The use of enhanced intrinsic feedback for motor learning in stroke survivors: Clinical trial protocol.

BACKGROUND: Stroke can lead to lasting sensorimotor deficits of the upper limb (UL) persisting into the chronic phase despite intensive rehabilitation. A major impairment of reaching after stroke is a decreased range of active elbow extension, which in turn leads to the use of compensatory movements. Retraining movement patterns relies on cognition and motor learning principles. Implicit learning may lead to better outcomes than explicit learning. Error augmentation (EA) is a feedback modality based on implicit learning resulting in improved precision and speed of UL reaching movements in people with stroke. However, accompanying changes in UL joint movement patterns have not been investigated. The objective of this study is to determine the capacity for implicit motor learning in people with chronic stroke and how this capacity is affected by post-stroke cognitive impairments. METHODS: Fifty-two subjects who have chronic stroke will practice reaching movements 3×/wk. for 9 wk. in a virtual reality environment. Participants will be randomly allocated to 1 of 2 groups to train with or without EA feedback. Outcome measures (pre-, post- and follow-up) will be: endpoint precision, speed, smoothness, and straightness and joint (UL and trunk) kinematics during a functional reaching task. The degree of cognitive impairment, lesion profile, and integrity of descending white matter tracts will be related to training outcomes. CONCLUSIONS: The results will inform us which patients can best benefit from training programs that rely on motor learning and utilize enhanced feedback. TRIAL STATUS: Ethical approval for this study was finalized in May 2022. Recruitment and data collection is actively in progress and is planned to finish in 2026. Data analysis and evaluation will occur subsequently, and the final results will be published.

Standardized Measurement of Quality of Upper Limb Movement After Stroke: Consensus-Based Core Recommendations From the Second Stroke Recovery and Rehabilitation Roundtable.

The second Stroke Recovery and Rehabilitation Roundtable "metrics" task force developed consensus around the recognized need to add kinematic and kinetic movement quantification to its core recommendations for standardized measurements of sensorimotor recovery in stroke trials. Specifically, we focused on measurement of the quality of upper limb movement. We agreed that the recommended protocols for measurement should be conceptually rigorous, reliable, valid and responsive to change. The recommended measurement protocols include four performance assays (i.e. 2D planar reaching, finger individuation, grip strength, and precision grip at body function level) and one functional task (3D drinking task at activity level) that address body function and activity respectively. This document describes the criteria for assessment and makes recommendations about the type of technology that should be used for reliable and valid movement capture. Standardization of kinematic measurement protocols will allow pooling of participant data across sites, thereby increasing sample size aiding meta-analyses of published trials, more detailed exploration of recovery profiles, the generation of new research questions with testable hypotheses, and development of new treatment approaches focused on impairment. We urge the clinical and research community to consider adopting these recommendations.

Standardized measurement of quality of upper limb movement after stroke: Consensus-based core recommendations from the Second Stroke Recovery and Rehabilitation Roundtable.

The second Stroke Recovery and Rehabilitation Roundtable "metrics" task force developed consensus around the recognized need to add kinematic and kinetic movement quantification to its core recommendations for standardized measurements of sensorimotor recovery in stroke trials. Specifically, we focused on measurement of the quality of upper limb movement. We agreed that the recommended protocols for measurement should be conceptually rigorous, reliable, valid and responsive to change. The recommended measurement protocols include four performance assays (i.e. 2D planar reaching, finger individuation, grip strength, and precision grip at body function level) and one functional task (3D drinking task at activity level) that address body function and activity respectively. This document describes the criteria for assessment and makes recommendations about the type of technology that should be used for reliable and valid movement capture. Standardization of kinematic measurement protocols will allow pooling of participant data across sites, thereby increasing sample size aiding meta-analyses of published trials, more detailed exploration of recovery profiles, the generation of new research questions with testable hypotheses, and development of new treatment approaches focused on impairment. We urge the clinical and research community to consider adopting these recommendations.

Stability of gait and interlimb coordination in older adults.

