Lesley A. Brown

Central set influences on gait. Age-dependent effects of postural threat.

We tested the hypothesis that anxiety regarding the potential consequences of a possible fall would alter gait patterns differently between younger and older adults. Sixteen younger and fifteen older adults participated in this study. Participants walked at a selfdetermined velocity along a 7.2-m walkway under 4 different conditions of postural threat; the walking conditions varied depending on the width constraints of the walkway (0.60 m vs 0.15 m) and the height of the walking surface (floor vs elevated: 0 m vs 0.60 m). Results indicated that although both younger and older adults altered their gait patterns under conditions of increased postural threat, the movement adaptations observed among older adults were substantially different to those adopted by younger adults. These age-dependent differences were strongly evidenced in the joint kinematics and the variability of the gait pattern within each condition. Our findings also indicated that when postural threat increased, the level of muscle activation throughout the gait cycle was altered in the distal musculature (gastrocnemius m. and tibialis anterior m.) among older adults only. Based on the age-related differences observed, we believe that the gait pattern alterations observed among younger and older adults reflect central set modifications to postural control that are mediated by a heightened anxiety imposed by the constraints of the testing conditions. Based on the age-dependent differences in the observed gait pattern modifications, it appears that the effects of anxiety on the control of locomotion are more pervasive for older adults than for younger adults.

Walking with music is a safe and viable tool for gait training in Parkinson's disease: the effect of a 13-week feasibility study on single and dual task walking

This study explored the viability and efficacy of integrating cadence-matched, salient music into a walking intervention for patients with Parkinsons disease (PD). Twenty-two people with PD were randomised to a control (CTRL, n = 11) or experimental (MUSIC, n = 11) group. MUSIC subjects walked with an individualised music playlist three times a week for the intervention period. Playlists were designed to meet subjects musical preferences. In addition, the tempo of the music closely matched (±10–15 bpm) the subjects preferred cadence. CTRL subjects continued with their regular activities during the intervention. The effects of training accompanied by “walking songs” were evaluated using objective measures of gait score. The MUSIC group improved gait velocity, stride time, cadence, and motor symptom severity following the intervention. This is the first study to demonstrate that music listening can be safely implemented amongst PD patients during home exercise.

Compensatory stepping : The biomechanics of a preferred response among older adults

Abstract The purpose of this study was to evaluate age-related differences in the mechanics of the compensatory stepping response to balance threats. A moving platform was used to disturb the balance of 16 younger (21 to 35 years) and 19 older (68 to 88 years) adults. Backward platform translations consisted of 15-cm displacements with peak accelerations ranging from 9.4 to 15.2 m/s2. Older adults were more likely to use a step to recover balance and stepped at lower perturbation magnitudes than younger adults. Group differences were not found in time to step initiation or segmental momentum. The lack of group differences in momentum revealed that lower perturbation accelerations created an equivalent or greater magnitude of body motion in older adults compared to higher accelerations experienced by younger adults. Older adults also showed a reduced ability to attenuate the input acceleration and experienced significantly greater linear acceleration of the head.

The translating platform paradigm: perturbation displacement waveform alters the postural response

The translating platform paradigm is widely used to investigate the regulation of upright standing and locomotion. This study investigated how the displacement waveform characteristics underlying the translating platform perturbation are revealed in the resulting postural response. Eight participants experienced a series of backward-directed perturbations using a hydraulically driven forceplate. Two ranges of platform displacement (5 and 15 cm) in combination with two peak velocities (40 and 60 cm/s) were achieved using three distinct waveforms for platform displacement: (a) RAMP: ramp onset and ramp offset, (b) Ramp-to-Parabola (R-P): ramp onset with parabolic offset and (c) SINE: sine-wave onset with sine wave offset. Our findings indicated that the unique and distinctive acceleration and deceleration characteristics that result from the three different platform displacement waveforms significantly altered the postural response to the perturbation.

