjects with PD) while FoG was clinically observed in only two subjects with PD during the ITUG test. The Freezing Ratio during the turning test was significantly correlated with the clinical ratings (ρ=0.7, p=0.003) and with score on the new FoG questionnaire (ρ=0.5, p=0.03). After correcting for symptom severity (UPDRS-III), out of the four objective measures of the turning test (total number of turns, average turn peak speed and average turn smoothness), only the Freezing Ratio was significantly different across groups (p=0.04). Freezing can be well quantified with body-worn inertial sensors during a 2-min turning-in-place protocol.

Mobility and Upright Posture Are Associated with Different Aspects of Cognition in Older Adults.

Objectives: Aging is associated with cognitive decline, including visuomotor and memory concerns, and with motor system changes, including gait slowing and stooped posture. We investigated the associations of visuomotor performance and episodic memory with motor system characteristics in healthy older adults. Methods: Neurologically healthy older adults (N = 160, aged 50-89) completed a battery of cognitive and motor tasks. Cognitive variables were grouped by principal components analysis (PCA) into two components: visuomotor performance and verbal episodic memory. Our primary predictor variables were two aspects of motor function: timed-up-and-go (TUG) speed and neck angle. Additional predictor variables included demographic factors (age, sex and education) and indicators of physical fitness (body mass index/BMI and grip strength). All seven predictor variables were entered stepwise into a multiple regression model for each cognitive component. Results: Poor visuomotor performance was best predicted by a combination of advanced age, high BMI and slow TUG, whereas poor verbal memory performance was best predicted by a combination of advanced age, male sex, low education and acute neck angle. Conclusions: Upright posture and mobility were associated with different cognitive processes, suggesting different underlying neural mechanisms. These results provide the first evidence for a link between postural alignment and cognitive functioning in healthy older adults. Possible causal relationships are discussed.

Cognitive Contributions to Freezing of Gait in Parkinson Disease: Implications for Physical Rehabilitation.

People with Parkinson disease (PD) who show freezing of gait also have dysfunction in cognitive domains that interact with mobility. Specifically, freezing of gait is associated with executive dysfunction involving response inhibition, divided attention or switching attention, and visuospatial function. The neural control impairments leading to freezing of gait have recently been attributed to higher-level, executive and attentional cortical processes involved in coordinating posture and gait rather than to lower-level, sensorimotor impairments. To date, rehabilitation for freezing of gait primarily has focused on compensatory mobility training to overcome freezing events, such as sensory cueing and voluntary step planning. Recently, a few interventions have focused on restitutive, rather than compensatory, therapy. Given the documented impairments in executive function specific to patients with PD who freeze and increasing evidence of overlap between cognitive and motor function, incorporating cognitive challenges with mobility training may have important benefits for patients with freezing of gait. Thus, a novel theoretical framework is proposed for exercise interventions that jointly address both the specific cognitive and mobility challenges of people with PD who freeze.

Lighten Up: Specific Postural Instructions Affect Axial Rigidity and Step Initiation in Patients With Parkinson's Disease.

BACKGROUND: Parkinson's disease (PD) is associated with stooped postural alignment, increased postural sway, and reduced mobility. The Alexander Technique (AT) is a mindfulness-based approach to improving posture and mobility by reducing muscular interference while maintaining upward intentions. Evidence suggests that AT can reduce disability associated with PD, but a mechanism for this effect has not yet been established. OBJECTIVE: We investigated whether AT-based instructions reduce axial rigidity and increase upright postural alignment, and whether these instructions have different effects on postural alignment, axial rigidity, postural sway, and mobility than effort-based instructions regarding posture. METHOD: Twenty subjects with PD practiced 2 sets of instructions and then attempted to implement both approaches (as well as a relaxed control condition) during quiet standing and step initiation. The "Lighten Up" instructions relied on AT principles of reducing excess tension while encouraging length. The "Pull Up" instructions relied on popular concepts of effortful posture correction. We measured kinematics, resistance to axial rotation, and ground reaction forces. RESULTS: Both sets of experimental instructions led to increases in upright postural alignment relative to the control condition. Only the Lighten Up instructions led to reduced postural sway, reduced axial postural tone, greater modifiability of tone, and a smoother center of pressure trajectory during step initiation, possibly indicating greater movement efficiency. CONCLUSION: Mindful movement approaches such as AT may benefit balance and mobility in subjects with PD by acutely facilitating increased upright postural alignment while decreasing rigidity.