Most falls in older adults occur when walking, specifically following a trip. This study investigated the short- and longer term responses of young (n = 24, 27.6 ± 4.5 yr) and older adults (n = 18, 69.1 ± 4.2 yr) to a trip during gait at comfortable speed and the role of interlimb coordination in recovery from tripping. Subjects walked on a self-paced treadmill when forward movement of their dominant leg was unexpectedly arrested for 250 ms. Recovery of center of mass (COM) movements and of double-support duration following perturbation was determined. In addition, the disruption and recovery of interlimb coordination of the arms and legs was evaluated. Although young and older subjects used similar lower limb strategies in response to the trip, older adults had less stable COM movement patterns before perturbation, had longer transient destabilization (>25%) after perturbation, required more gait cycles to recover double-support duration (older, 3.48 ± 0.7 cycles; young, 2.88 ± 0.4 cycles), and had larger phase shifts that persisted after perturbation (older, -83° to -90°; young, -39° to -42°). Older adults also had larger disruptions to interlimb coordination of the arms and legs. The timing of the initial disruption in coordination was correlated with the disturbance in gait stability only in young adults. In older adults, greater initial COM instability was related to greater longer term arm incoordination. These results suggest a relationship between interlimb coordination and gait stability, which may be associated with fall risk in older adults. Reduced coordination and gait stability suggest a need for stability-related functional training even in high-functioning older adults.

Head, arm and trunk coordination during reaching in children.

During postural and locomotor tasks, the orientation of the head with respect to space is maintained in order to serve as an egocentric reference value for maintaining balance. In young children during locomotor tasks, task difficulty determines the coordination of movements between head-trunk segments: the more difficult the task, the more the child limits the head on trunk movement ("en bloc") rather than letting the head move freely in space. For reaching tasks, however, there are no data about the development and maturation of coordination between the head and trunk movements and when the pattern of coordination is considered mature. The goal of this study was to characterize the development of head-trunk coordination during reaching from a sitting position in typically developing children. Forty-four typically-developing (TD) children aged from 2.8 to 11.8 years and six healthy adults participated. Children were divided into five groups (G1-G5) according to their age: 2-3, 4-5, 6-7, 8-9 and 10-11 years old. The task involved reaching towards and grasping a piece of food in the younger group or a wooden block in the older children and adults with the dominant hand, adequate to the grip size of each participant, and returning it to the mouth area to simulate self-feeding. The object was placed in line with the midline of the body at three different distances from the trunk according to the participant's arm length (two within and one beyond arm's length). Rotational movements of the head and trunk in three planes; yaw, roll and pitch, were recorded using three-dimensional tracking systems (Optotrak, Northern Digital, Model 3010 or Ariel Performance Analysis System). The variables analysed were relative head and trunk angle, absolute head and trunk angle, the anchoring index (AI) and initial direction of head and trunk rotation (direction index: DI). Patterns of head-trunk coupling were different along different axes of rotation and across groups. For the AI, a head-stabilized-on-trunk (HST) or "en bloc" pattern was observed with approximately the same frequency as a head-stabilized-in-space (HSS) pattern in the youngest children in the yaw plane for reaches within arm's length. In all other planes and for reaches of all distances, a HSS pattern was evident in the youngest children and remained consistent across the groups of children. Compared to the children, adult reaching was characterised by fixed head-trunk coordination (HST) in the roll plane at all reach distances, and greater decoupling in yaw plane motion for the two closest distances. There were no age-related differences in the pitch plane strategy which was mainly HSS. The DI patterns matured by 2-3 or 4-5 years of age, except for reaches to T1 in the pitch plane. In addition, in the roll plane, there was evidence of a two-step maturation that was not complete until adulthood. Maturation of strategies used to stabilize the head and trunk relative to each other and to the reaching arm differ across movement planes for a seated reaching task. Our data suggest that different aspects of head and trunk coordination during reaching movement mature at different rates, like for locomotor tasks previously described, and that the maturation follows a non-chronological and protracted course. These results can serve as a comparative database with which to contrast head and trunk coordination in children with movement disorders. However, in terms of typical development, these data should be considered specific for the task studied and may not reflect general principles of motor development.

Improvement of arm movement patterns and endpoint control depends on type of feedback during practice in stroke survivors.

