Changes In Movement Amplitude Research Articles

Deep brain stimulation in the subthalamic nuclei alters postural alignment and adaptation in Parkinson's disease.

Parkinson’s disease (PD) can produce postural abnormalities of the standing body position such as kyphosis. We investigated the effects of PD, deep brain stimulation (DBS) in the subthalamic nucleus (STN), vision and adaptation on body position in a well-defined group of patients with PD in quiet standing and during balance perturbations. Ten patients with PD and 25 young and 17 old control participants were recruited. Body position was measured with 3D motion tracking of the ankle, knee, hip, shoulder and head. By taking the ankle as reference, we mapped the position of the joints during quiet standing and balance perturbations through repeated calf muscle vibration. We did this to explore the effect of PD, DBS in the STN, and vision on the motor learning process of adaptation in response to the repeated stimulus. We found that patients with PD adopt a different body position with DBS ON vs. DBS OFF, to young and old controls, and with eyes open vs. eyes closed. There was an altered body position in PD with greater flexion of the head, shoulder and knee (p≤0.042) and a posterior position of the hip with DBS OFF (p≤0.014). With DBS ON, body position was brought more in line with the position taken by control participants but there was still evidence of greater flexion at the head, shoulder and knee. The amplitude of movement during the vibration period decreased in controls at all measured sites with eyes open and closed (except at the head in old controls with eyes open) showing adaptation which contrasted the weaker adaptive responses in patients with PD. Our findings suggest that alterations of posture and greater forward leaning with repeated calf vibration, are independent from reduced movement amplitude changes. DBS in the STN can significantly improve body position in PD although the effects are not completely reversed. Patients with PD maintain adaptive capabilities by leaning further forward and reducing movement amplitude despite their kyphotic posture.

Virtual Reality in Fibromyalgia: Does Altering Visual Feedback Impact on Pain and Movement During Reaching?

People with fibromyalgia (FM) have movement-related fear impacting on daily activities. While virtual reality has been used as a distractor to promote exercise, it can be used to manipulate visual feedback (VF) about movement, potentially influencing pain and movement. Objectives: A. To determine whether altered VF modulates pain during movement; B. To compare adaptation to an altered VF between FM participants and healthy controls (HC); C. To explore relationships between adaptation, limb position sense, kinesiophobia and pain. 20 FM participants and 20 HC performed a reaching task during two sessions in a KINARM exoskeleton including a virtual reality interface allowing to replace their arm with a virtual arm. In one session, VF was altered to show GREATER movements while in the other it showed SMALLER movements (randomized order). Pain was assessed periodically using a numerical rating scale. Movement amplitude was assessed during exposure to altered VF (adaptation) and pre-/post-exposure (without VF; after-effects). Limb position sense was assessed with a KINARM task, and kinesiophobia was assessed with the Tampa Scale for Kinesiophobia (TSK-11). Pain intensity increased slightly with movement repetitions (p < 0.001), but did not differ between the VF conditions (GREATER vs. SMALLER). Both groups exhibited visuomotor adaptation, as shown by VF-dependent changes in movement amplitude and speed during exposure to altered VF, and by the presence of VF-dependent after-effects (p < 0.001 for all variables). However, no differences were observed across groups for any of these variables, despite the fact that FM had significantly more difficulty to correctly detect VF conditions than HC (p = 0.046). No clear limb position sense deficits were observed in FM participants, and no significant relationships were found between TSK-11 scores and changes in pain intensity during exposure to altered VF. Altering VF did not influence pain during a reaching task in the FM group. Surprisingly, both groups adapted similarly to altered VF. Visuomotor adaptation is therefore preserved in FM, despite impairments in sensory perception and the poor ability to detect VF alterations in the present study. Further research is warranted to clarify the relationship between sensory perceptions and motor control in FM.

Repetitive Finger Movement and Dexterity Tasks in People With Parkinson's Disease.

Little is known regarding how repetitive finger movement performance, an assessment of bradykinesia (slowness of movement), is related to fine-motor dexterity tasks in people with Parkinson's disease (PD). This pilot study examined the relationship between the performance of fine-motor dexterity tasks and repetitive finger movement in people with PD. Forty-six participants with PD completed an acoustically cued repetitive finger movement task (1-3 Hz). Movement amplitude, movement rate difference, and coefficient of variation were obtained for each tone rate. Participants also completed a buttoning and Purdue pegboard assembly task. Buttoning time and number of assemblies were recorded. A significant association was found between movement rate difference and movement rate difference coefficient of variation and buttoning performance in which higher movement rate and higher variability were associated with slower buttoning times. No significant associations between any of the repetitive finger movement outcome measures and Purdue pegboard assembly performance were revealed. Changes in movement amplitude and movement rate may influence fine-motor dexterity tasks differently. Thus, it is important to consider the quantitative assessment of both movement rate and movement amplitude because they may indicate differential clinical applications in the treatment of people with PD.

