Voluntary movements induce postural perturbations which are counteracted by anticipatory postural adjustments (APAs). These actions are known to build up long fixation chains toward available support points (inter-limb APAs), so as to grant whole body equilibrium. Moreover, recent studies highlighted that APAs also build-up short fixation chains, within the same limb where a distal segment is moved (intra-limb APAs), aimed at stabilizing the proximal segments. The neural structures generating intra-limb APAs still need investigations; the present study aims to compare focal movement kinematics and intra-limb APA latencies and pattern between healthy subjects and parkinsonian patients, assuming the latter as a model of basal ganglia dysfunction. Intra-limb APAs that stabilize the arm when the index-finger is briskly flexed were recorded in 13 parkinsonian patients and in 10 age-matched healthy subjects. Index-finger movement was smaller in parkinsonian patients vs. healthy subjects (p = 0.01) and more delayed with respect to the onset of the prime mover flexor digitorum superficialis (FDS, p < 0.0001). In agreement with the literature, in all healthy subjects the FDS activation was preceded by an inhibitory intra-limb APA in biceps brachii (BB) and anterior deltoid (AD), and almost simultaneous to an excitatory intra-limb APA in triceps brachii (TB). In parkinsonian patients, no significant differences were found for TB and AD intra-limb APA timings, however only four patients showed an inhibitory intra-limb APA in BB, while other four did not show any BB intra-limb APAs and five actually developed a BB excitation. The frequency of occurrence of normal sign, lacking, and inverted BB APAs was different in healthy vs. parkinsonian participants (p = 0.0016). The observed alterations in index-finger kinematics and intra-limb APA pattern in parkinsonian patients suggest that basal ganglia, in addition to shaping the focal movement, may also contribute to intra-limb APA control.
There is a body of clinical evidence to support the use of FES to improve motor control (De Kroon et al. 2002) and theoretical support from neurophysiology (Burridge & Ladouceur 2001) and motor learning research (Schmidt & Lee 1999). Iterative learning control has its origins in the control of processes that repetitively perform a task with a view to improving accuracy. The classic example is the area of trajectory following in robotics but can it be usefully applied to neurological rehabilitation?
Event Abstract Back to Event Computing with neural ensembles Miguel A. L. Nicolelis1* and Anne W. Deane1 1 Duke Center for Neuroengineering, United States In this talk, I will review a series of recent experiments demonstrating the possibility of using real-time computational models to investigate how ensembles of neurons encode motor information. These experiments have revealed that brain-machine interfaces can be used not only to study fundamental aspects of neural ensemble physiology, but they can also serve as an experimental paradigm aimed at testing the design of modern neuroprosthetic devices. I will also describe evidence indicating that continuous operation of a closed-loop brain machine interface, which utilizes a robotic arm as its main actuator, can induce significant changes in the physiological properties of neurons located in multiple motor and sensory cortical areas. This raises the hypothesis of whether the properties of a robot arm, or any other tool, can be assimilated by neuronal representations as if they were simple extensions of the subject's own body. Conference: Neuroinformatics 2008, Stockholm, Sweden, 7 Sep - 9 Sep, 2008. Presentation Type: Oral Presentation Topic: Workshop Citation: Nicolelis M and Deane AW (2008). Computing with neural ensembles. Front. Neuroinform. Conference Abstract: Neuroinformatics 2008. doi: 10.3389/conf.neuro.11.2008.01.157 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 28 Jul 2008; Published Online: 28 Jul 2008. * Correspondence: Miguel A. L. Nicolelis, Duke Center for Neuroengineering, Durham, United States, nemoABS01@frontiersin.org Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Miguel A. L. Nicolelis Anne W Deane Google Miguel A. L. Nicolelis Anne W Deane Google Scholar Miguel A. L. Nicolelis Anne W Deane PubMed Miguel A. L. Nicolelis Anne W Deane Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.