BACKGROUND: A major challenge in stroke rehabilitation is restoration of arm motor function. Therapy-induced improvements in arm function may occur via restoration of premorbid movement patterns (recovery) or development of compensatory movement strategies. However, it is unclear whether the learning benefits of practice might be enhanced by incorporating different forms of feedback, focusing on movement outcomes or on specific arm movement patterns. OBJECTIVE: To determine if manipulation of attentional focus by providing either knowledge of results (KR) feedback, focusing on movement outcomes, or knowledge of performance (KP) feedback, focusing on arm movement patterns during repetitive practice of a pointing movement, may lead to arm motor recovery. METHODS: Twenty-eight chronic stroke survivors were randomly assigned to 2 groups that practiced 10 sessions of 75 pointing movements. During practice, groups received either 20% KR about movement precision or faded (26.6% average) KP about arm joint movements. A nondisabled control group (n = 5) practiced the same task with KR. RESULTS: Motor patterns recovered only in KP, as evidenced by immediate and long-term increases in joint range, better interjoint coordination in early movement phases, and generalization of gains. Improvements in clinical impairment and function were related to decreases in compensation (trunk rotation) and recovery of interjoint coordination in mid-movement phases. CONCLUSIONS: In stroke survivors, when the learners' attention was directed to the movements themselves (KP), motor improvements reflect recovery compared to when attention was directed toward movement outcomes (KR).

Feedback and cognition in arm motor skill reacquisition after stroke.

BACKGROUND AND PURPOSE: A debated subject in stroke rehabilitation relates to the best type of training approach for motor recovery. First, we analyzed the effects of repetitive movement practice in 2 feedback conditions (knowledge of results [KR]; knowledge of performance, [KP]) on reacquisition of reaching. Second, we evaluated the impact of cognitive impairment on motor relearning ability. METHODS: A randomized controlled clinical trial was conducted in Montreal-area rehabilitation centers between 1998 and 2003 with 37 patients with chronic hemiparesis. Patients were randomly assigned to 3 groups: (1) KR (n=14) practiced a reaching task involving 75 repetitions per day, 5 days per week for 2 weeks, with 20% KR about movement precision; (2) KP (n=14) trained on the same task and schedule as KR but with faded KP about joint motions; and (3) control (C; n=9) practiced a nonreaching task. Physical (motor impairment, function) and kinematic (movement time, precision, segmentation, variability) variables were assessed before and after (immediately, 1 month) practice. Cognitive functions (memory, attention, mental flexibility, planning) were also evaluated. RESULTS: Kinematic gains in KR (precision) and KP (time, variability) exceeded those in C and depended on memory and mental flexibility deficits. In KP, more severely impaired patients made the most clinical gains (>2xC), which were related to memory and planning abilities. CONCLUSIONS: Use of KP during repetitive movement practice resulted in better motor outcomes. Stroke severity together with cognitive impairments are important factors for choosing motor rehabilitation interventions after stroke.

Disruption of bilateral temporal coordination during arm swinging in patients with hemiparesis.

Persistent motor deficits in the paretic arm present a major barrier to the recovery of the ability to perform bimanual tasks even in individuals who have recovered well after a stroke. Impaired performance may be related to deficits in bimanual temporal coordination due to stroke-related damage of specific brain motor structures as well as changed biomechanics of the paretic arm. To determine the extent of the deficit in bilateral temporal coordination after the stroke, we investigated how bilateral reciprocal coordination was regained after external perturbations of the arm in individuals with hemiparesis due to stroke. We used a bilateral task that would be minimally affected by the unilateral arm motor deficit. Nine non-disabled control subjects and 12 individuals with chronic hemiparesis performed reciprocal (anti-phase) arm swinging in the standing position for 15 s per trial. In each trial, movement of one arm was unexpectedly and transiently (approximately 150-350 ms) arrested at the level of the wrist once in the forward and once in the backward phase of swinging. Perturbation was applied to the left and right arms in control subjects and to the paretic and non-paretic arms of individuals with hemiparesis. Kinematic data from endpoint markers on both hands and electromyographic activity of anterior and posterior deltoid muscles from both arms were recorded. The oscillatory period, the phase differences between arms and the mean EMG activity before, during and after perturbation were analyzed. In both groups the perturbation altered the period of the perturbed cycle in both the arrested and non-arrested arms and resulted in a change from anti-phase to in-phase coordination, following which anti-phase coordination was regained. Recovery of anti-phase swinging took significantly longer in patients with hemiparesis compared to control subjects. Stable pre-perturbed (anti-phase) reciprocal coordination was regained within one cycle following perturbation for the control subjects and within two cycles following perturbation for the patients with hemiparesis. Analysis of EMG activation levels showed that, compared to control subjects, there was significantly less activation of the shoulder muscles in response to perturbation in the patient group and the pattern of muscle activation in the paretic arm was opposite to that in the non-paretic and control arms. The finding that patients had a reduced capacity for maintaining and restoring the required reciprocal coordination when perturbation occurred suggests that stroke-related brain damage in our patients led to instability of bilateral temporal coordination for this rhythmical task.