Dual-task interference and brain structural connectivity in people with Parkinson's disease who freeze.

BACKGROUND: Freezing of gait in people with Parkinson's disease (PD) is likely related to attentional control (ie, ability to divide and switch attention). However, the neural pathophysiology of altered attentional control in individuals with PD who freeze is unknown. Structural connectivity of the pedunculopontine nucleus has been related to freezing and may play a role in altered attentional control; however, this relationship has not been investigated. We measured whether dual-task interference, defined as the reduction in gait performance during dual-task walking, is more pronounced in individuals with PD who freeze, and whether dual-task interference is associated with structural connectivity and/or executive function in this population. METHODS: We measured stride length in 13 people with PD with and 12 without freezing of gait during normal and dual-task walking. We also assessed asymmetry of pedunculopontine nucleus structural connectivity via diffusion tensor imaging and performance on cognitive tests assessing inhibition and set-shifting, cognitive domains related to freezing. RESULTS: Although stride length was not different across groups, change in stride length between normal and dual-task gait (ie, dual-task interference) was more pronounced in people with PD who freeze compared to non-freezers. Further, in people with PD who freeze, dual-task interference was correlated with asymmetry of pedunculopontine nucleus structural connectivity, Go-NoGo target accuracy (ability to release a response) and simple reaction time. CONCLUSIONS: These results support the hypothesis that freezing is related to altered attentional control during gait, and suggest that differences in pedunculopontine nucleus connectivity contribute to poorer attentional control in people with PD who freeze.

Functional reorganization of the locomotor network in Parkinson patients with freezing of gait.

Freezing of gait (FoG) is a transient inability to initiate or maintain stepping that often accompanies advanced Parkinson's disease (PD) and significantly impairs mobility. The current study uses a multimodal neuroimaging approach to assess differences in the functional and structural locomotor neural network in PD patients with and without FoG and relates these findings to measures of FoG severity. Twenty-six PD patients and fifteen age-matched controls underwent resting-state functional magnetic resonance imaging and diffusion tensor imaging along with self-reported and clinical assessments of FoG. After stringent movement correction, fifteen PD patients and fourteen control participants were available for analysis. We assessed functional connectivity strength between the supplementary motor area (SMA) and the following locomotor hubs: 1) subthalamic nucleus (STN), 2) mesencephalic and 3) cerebellar locomotor region (MLR and CLR, respectively) within each hemisphere. Additionally, we quantified structural connectivity strength between locomotor hubs and assessed relationships with metrics of FoG. FoG+ patients showed greater functional connectivity between the SMA and bilateral MLR and between the SMA and left CLR compared to both FoG- and controls. Importantly, greater functional connectivity between the SMA and MLR was positively correlated with i) clinical, ii) self-reported and iii) objective ratings of freezing severity in FoG+, potentially reflecting a maladaptive neural compensation. The current findings demonstrate a re-organization of functional communication within the locomotor network in FoG+ patients whereby the higher-order motor cortex (SMA) responsible for gait initiation communicates with the MLR and CLR to a greater extent than in FoG- patients and controls. The observed pattern of altered connectivity in FoG+ may indicate a failed attempt by the CNS to compensate for the loss of connectivity between the STN and SMA and may reflect a loss of lower-order, automatic control of gait by the basal ganglia.

Inhibition, executive function, and freezing of gait.