Obstacle negotiation kinematics: age-dependent effects of postural threat

This study investigated whether obstacle negotiation kinematics among younger (YA) and older adults (OA) are influenced by postural threat. Obstacle negotiation kinematics among YA and OA were examined under four conditions of postural threat. Seventeen older and 15 YA negotiated a fixed virtual obstacle while walking at a self-determined velocity along a 7.2 m walkway. Postural threat was manipulated by varying the width (0.60 vs. 0.15 m) and height (0.00 vs. 0.60 m) of the walkway. Increasing postural threat resulted in elevated levels of physiological arousal and altered crossing kinematics for all subjects. Specifically, crossing step length, lead limb velocity, trail limb velocity, and whole body center of mass (COM) velocity decreased and lead limb crossing height increased in the condition of greatest postural threat compared with the condition of least postural threat. Although both YA and OA altered obstacle negotiation kinematics under conditions of postural threat, the changes observed among older adults were considerably different from those of YA. In particular, OA demonstrated more marked reductions in the crossing velocity of the lead limb, trail limb, and COM than YA between the condition of least postural threat and the condition of greatest postural threat. The results of this study reveal that postural threat influences negotiation kinematics among YA and OA and illustrate that age-dependent differences exist for obstacle negotiation kinematics when postural threat increases. These findings may imply a beneficial effect of fear of falling on reducing fall probability among healthy OA.

Novel Challenges to Gait in Parkinson's Disease: The Effect of Concurrent Music in Single- and Dual-Task Contexts

OBJECTIVE To investigate the effect of concurrent music on parkinsonian gait in single- and dual-task contexts. DESIGN A counterbalanced repeated-measure design. SETTING A university balance research laboratory. PARTICIPANTS People with idiopathic Parkinsons disease (PD) (n=10) (67+/-7 y) and healthy age-matched (65+/-6 y) control subjects (n=10). INTERVENTION Subjects walked at a self-selected pace along an unobstructed walkway in 4 differing test conditions. Test conditions were differentiated by the presence of music accompaniment (no music/music) and the presence of a secondary cognitive task (single/dual). Single- and dual-task conditions were randomized; trials were blocked by the presence of music and counterbalanced between subjects. Music was self-selected by subjects. The cognitive task consisted of serial subtractions (3s). Subjects were not instructed to attend to the music nor were they provided with instructions regarding task prioritization. MAIN OUTCOME MEASURES Mean gait velocity, stride length, and the percentage of the gait cycle spent in double-limb support. RESULTS Gait among the PD patients was adversely affected by concurrent music. In contrast, gait performance in the control subjects showed no significant difference between no music and music conditions. The added requirement of a cognitive task differentially influenced gait performance in PD patients and control subjects, with PD patients displaying a further decrease in spatiotemporal parameters of gait and control subjects displaying a marginal improvement. CONCLUSIONS Gait impairments associated with PD are exacerbated in the presence of concurrent music, an effect that is further exaggerated by the addition of a cognitive task. These results have implications for patient safety in multitasking situations.

Visual Guidance for Hand Advance but Not Hand Withdrawal in a Reach-to-Eat Task in Adult Humans: Reaching Is a Composite Movement

Many animal species use reaching for food to place in the mouth (reach-to-eat) with a hand, and it may be a primitive movement. Although researchers (I. Q. Whishaw, 2005; A. N. Iwaniuk & I. Q. Whishaw, 2000; M. Gentiluci, I. Toni, S. Chieffi, & G. Pavesi, 1994) have described visual guidance of reaching in both normal and brain-injured human and nonhuman primates, researchers have not described the contribution of vision during advance of the limb to grasp food and during withdrawal of the limb with food to the mouth. To evaluate visual contributions, the authors monitored eye movements in young adults as they reached for food with and without vision. Participants visually engaged the target prior to the 1st hand movement and disengaged it as the food was grasped. Visual occlusion slowed limb advance and altered digit shaping but did not affect withdrawal. The dependence on visual control of advance but not withdrawal suggests that the reach-to-eat movement is a composite of 2 basic movements under visual and tactile/proprioceptive guidance, respectively.