Control of double-joint arm posture in adults with unilateral brain damage.

It has been suggested that multijoint movements result from the specification of a referent configuration of the body. The activity of muscles and forces required for movements emerge depending on the difference between the actual and referent body configurations. We identified the referent arm configurations specified by the nervous system to bring the arm to the target position both in healthy individuals and in those with arm motor paresis due to stroke. From an initial position of the right arm, subjects matched a force equivalent to 30% of their maximal voluntary force in that position. The external force, produced at the handle of a double-joint manipulandum by two torque motors, pulled the hand to the left (165 degrees ) or pushed it to the right (0 degrees ). For both the initial conditions, three directions of the final force (0 degrees , +20 degrees , and -20 degrees ) with respect to the direction of the initial force were used. Subjects were instructed not to intervene when the load was unexpectedly partially or completely removed. Both groups of subjects produced similar responses to unloading of the double-joint arm system. Partial removal of the load resulted in distinct final hand positions associated with unique shoulder-elbow configurations and joint torques. The net static torque at each joint before and after unloading was represented as a function of the two joint angles describing a planar surface or invariant characteristic in 3D torque/angle coordinates. For each initial condition, the referent arm configuration was identified as the combination of elbow and shoulder angles at which the net torques at the two joints were zero. These configurations were different for different initial conditions. The identification of the referent configuration was possible for all healthy participants and for most individuals with hemiparesis suggesting that they preserved the ability to adapt their central commands-the referent arm configurations-to accommodate changes in external load conditions. Despite the preservation of the basic response patterns, individuals with stroke damage had a more restricted range of hand trajectories following unloading, an increased instability around the final endpoint position, altered patterns of elbow and shoulder muscle coactivation, and differences in the dispersion of referent configurations in elbow-shoulder joint space compared to healthy individuals. Moreover, 4 out of 12 individuals with hemiparesis were unable to specify referent configurations of the arm in a consistent way. It is suggested that problems in the specification of the referent configuration may be responsible for the inability of some individuals with stroke to produce coordinated multijoint movements. The present work adds three findings to the motor control literature concerning stroke: non-significant torque/angle relationships in some subjects, narrower range of referent arm configurations, and instability about the final position. This is the first demonstration of the feasibility of the concept of the referent configuration for the double-joint muscle-reflex system and the ability of some individuals with stroke to produce task-specific adjustments of this configuration.

Deficits in adaptive upper limb control in response to trunk perturbations in Parkinson's disease.

The ability of patients with Parkinson's disease (PD) to compensate for unexpected perturbations remains relatively unexplored. To address this issue PD subjects were required to compensate at the arm for an unexpected mechanical perturbation of the trunk while performing a trunk-assisted reach. Twelve healthy and nine PD subjects (off medication) performed trunk-assisted reaching movements without vision or knowledge of results to a remembered target in the ipsilateral (T1) or contralateral (T2) workspace. On 60% of the trials trunk motion was unrestrained (free condition). On the remaining 40% of randomly selected trials trunk motion was arrested at movement onset (blocked condition). If subjects appropriately changed arm joint angles to compensate for the trunk arrest, there should be spatial and temporal invariance in the hand trajectories and in the endpoint errors across conditions. The control group successfully changed their arm configuration in a context-dependent manner which resulted in invariant hand trajectory profiles across the free and blocked conditions. More so, they initiated these changes rapidly after the trunk perturbation (group mean 70 ms). Some PD subjects were unable to maintain invariant hand paths and movement errors across conditions. Their hand velocity profiles were also more variable relative to those of the healthy subjects in the blocked-trunk trials but not in the free-trunk trials. Furthermore, the latency of compensatory changes in arm joint angles in movements toward T1 was longer in the PD group (group mean 153 ms). Finally, PD subjects' arm and trunk were desynchronized at movement onset, confirming our previous findings and consistent with PD patients' known problems in the sequential or parallel generation of different movement components. The findings that individual PD subjects were unsuccessful or delayed in producing context-dependent responses at the arm to unexpected perturbations of the trunk suggests that the basal ganglia are important nodes in the organization of adaptive behavior.