BACKGROUND: Studies suggest that freezing of gait (FoG) in people with Parkinson's disease (PD) is associated with declines in executive function (EF). However, EF is multi-faceted, including three dissociable components: inhibiting prepotent responses, switching between task sets, and updating working memory. OBJECTIVE: This study investigated which aspect of EF is most strongly associated with FoG in PD. METHOD: Three groups were studied: adults with PD (with and without FoG) and age-matched, healthy adults. All participants completed a battery of cognitive tasks previously shown to discriminate among the three EF components. Participants also completed a turning-in-place task that was scored for FoG by neurologists blind to subjects' self-reported FoG. RESULTS: Compared to both other groups, participants with FoG showed significant performance deficits in tasks associated with inhibitory control, even after accounting for differences in disease severity, but no significant deficits in task-switching or updating working memory. Surprisingly, the strongest effect was an intermittent tendency of participants with FoG to hesitate, and thus miss the response window, on go trials in the Go-Nogo task. The FoG group also made slower responses in the conflict condition of the Stroop task. Physician-rated FoG scores were correlated both with failures to respond on go trials and with failures to inhibit responses on nogo trials in the Go-Nogo task. CONCLUSION: These results suggest that FoG is associated with a specific inability to appropriately engage and release inhibition, rather than with a general executive deficit.

Protocol to assess the neurophysiology associated with multi-segmental postural coordination.

Anticipatory postural adjustments (APAs) stabilize potential disturbances to posture caused by movement. Impaired APAs are common with disease and injury. Brain functions associated with generating APAs remain uncertain due to a lack of paired tasks that require similar limb motion from similar postural orientations, but differ in eliciting an APA while also being compatible with brain imaging techniques (e.g., functional magnetic resonance imaging; fMRI). This study developed fMRI-compatible tasks differentiated by the presence or absence of APAs during leg movement. Eighteen healthy subjects performed two leg movement tasks, supported leg raise (SLR) and unsupported leg raise (ULR), to elicit isolated limb motion (no APA) versus multi-segmental coordination patterns (including APA), respectively. Ground reaction forces under the feet and electromyographic activation amplitudes were assessed to determine the coordination strategy elicited for each task. Results demonstrated that the ULR task elicited a multi-segmental coordination that was either minimized or absent in the SLR task, indicating that it would serve as an adequate control task for fMRI protocols. A pilot study with a single subject performing each task in an MRI scanner demonstrated minimal head movement in both tasks and brain activation patterns consistent with an isolated limb movement for the SLR task versus multi-segmental postural coordination for the ULR task.

Asymmetric pedunculopontine network connectivity in parkinsonian patients with freezing of gait.

Freezing of gait is one of the most debilitating symptoms in Parkinson's disease as it causes falls and reduces mobility and quality of life. The pedunculopontine nucleus is one of the major nuclei of the mesencephalic locomotor region and has neurons related to anticipatory postural adjustments preceding step initiation as well as to the step itself, thus it may be critical for coupling posture and gait to avoid freezing. Because freezing of gait and postural impairments have been related to frontal lesions and frontal dysfunction such as executive function, we hypothesized that freezing is associated with disrupted connectivity between midbrain locomotor regions and medial frontal cortex. We used diffusion tensor imaging to quantify structural connectivity of the pedunculopontine nucleus in patients with Parkinson's disease with freezing of gait, without freezing, and healthy age-matched controls. We also included behavioural tasks to gauge severity of freezing of gait, quantify gait metrics, and assess executive cognitive functions to determine whether between-group differences in executive dysfunction were related to pedunculopontine nucleus structural network connectivity. Using seed regions from the pedunculopontine nucleus, we were able to delineate white matter connections between the spinal cord, cerebellum, pedunculopontine nucleus, subcortical and frontal/prefrontal cortical regions. The current study is the first to demonstrate differences in structural connectivity of the identified locomotor pathway in patients with freezing of gait. We report reduced connectivity of the pedunculopontine nucleus with the cerebellum, thalamus and multiple regions of the frontal cortex. Moreover, these structural differences were observed solely in the right hemisphere of patients with freezing of gait. Finally, we show that the more left hemisphere-lateralized the pedunculopontine nucleus tract volume, the poorer the performance on cognitive tasks requiring the initiation of appropriate actions and/or the inhibition of inappropriate actions, specifically within patients with freezing. These results support the notion that freezing of gait is strongly related to structural deficits in the right hemisphere's locomotor network involving prefrontal cortical areas involved in executive inhibition function.

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.