The purpose of this study was to systematically investigate how attentional and motor demands influence motor overflow production in both young adults and healthy older adults. Motor overflow is involuntary muscle activity that may coincide with voluntary movement and is thought to increase with old age. Seventeen young adults, aged 18-35, and 17 older adults, aged 60-80 years, performed a finger pressing task and exerted a percentage of their maximal force output with one hand while overflow was recorded in the passive hand. Required target force output was either 33% or 66% of maximal force and for half the trials was performed with the participants? non-dominant hand. Attention was manipulated by presenting a tactile stimulus to one or both hands for certain trials. Results indicated that older adults exhibited greater overflow compared to their younger counterparts. Although both age groups displayed greater overflow at the lower target force, this effect was exacerbated in older adults. Furthermore, overflow in older adults, but not young adults, was greater when attention was directed to one or both hands during task performance. No significant intermanual asymmetry in overflow production was found for either age group. Importantly, task performance measures suggested that both age groups were able to effectively perform the task, although older adults were significantly more variable. When attention and motor demands were imposed there was greater variability in both task performance and level of overflow production. Collectively, the increase in motor overflow in old age has been interpreted as evidence of possible bilateral cortical activation which may be influenced by increased task demands. In order to compensate for age-related brain deterioration and perform comparatively to younger adults, older adults may recruit an increased cortical network of brain regions to meet task demands.
Previous research has demonstrated that intra- and inter-personal rhythmic interlimb coordination are both constrained by the self-organizing entrainment process of a coupled oscillator dynamic. In particular, both intra- and inter-personal coordination exhibit the same stable macroscopic movement patterns (i.e., inphase and antiphase). The variability of inter-personal coordination, however, is typically found to be much greater than the variability observed for intra-personal coordination. Researchers have assumed that this is due to a difference in the strength of the attractor dynamic that underlies these two forms of rhythmic interlimb coordination. More specifically, the visual-motor coupling of inter-personal coordination is assumed to result in a weaker attractor dynamic than the neuro-muscular coupling of intra-personal coordination. Two experiments were conducted to evaluate this conjecture. Pairs of participants swung hand-held pendulums about the wrist either inphase or antiphase, both intra- and inter-personally. The cross-recurrence statistics of %REC and Maxline were used to independently index the level of noise and the attractor strength of the coordination, respectively. The attractor strength for inter-personal coordination was significantly weaker than the attractor strength for intra-personal coordination. However, the magnitude of noise underlying the two types of coordination was similar. Discussion will focus on (1) the ability of cross-recurrence analysis to independently index the noise and attractor strength of rhythmic interlimb coordination, and (2) possible reasons for a weaker attractor in visual-motor coupling than in neuro-muscular coupling.
Introduction. Performing some motor tasks, especially in high-performance sports, requires perfect interaction between the sensory and motor systems. The conviction that experts in acrobatics, gymnastics or dancing should have a great sense of balance is very common. The object of this research project was (1) to establish the effect of expertise in acrobatics on postural control and (2) to determine how stable is the strategy of movement control during performing a balancing on a movable platform in different conditions. Methods. The research experiment was conducted on 11 high-level acrobats aged 21,3?1,7 and 22 students aged 21,1?1,1 (control group). The subjects were examined using a stabilometer. The subjects were maintaining balance while standing on a movable platform of a stabilometer. The task was to keep balance standing on the stabilometer for 30sec while movements of platform were affected by person?s behavior. Two parameters were calculated to characterize the dynamic balancing performance: instability (integral of average module of inclination) (degree/s), which were interpreted as a total error and balancing control (number of corrections), which describes a strategy of balancing. Balancing tasks were performed in A/P and M/L plane. All tests were carried out with and without visual control in both planes on the ground level and on the 50 cm high platform. Results. The achieved empirical data and its analysis allowed to conclude that acrobats have significantly better balance control then students. Nevertheless very few differences were not statistically significant. Examined experts were better then students performing tasks 50 cm above the ground level (p<0,001) and tasks with lack of vision (p<0,01). Interestingly, the total amount of corrections was almost the same in all measurements in acrobats. It was observed that amount of corrections increased in more difficult conditions in control group. Values of average inclination and number of corrections were significantly correlated in students (p<0,05). Conclusion. Practicing acrobatics contributes to the development of specific postural control strategies, which is relatively stable in different conditions while balancing on a movable platform.