Arm-trunk coordination in the absence of proprioception.

During trunk-assisted reaching to targets placed within arm's length, the influence of trunk motion on the hand trajectory is compensated for by changes in the arm configuration. The role of proprioception in this compensation was investigated by analyzing the movements of 2 deafferented and 12 healthy subjects. Subjects reached to remembered targets (placed approximately 80 degrees ipsilateral or approximately 45 degrees contralateral to the sagittal midline) with an active forward movement of the trunk produced by hip flexion. In 40% of randomly selected trials, trunk motion was mechanically blocked. No visual feedback was provided during the experiment. The hand trajectory and velocity profiles of healthy subjects remained invariant whether or not the trunk was blocked. The invariance was achieved by changes in arm interjoint coordination that, for reaches toward the ipsilateral target, started as early as 50 ms after the perturbation. Both deafferented subjects exhibited considerable, though incomplete, compensation for the effects of the perturbation. Compensation was more successful for reaches to the ipsilateral target. Both deafferented subjects showed invariance between conditions (unobstructed or blocked trunk motion) in their hand paths to the ipsilateral target, and one did to the contralateral target. For the other deafferented subject, hand paths in the two types of trials began to deviate after about 50% into the movement, because of excessive elbow extension. In movements to the ipsilateral target, when deafferented subjects compensated successfully, the changes in arm joint angles were initiated as early as 50 ms after the trunk perturbation, similar to healthy subjects. Although the deafferented subjects showed less than ideal compensatory control, they compensated to a remarkably large extent given their complete loss of proprioception. The presence of partial compensation in the absence of vision and proprioception points to the likelihood that not only proprioception but also vestibulospinal pathways help mediate this compensation.

Arm reaching improvements with short-term practice depend on the severity of the motor deficit in stroke.

The effects of short-term, constant practice on the kinematics of a multi-joint pointing movement were studied in the hemiparetic arm of 20 chronic patients with unilateral left cerebro-vascular accident (CVA) and in 10 age- and sex-matched healthy individuals. Practice consisted of a single session of 70 pointing movements made with the right arm. Movements were made from a target located beside the body to one in the contralateral workspace, in front of the body. Vision of the final hand position was allowed after every 5th trial. At the beginning of practice, stroke patients made slower, less precise and more segmented movements, characterised by smaller active ranges of elbow and shoulder motion, disrupted elbow-shoulder coordination, as well as greater trunk movement compared with healthy subjects. With practice, healthy subjects and some patients made faster and more precise movements. These tendencies were revealed only after many repetitions (up to 55 for those with severe hemiparesis), whereas changes in healthy individuals occurred after fewer trials (approximately 20). In addition, the patients decreased movement segmentation with practice. In healthy subjects, faster movement times may be attributed to better shoulder/elbow movement timing in the first half of the reach, whereas improvement of precision was not correlated with any changes in the movement variables. In patients, improvements were accomplished differently depending on arm motor severity. For some patients with mild-to-moderate clinical symptoms, practice resulted in better timing of shoulder/elbow movements with less trunk rotation in middle to late reach. Patients with more severe impairment also improved shoulder/elbow movement timing in mid-reach but used more compensatory trunk rotation. The results suggest that even one session of repetitive practice of a multi-joint pointing task leads to improvements in movement performance-based outcome measures, but the mechanisms of improvement may vary with the individual's level of motor impairment.

Interjoint coordination dynamics during reaching in stroke.