Timing of motor cortical stimulation during planar robotic training differentially impacts neuroplasticity in older adults

ObjectiveThe objective was to determine how stimulation timing applied during reaching influenced neuroplasticity related to practice. Older adult participants were studied to increase relevance for stroke rehabilitation and aging. MethodsSixteen participants completed 3 sessions of a reaching intervention with 480 planar robotic movement trials. Sub-threshold, single-pulse transcranial magnetic stimulations (TMS) were delivered during the late reaction time (LRT) period, when muscle activity exceeded a threshold (EMG-triggered), or randomly. Assessments included motor evoked potentials (MEP), amplitude, and direction of supra-threshold TMS-evoked movements and were calculated as change scores from baseline. ResultsThe direction of TMS-evoked movements significantly changed after reaching practice (p<0.05), but was not significantly different between conditions. Movement amplitude changes were significantly different between conditions (p<0.05), with significant increases following the LRT and random conditions. MEP for elbow extensors and flexors, and the shoulder muscle that opposed the practice movement were significantly different between conditions with positive changes following LRT, negative changes following EMG-triggered, and no changes following the random condition. Motor performance including movement time and peak velocity significantly improved following the training but did not differ between conditions. ConclusionsThe responsiveness of the motor cortex to stimulation was affected positively by stimulation during the late motor response period and negatively during the early movement period, when stimulation was combined with robotic reach practice. SignificanceThe sensitivity of the activated motor cortex to additional stimulation is highly dynamic.

Generalization of Dynamics Learning Across Changes in Movement Amplitude

Studies on generalization show the nature of how learning is encoded in the brain. Previous studies have shown rather limited generalization of dynamics learning across changes in movement direction, a finding that is consistent with the idea that learning is primarily local. In contrast, studies show a broader pattern of generalization across changes in movement amplitude, suggesting a more general form of learning. To understand this difference, we performed an experiment in which subjects held a robotic manipulandum and made movements to targets along the body midline. Subjects were trained in a velocity-dependent force field while moving to a 15 cm target. After training, subjects were tested for generalization using movements to a 30 cm target. We used force channels in conjunction with movements to the 30 cm target to assess the extent of generalization. Force channels restricted lateral movements and allowed us to measure force production during generalization. We compared actual lateral forces to the forces expected if dynamics learning generalized fully. We found that, during the test for generalization, subjects produced reliably less force than expected. Force production was appropriate for the portion of the transfer movement in which velocities corresponded to those experienced with the 15 cm target. Subjects failed to produce the expected forces when velocities exceeded those experienced in the training task. This suggests that dynamics learning generalizes little beyond the range of one's experience. Consistent with this result, subjects who trained on the 30 cm target showed full generalization to the 15 cm target. We performed two additional experiments that show that interleaved trials to the 30 cm target during training on the 15 cm target can resolve the difference between the current results and those reported previously.

Response preparation changes following practice of an asymmetrical bimanual movement

The purpose of the current study was to examine the effects of practice on the advance preparation of an asymmetrical bimanual movement. Participants performed 170 trials of a discrete bimanual aiming movement where the right arm moved twice the amplitude of the left, in response to an auditory "go" signal. During three of the first and last ten trials, the "go" signal was replaced with a startle (124 dB) stimulus, which is thought to trigger a prepared movement. Startle and non-startle (control) trials from early and late practice were compared on various kinematic and EMG measures. Results indicated that it is possible to pre-program a bimanual asymmetrical movement, and that advance preparation of movement amplitude changes with practice. Evidence was also provided that the different amplitude movements were performed using similar EMG timing between limbs, while adjusting the relative ratio of EMG amplitude. Furthermore, learning of the task appeared to be related to the ability to prepare the correct asymmetrical EMG amplitudes rather than changing the timing of the EMG pattern.

Interval timing and trajectory in unequal amplitude movements

The Wing-Kristofferson (WK) model of movement timing emphasises the separation of central timer and motor processes. Several studies of repetitive timing have shown that increase in variability at longer intervals is attributable to timer processes; however, relatively little is known about the way motor aspects of timing are affected by task movement constraints. In the present study, we examined timing variability in finger tapping with differences in interval to assess central timer effects, and with differences in movement amplitude to assess motor implementation effects. Then, we investigated whether effects of motor timing observed at the point of response (flexion offset/tap) are also evident in extension, which would suggest that both phases are subject to timing control. Eleven participants performed bimanual simultaneous tapping, at two target intervals (400, 600 ms) with the index finger of each hand performing movements of equal (3 or 6 cm) or unequal amplitude (left hand 3, right hand 6 cm and vice versa). As expected, timer variability increased with the mean interval but showed only small, non-systematic effects with changes in movement amplitude. Motor implementation variability was greater in unequal amplitude conditions. The same pattern of motor variability was observed both at flexion and extension phases of movement. These results suggest that intervals are generated by a central timer, triggering a series of events at the motor output level including flexion and the following extension, which are explicitly represented in the timing system.