In a recent study it was shown that the ability to use motor imagery was compromised in right congenital hemiparesis, viz. left hemisphere damage (Mutsaarts et al., 2006). However, posture of the displayed stimuli and the actual posture of the hand making the response were incongruent in that study. Ample evidence exists that such an incongruency negatively influences laterality judgements in a motor imagery task, which may have affected the findings in the Mutsaarts et al. (2006) study. In the present study, three participant groups (controls participants, participants with left hemiparesis, and participants with right hemiparesis [all n=11]) were engaged in a motor imagery task in which the posture of the displayed drawings of the hands and the posture of the hand of the participant making the response were congruent. It was hypothesised that this postural congruency would facilitate motor imagery in participants with right hemiparesis. Participants had to make laterality judgments as quickly as possible upon appearance of the rotated stimuli (i.e., hands) on a screen. The results showed significant linear effects of rotation angle on reaction times for all three groups. In addition, the number of errors made was far below chance level. These findings suggests that motor imagery in right hemiparesis is still intact, but is critically dependent on the congruency between posture of the stimulus and posture of the hand making the response. Furthermore, the influence of hand posture on motor imagery shows that motor imagery is an embodied cognitive process. Reference Mutsaarts, M., Steenbergen, B., & Bekkering, H. (2006). Impaired motor imagery in right hemiparetic cerebral palsy. Neuropsychologia, 45(4), 853-9.
Abstract Cerebral palsy belongs to a group of cerebral disorders due to an injury in the immature brain during the first years of life, causing motor alterations responsible for compromising the performance of functional activities. The instruments used to evaluate the motor function in children with cerebral paralysis were: GMFM, PEDI, Melbourne Assessment, Jebsen-Taylor and GMFCS, were applied with the purpose to optimize the definition of the intervention objectives, compare the effectiveness of treatment and to facilitate communication of the interdisciplinary team. Objective: The purpose of this study was to verify, through literature revision, the effectiveness of the evaluation scales of motor function in children with cerebral palsy and to analyze its properties critically. Methods: The research and choice of articles were carried out utilizing databases of the Medline, Lilacs, PubMed, Cochrane and Scielo, from 1969 to 2006, through the describers of cerebral palsy and motor activity. The enclosed studies have been related to the instruments of evaluation of motor function in children with cerebral palsy and the ones that compared its psychometric properties. The ones that used instruments for some specific intervention were excluded. Results: We found 72 articles, and 13 had been enclosed in the revision. The studies relate on psychometric properties of the instruments and compare the scales between themselves. Most of them, seven (7) are on the GMFM, followed by PEDI and GMFCS while few authors mention the Melbourne Assessment and Jebsen-Taylor. Discussion: The GMFM is a method used world-wide, and there are many studies that confirm its properties. The PEDI is reliable validation and it is the only one adapted to Brazilian culture that evaluates the motor function of different forms of the GMFM. Both are distinct methods that applied together complement themselves resulting in a wide range evaluation and a possible prognosis if associated to the GMFCS. The other methods consist in a reduced number of studies, however, sufficient enough to define the psychometric properties and its use in clinical practice. Conclusion: All the instruments are effective in investigating the motor function in children with cerebral palsy. The GMFM and PEDI are instruments used in world-wide literature, however only one method cannot serve all the groups, leaving the physical therapist responsible for choosing which method is more indicated for the objectives of his patient.