A technique is described that characterizes the dynamics of the interjoint coordination of arm reaching movements in healthy subjects (n=10) and in patients who had sustained a left-sided cerebrovascular accident (n=18). All participants were right-handed. Data from the affected right arm of patients with stroke were compared with those from the right arm of healthy subjects. Seated subjects made 25 pointing movements in a single session. Movements were made from an initial target located ipsilaterally to the right arm beside the body, to a final target located in front of the subject in the contralateral arm workspace. Kinematic data from the finger, wrist, elbow, both shoulders and sternum were recorded in three dimensions at 200 Hz with an optical tracking system. Analysis of interjoint coordination was based on the patterns of temporal delay between rotations at two adjacent joints (shoulder and elbow). The data were reduced to a single graph (Temporal Coordination or TC index) integrating the essential temporal characteristics of joint movement (the angular displacements, velocities and timing). TC segments, duration and amplitude, were analysed. The analysis was sensitive to the differences in interjoint coordination between healthy subjects and patients with arm motor deficits. In patients, the temporal coordination between elbow and shoulder movements was disrupted from the middle to the end of the reach. More specifically, in mid-reach, all patients had difficulty coordinating elbow flexion with shoulder horizontal adduction. In addition, patients with severe arm hemiparesis had difficulty changing elbow movement direction from flexion to extension and in coordinating this change with shoulder movement. At the end of the reach, patients with severe hemiparesis had deficits in the execution of elbow extension while all patients had impaired coordination of elbow extension and shoulder horizontal adduction. In addition, active ranges of joint motions were significantly decreased in the stroke compared to the healthy subjects. Finally, TC analysis revealed significant relationships between specific aspects of disrupted interjoint coordination and the level of motor impairment, suggesting that it may be a useful tool in the identification of specific movement coordination deficits in neurological impaired populations that can be targeted in treatment for arm motor recovery.

Motor compensation and recovery for reaching in stroke patients.

OBJECTIVES: To examine the mechanisms of alternative strategies developed by stroke patients to compensate their motor impairment and their role in recovery. MATERIAL AND METHODS: The three-dimensional kinematics of the upper limb were quantified during unconstrained reaching movements in seven healthy individuals and in 15 stroke patients. Nine patients were followed-up. Individual observations were correlated with anatomical and functional brain imaging described elsewhere (Feydy et al. Stroke 2002;33:1610). RESULTS: Healthy subjects used mainly elbow extension and shoulder flexion, scaled to movement distance. Patients with hemiparesis because of stroke used different patterns of joint recruitment with different scaling rules. Patients with the greatest impairment compensated by recruiting extra degrees of freedom, particularly trunk bending. Improvement was because of a restoration towards a normal movement pattern (recovery) and/or to a reinforcement of compensation, which led to a poorer outcome. CONCLUSION: Individual behavioural data are necessary to discuss the mechanisms of functional improvement following stroke with respect to recovery and/or compensation.

Effect of trunk restraint on the recovery of reaching movements in hemiparetic patients.

BACKGROUND AND PURPOSE: Reaching movements made with the affected arm in hemiparetic patients are often accompanied by compensatory trunk or shoulder girdle movements, which extend the reach of the arm. We investigated the effects of the suppression of these compensatory movements on reaching ability in hemiparetic individuals. METHODS: Eleven healthy and 11 hemiparetic individuals participated. Three-dimensional kinematic analysis was used to quantify reaches made to a close and a distant target (near the limit of arm's length). Unrestrained reaches were compared with those in which shoulder girdle and trunk movements were restrained by a harness. RESULTS: During unrestrained reaching, abnormal trunk recruitment and limitations in elbow and shoulder movements were correlated with the degree of clinical stroke severity (r=-0.91 to -0.96) in hemiparetic patients. During trunk restraint, ranges of elbow and shoulder joint movement increased in both groups. In addition, elbow and shoulder interjoint coordination improved. This was caused by increases in the range of joint motion as well as by a better dynamic temporal relation between joints. CONCLUSIONS: Trunk restraint allowed patients with hemiparetic stroke to make use of arm joint ranges that are present but not normally recruited during unrestrained arm-reaching tasks. Thus, the underlying "normal" patterns of movement coordination may not be entirely lost after stroke. Appropriate treatments, such as trunk restraint, may be effective in uncovering latent movement patterns to maximize arm recovery in hemiparetic patients.

Hand trajectory invariance in reaching movements involving the trunk.