Age-related changes in upper body adaptation to walking speed in human locomotion

Assessments of changes in gait stability due to aging and disease are predominantly based on lower extremity kinematic and kinetic data. These gait changes are also often based on comparisons at preferred speed only. The purpose of this experiment was to: (1) examine age-related changes in range of motion and coordination of segments of the upper body during locomotion; and (2) investigate the effects of a systematic walking velocity manipulation on rotational motion and coordination. Participants (n=30) walked on a motor driven treadmill at speeds ranging from 0.2 to 1.8m/s and were divided into three groups with mean ages of 23.3, 49.3 and 72.6 years, respectively. Seven high-speed infrared cameras were used to record three-dimensional kinematics of the pelvis, trunk and head. Dependent variables were amplitude of segmental and joint rotations, as well as relative phase to assess coordination between segments. Although no differences in stride parameters were found between the groups, age-related changes in movement amplitude in response to speed manipulations were observed for all segments and joints. Pelvic rotations in sagittal, frontal and transverse planes of motion were systematically reduced with age. Older individuals showed reduced trunk flexion-extension in the sagittal plane and increased trunk axial rotation in the transverse plane. Coordination analysis showed reduced compensatory movement between pelvis and trunk in older individuals. These findings support the importance of systematic manipulation of walking velocity and three-dimensional upper body kinematics in assessing age-related changes in locomotor stability and adaptability.

Cerebellum-dependent learning: the role of multiple plasticity mechanisms.

The cerebellum is an evolutionarily conserved structure critical for motor learning in vertebrates. The model that has influenced much of the work in the field for the past 30 years suggests that motor learning is mediated by a single plasticity mechanism in the cerebellum: long-term depression (LTD) of parallel fiber synapses onto Purkinje cells. However, recent studies of simple behaviors such as the vestibulo-ocular reflex (VOR) indicate that multiple plasticity mechanisms contribute to cerebellum-dependent learning. Multiple plasticity mechanisms may provide the flexibility required to store memories over different timescales, regulate the dynamics of movement, and allow bidirectional changes in movement amplitude. These plasticity mechanisms must act in combination with appropriate information-coding strategies to equip motor-learning systems with the ability to express learning in correct contexts. Studies of the patterns of generalization of motor learning in the VOR provide insight about the coding of information in neurons at sites of plasticity. These principles emerging from studies of the VOR are consistent with results concerning more complex behaviors and thus may reflect general principles of cerebellar function.

Movement amplitude and tempo change in piano performance

Music performance places stringent temporal and cognitive demands on individuals that should yield large speed/accuracy tradeoffs. Skilled piano performance, however, shows consistently high accuracy across a wide variety of rates. Movement amplitude may affect the speed/accuracy tradeoff, so that high accuracy can be obtained even at very fast tempi. The contribution of movement amplitude changes in rate (tempo) is investigated with motion capture. Cameras recorded pianists with passive markers on hands and fingers, who performed on an electronic (MIDI) keyboard. Pianists performed short melodies at faster and faster tempi until they made errors (altering the speed/accuracy function). Variability of finger movements in the three motion planes indicated most change in the plane perpendicular to the keyboard across tempi. Surprisingly, peak amplitudes of motion before striking the keys increased as tempo increased. Increased movement amplitudes at faster rates may reduce or compensate for speed/accuracy tradeoffs. [Work supported by Canada Research Chairs program, HIMH R01 45764.]

Gait transitions during unrestrained locomotion in dogs.

Gait transitions during long distance, unrestrained locomotion were studied in 22 mongrel dogs. Spatial and temporal limb movement parameters were collected and the phase relationships between limb movements based upon a 2-dimensional (2-D) gait diagram were computed. During most of the trials, the dogs trotted within a relatively narrow velocity range. Gait transitions were observed during radical changes of the movement velocity. In most cases the gait switches were abrupt and completed within 2 strides of the gait cycle. The dogs walked, depending on the animal size, within the upper velocity range of 0.93-1.21 m/s. Most of the walk-trot transitions were observed within this range. All of them had a typical pattern that involved changes of the phase shift between diagonal limb movements from 0.31 +/- 0.02 (a typical value for a walking dog) down to 0.02 +/- 0.03. These changes appeared abruptly within one stride cycle for each diagonal pair of limbs; therefore, the transition was completed in 2 strides of the gait cycle. The switch involved momentary shortening of the hindlimb amplitudes. During the next gait cycle, all limb movement amplitudes were reduced with a concomitant increase in limb movement frequencies. In contrast to the clear border between the symmetrical gaits, the dogs switched to gallop at any speed within the trot range (most frequently between 1.5-2.6 m/s). The transitions were usually completed within one stride of the diagonal limbs. In most cases, the switch from trot to gallop had a similar pattern; while maintaining synchronous movement of one diagonal pair of limbs, the other pair movement control was modified accordingly. The typical transition pattern involved the shortening of the swing phase in the front limb with simultaneous lengthening of the swing phase in the diagonal hindlimb. These transient modifications had their equivalent in the analogous limb movement amplitude changes. A mirror-image pattern of phase changes was observed in the majority (82%) of the gallop-trot transitions. Three of the dogs, however, besides the typical gallop-trot switch, occasionally employed a second pattern of transition.