Pallidal deep brain stimulation and L-dopa do not improve qualitative aspects of skilled reaching in Parkinson's disease.

OBJECTIVE To determine effects of dopaminergic medication and pallidal deep brain stimulation (DBS) on skilled reach in Parkinsons disease (PD). BACKGROUND PD is a neurodegenerative disorder affecting motor control. While speed and execution of movements are improved by L-dopa, not all motor symptoms are alleviated. Little is known about the effects of DBS or medication on reaching. DESIGN METHOD Eight PD patients with unilateral pallidal DBS reached with the contra-lateral hand for a piece of food, placing it in the mouth, and returning to starting position. Testing was performed on no treatment, medication only, DBS only, and combined treatment. Reaches were digitally recorded and analyzed on a 21 point scale adapted from Eshkol-Wachman Notation. Analysis was blinded, with patients compared to age-matched controls. RESULTS Patients were tested 6-13 months after surgery. All showed significant improvement clinically and in UPDRS (III) scores. The following data were obtained on the reaching scale: normal controls 16.5-21.0 (mean 18.3), no treatment 3.0-12.5 (mean 7.4), medication only 7.0-14.0 (mean 10.3), DBS only 4.5-16.0 (mean 9.2), combined treatment 4.0-15.0 (mean 9.5). The difference between controls and all treatment groups was statistically significant (P<0.005). All aspects of reach were compromised. No significant differences were found among the four conditions. CONCLUSIONS This study is consistent with accumulating evidence that some aspects of motor performance in PD patients, such as reaching, are resistant to L-dopa. Also, pallidal DBS does not improve those parameters that are resistant to L-dopa, either alone or in combination with medication.

Motor deficits in Parkinsonian reaching: dopa-sensitivity influenced by real-world task constraint.

Parkinsons disease (PD) patients can perform many daily activities, but movement deficits are evident. Those deficits may be increased when the required movement is constrained in accuracy. Variable improvements in performance with PD medication have been demonstrated, and sensitivity to task constraint has been evident in some studies. The authors quantified both specific movement deficits and improvements for PD patients in a reaching task. PD patients (N = 8) both on and off medication showed a need for greater ongoing control in movements with higher task-accuracy constraints. Increased task-accuracy constraints further compromised movement timing and structure among PD patients who were off medication, suggesting that unmedicated PD patients may typically compensate by using more conscious control of movement, resulting in increased slowing and segmentation of components when higher task accuracy is required.

A new quantitative method for evaluating freezing of gait and dual-attention task deficits in Parkinson's disease.

People with Parkinson’s disease (PD) can exhibit disabling gait symptoms such as freezing of gait especially when distracted by a secondary task. Quantitative measurement method of this type of cognitive–motor abnormality, however, remains poorly developed. Here we examined whether stepping-in-place (SIP) with a concurrent mental task (e.g., subtraction) can be used as a simple method for evaluating cognitive–motor deficits in PD. We used a 4th generation iPod Touch sensor system to capture hip flexion data and obtain step height (SH) measurements (z axis). The accuracy of the method was compared to and validated by kinematic video analysis software. We found a general trend of reduced SH for PD subjects relative to controls under all conditions. However, the SH of PD freezers was significantly worse than PD non-freezers and controls during concurrent serial 7 subtraction and SIP tasking. During serial 7 subtraction, SH was significantly associated with whether or not a PD patient was a self-reported freezer even when controlling for disease severity. Given that this SIP-based dual-task paradigm is not limited by space requirements and can be quantified using a mobile tracking device that delivers specifically designed auditory task instructions, the method reported here may be used to standardize clinical assessment of cognitive–motor deficits under a variety of dual-task conditions in PD.