Movements of different body segments may be combined in different ways to achieve the same motor goal. How this is accomplished by the nervous system was investigated by having subjects make fast pointing movements with the arm in combination with a forward bending of the trunk that was unexpectedly blocked in some trials. Subjects moved their hand above the surface of a table without vision from an initial position near the midline of the chest to remembered targets placed within the reach of the arm in either the ipsi- or contralateral workspace. In experiment 1, subjects were instructed to make fast arm movements to the target without corrections whether or not the trunk was arrested. Only minor changes were found in the hand trajectory and velocity profile in response to the trunk arrest, and these changes were seen only late in the movement. In contrast, the patterns of the interjoint coordination substantially changed in response to the trunk arrest, suggesting the presence of compensatory arm-trunk coordination minimizing the deflections from the hand trajectory regardless of whether the trunk is recruited or mechanically blocked. Changes in the arm interjoint coordination in response to the trunk arrest could be detected kinematically at a minimal latency of 50 ms. This finding suggests a rapid reflex compensatory mechanism driven by vestibular and/or proprioceptive afferent signals. In experiment 2, subjects were required, as soon as they perceived the trunk arrest, to change the hand motion to the same direction as that of the trunk. Under this instruction, subjects were able to initiate corrections only after the hand approached or reached the final position. Thus, centrally mediated compensatory corrections triggered in response to the trunk arrest were likely to occur too late to maintain the observed invariant hand trajectory in experiment 1. In experiment 3, subjects produced similar pointing movements, but to a target that moved together with the trunk. In these body-oriented pointing movements, the hand trajectories from trials in which the trunk was moving or arrested were substantially different. The same trajectories represented in a relative frame of reference moving with the trunk were virtually identical. We conclude that hand trajectory invariance can be produced in an external spatial (experiment 1) or an internal trunk-centered (experiment 3) frame of reference. The invariance in the external frame of reference is accomplished by active compensatory changes in the arm joint angles nullifying the influence of the trunk motion on the hand trajectory. We suggest that to make a transition to the internal frame of reference, control systems suppress this compensation. One of the hypotheses opened to further experimental testing is that the integration of additional (trunk) degrees of freedom into movement is based on afferent (proprioceptive, vestibular) signals stemming from the trunk motion and transmitted to the arm muscles.

Stereotaxic percutaneous core biopsy versus surgical biopsy of nonpalpable breast lesions using a standard mammographic table with an add-on device.

OBJECTIVE: To determine the accuracy of using a regular mammographic table with an add-on device for biopsy of nonpalpable breast lesions in women in a community hospital setting. PATIENTS AND METHODS: During a 3-year period, 70 consenting women (39-80 years of age) with a nonpalpable mammographically suspicious lesion on routine screening mammography underwent 14-gauge automated percutaneous core biopsies, immediate needle localization and lumpectomy. The needle and surgical biopsy results were independently classified into 1 of 5 categories: cancer, fibroadenoma, fibrocystic change, normal or other. RESULTS: The procedure was well tolerated, and all core specimens yielded adequate tissue for pathologic evaluation. There were 3 episodes of vasovagal reaction. There was complete agreement in histologic findings in 64 cases (91%), including 22 of 24 cancers (92%). The overall agreement for categorizing lesions was 91% (kappa = 0.88), and there was 97% agreement (kappa = 0.94) for the classification of cancer versus benign lesion. CONCLUSION: The results are similar to those of studies performed with dedicated prone equipment. Stereotaxic core biopsies can be done safely and accurately in a community hospital setting with relatively inexpensive nondedicated mammographic equipment.

Regulation of stretch reflex threshold in elbow flexors in children with cerebral palsy: a new measure of spasticity.

The tonic stretch reflex threshold in children with cerebral palsy (CP) was measured to determine its test-retest reliability and its concurrent validity as a potential measure of spasticity. Fourteen children with spastic CP aged 6 to 18 years were tested on three separate occasions for clinical spasticity and stretch reflex thresholds of affected elbow flexors. Electromyographic (EMG) recordings were obtained by surface electrodes for elbow flexors and extensors during mechanical displacements of the passive joint towards extension. Displacements were produced by a torque motor at seven velocities which randomly varied from trial to trial. EMG activity was measured in the stretched flexor muscles to determine threshold angles and velocities for each velocity of stretch. These were plotted on a velocity-angle-phase diagram and regression analysis was used to determine the static stretch reflex threshold for each participant. The measure showed good test-retest reliability for the group (ICC 0.73, p<0.001) whereas a significant correlation between the measure and the clinical spasticity scale was not found. This technique is a potential outcome variable for measuring the efficacy of treatments aimed at decreasing spasticity in children with CP.