Prehension With the Ipsilesional Hand After Unilateral Brain Damage

Sensorimotor deficits in the hand ipsilateral to a brain lesion have been reported in different motor tasks. We evaluated performance of the ipsilesional hand in 12 patients with either left (LBD) or right brain damage (RBD) by kinematic analysis in order to precisely characterize possible deficits in the two components of prehension (transport and grasp). Both patient groups exhibited performance deficits in the main kinematic parameters, e.g., reduced velocity of the transport component and prolonged movement time. However, while LBD patients showed a more general slowing, RBD patients prolonged in particular the last phase of the movement toward the object. We suggest that relevant visuospatial representations and the adequate mapping of motor processes may be impaired after RBD. In contrast, LBD caused a more unspecific disturbance pattern, supporting the view that the precise parameterization of motor programs is impaired. Maximum grip aperture was normal in both patient groups. However, since aperture could be biased by slowed movement, the notion that the grasp component was preserved remains speculative. The patient's ability to scale the maximum velocity of the transport component to adapt to changes in movement amplitude and to scale the maximum hand aperture of the grasp component to adapt to object size was preserved in both groups. Thus both hemispheres can have competence for this scaling mechanism.

Parkinsonian arm movements as altered by task difficulty

A discrete elbow movement to targets with different indexes of difficulty (ID) was used to determine the kinematic organization of arm movements in a young, an elderly and a Parkinson's disease (PD) group (n = 14). Target size and movement amplitude changes led to expected modifications of the kinematics in all three groups according to Fitts' law. Increased task demands by changing target size produced not only differences between the age-groups, but affected the modulation of velocity and acceleration in the parkinsonian patients differentially. For large amplitude movements, the PD patients were less able to increase velocity and acceleration magnitudes when target accuracy constraints were reduced. These findings, when taken together with the observation that speed scaling was preserved for small movement amplitudes, suggest that a reduced capability to initiate and regulate force is the cause for the observed slowness in PD.

The equilibrium point hypothesis and its application to speech motor control.

In this paper, we address a number of issues in speech research in the context of the equilibrium point hypothesis of motor control. The hypothesis suggests that movements arise from shifts in the equilibrium position of the limb or the speech articulator. The equilibrium is a consequence of the interaction of central neural commands, reflex mechanisms, muscle properties, and external loads, but it is under the control of central neural commands. These commands act to shift the equilibrium via centrally specified signals acting at the level of the motoneurone (MN) pool. In the context of a model of sagittal plane jaw and hyoid motion based on the lambda version of the equilibrium point hypothesis, we consider the implications of this hypothesis for the notion of articulatory targets. We suggest that simple linear control signals may underlie smooth articulatory trajectories. We explore as well the phenomenon of intraarticulator coarticulation in jaw movement. We suggest that even when no account is taken of upcoming context, that apparent anticipatory changes in movement amplitude and duration may arise due to dynamics. We also present a number of simulations that show in different ways how variability in measured kinematics can arise in spite of constant magnitude speech control signals.

Rapid movements with reversals in direction. II. Control of movement amplitude and inertial load.

Transformations of the underlying movement control of rapid sequential (reversal) responses were examined as the movement amplitude (Experiment 1) and moment of inertia (Experiment 2) were altered, with constant movement time. Increases in amplitude and inertia were both met by sharply increased joint torques with a constant temporal structure, suggesting that the alterations may have been governed by a single gain parameter. The durations of various EMG bursts were essentially constant across changes in inertia, supporting a model in which the output of a fixed temporal representation is amplified to alter joint torques. The EMG amplitudes increased greatly with both amplitude and load. However, the fact that the EMG durations increased systematically with increases in distance provided difficulties for this model of amplitude control. The data suggest an economy in motor control in simple agravitational movements, whereby relatively simple transformations of an underlying representation can accommodate large changes in movement amplitude and moment of inertia.