The timing of arm-trunk coordination is deficient and vision-dependent in Parkinson's patients during reaching movements.

The role of the basal ganglia in the coordination of different body segments and utilization of motor synergies was investigated by analyzing reaching movements to remembered three-dimensional (3D) targets in patients with Parkinson's disease (PD). Arm movements were produced alone or in combination with a forward bending of the trunk, with or without visual feedback. Movements in PD patients were more temporally segmented, as evidenced by irregular changes in tangential velocity profiles. In addition, the relative timing in the onsets and offsets of fingertip and trunk motions were substantially different in PD patients than in control subjects. While the control subjects synchronized both onsets and offsets, the PD patients had large mean intervals between the onsets and offsets of the fingertip and trunk motions. Moreover, PD patients showed substantially larger trial-to-trial variability in these intervals. The degree of synchronization in PD patients gradually increased during the movement under the influence of visual feedback. The mean and variability of the intersegmental intervals decreased as the fingertip approached the target. This improvement in timing occurred even though the separate variability in the timing of arm and trunk motions was not reduced by vision. In combined movements, even without vision, the PD patients were able to achieve normal accuracy, suggesting they were able to use the same movement synergies as normals to control the multiple degrees of freedom involved in the movements and to compensate for the added trunk movement. However, they were unable to recruit these synergies in the stereotyped manner characteristic of healthy subjects. These results suggest that the basal ganglia are involved in the temporal coordination of movement of different body segments and that related timing abnormalities may be partly compensated by vision. Abnormal intersegmental timing may be a highly sensitive indicator of a deficient ability to assemble complex movements in patients with basal-ganglia dysfunction. This abnormality may be apparent even when the overall movement goal of reaching a target is preserved and normal movement synergies appear to be largely intact.

Compensatory strategies for reaching in stroke.

A major prerequisite for successful rehabilitation therapy after stroke is the understanding of the mechanisms underlying motor deficits common to these patients. Studies have shown that in stroke patients multijoint pointing movements are characterized by decreased movement speed and increased movement variability, by increased movement segmentation and by spatial and temporal incoordination between adjacent arm joints with respect to healthy subjects. We studied how the damaged nervous system recovers or compensates for deficits in reaching, and correlated reaching deficits with the level of functional impairment. Nine right-hemiparetic subjects and nine healthy subjects participated. All subjects were right-hand dominant. Data from the affected arm of hemiparetic subjects were compared with those from the arm in healthy subjects. Seated subjects made 40 pointing movements with the right arm in a single session. Movements were made from an initial target, for which the arm was positioned alongside the trunk. Then the subject lifted the arm and pointed to the final target, located in front of the subject in the contralateral workspace. Kinematic data from the arm and trunk were recorded with a three-dimensional analysis system. Arm movements in stroke subjects were longer, more segmented, more variable and had larger movement errors. Elbow-shoulder coordination was disrupted and the range of active joint motion was decreased significantly compared with healthy subjects. Some aspects of motor performance (duration, segmentation, accuracy and coordination) were significantly correlated with the level of motor impairment. Despite the fact that stroke subjects encountered all these deficits, even subjects with the most severe motor impairment were able to transport the end-point to the target. All but one subject involved the trunk to accomplish this motor task. In others words, they recruited new degrees of freedom typically not used by healthy subjects. The use of compensatory strategies may be related to the degree of motor impairment: severely to moderately impaired subjects recruited new degrees of freedom to compensate for motor deficits while mildly impaired subjects tended to employ healthy movement patterns. We discuss the possibility that there is a critical level of recovery at which patients switch from a strategy employing new degrees of freedom to one in which motor recovery is produced by improving the management of degrees of freedom characteristic of healthy performance. Our data also suggest that stroke subjects may be able to exploit effectively the redundancy of the motor system.