When manipulating objects, we must control our hand motion as well as the interaction forces that arise from contact with the environment. At the level of musculoskeletal biomechanics, motions and forces are coupled by intrinsic limb impedance. However, it has yet to be established whether at the neural level the control of motion and force are coupled or independent. Here we provide evidence for the existence of independent neural controllers for arm motion and interaction forces. This evidence is offered by transcranial magnetic stimulation (TMS) of posterior parietal cortex (PPC) resulting in the differential disruption of the control of motion but not of force. We designed three experimental conditions where force and position control tasks appeared in combination or separately. Accordingly, our experiment consisted of three blocks: Combined, Force, and Motion. During the Combined block subjects applied force to the handle of the manipulandum in a leftward direction as it was moved to center out positions along a smooth trajectory. This block required the simultaneous control of motion and force. During the Force block subjects maintained an applied force as the manipulandum moved along a very slow constant velocity profile in which inertial effects were negligible. In this condition, the quality of force control was assessed by quantifying the ability of the subjects to maintain constant force vectors at different arm configurations. In the Motion block subjects were asked to track a predetermined movement trajectory. In order to compare performance in this and in the other tasks, subjects were required to track a predictable motion of the manipulandum while maintaining contact with it. A perfect position controller would produce perfect tracking, thus resulting in zero interaction force between the subject and the manipulandum. Deviation from zero force was attributed to errors in the ability of the subject to track the desired trajectory. Single pulse TMS was applied to left PPC during all blocks after learning. We found (a) that TMS stimulation results in disruption of performance during the Combined and Motion blocks, but not the Force Block. Furthermore, (b) at the end of learning, a simple summation of forces from the Motion block and the Force block describe 80-97% of the variability of forces applied in the Combined block. These results are consistent with the presence, after learning, of independent force and motion controllers. They also suggest that PPC is critical to the neural control of hand motion but not of interaction force.
The performance of elite athletes is strongly dependent of a good motor control and muscular coordination, mainly when precision is required. Due to this, coaching paralympic athletes with neurological sequelae such as those of Poliomyelitis is a challenging task, since training methodology must be fitted to each athlete. In this sense, it is important to evaluate relevant aspects of motor abilities of these athletes. This was done in the case of a female paralympic athlete, with sequelae of polio, integrating the athletics team of CEDE-PUCPR, specialist in throwing events. Despite of good results in competitions, her throwing pattern is not regular. During her shoulder isokinetic evaluation, the torque curve showed anomalous behavior and by arm cranking she was not able to maintain a regular rhythm. It was conjectured that irregular muscular activation patterns are related of this behavior. In order to investigate it, the electromyographic activity of the biceps and triceps brachii was registered during arm cranking. Electromyography bipolar electrodes were positioned over the biceps and triceps brachii and the signal was collected with the equipment EMG1600CA (EMGSystem) with a sampling rate of 1 kHz and filtering between 20 Hz and 500 Hz. The athlete was firmly attached to the chair of a mechanical ergometer M4100 (Cefise) and then asked to perform three series of four minutes each, with interval of 10 minutes between them. During each series, the cadency was progressively increased, from 40 RPM until 70 RPM, increasing 10 RPM in each minute. The electromyographyc activity has shown the presence of co-contractions in both arms, but they appeared more frequently on the left side (non-dominant). When left pushing and right pulling, the left biceps have shown amplitude 5 times higher than that of the right biceps. The behavior has changed over the series: during the first series, the activation of muscles of the left sides was higher if compared to their right counterparts; during the second series there was a more symmetric behavior. During the third series, besides the interlimb asymmetry, it was observed that the left biceps remained activated along all the series. The results of this preliminary analysis have shown that muscular activation patterns might be the reason for the irregular throwing behavior. However, a more detailed analysis of the electromyographyc signals is necessary to identify the mechanisms behind it and help designing a training program to correct the activation patterns and improve the throwing performance.
Background: The flexion relaxation phenomenon (FRP) is an interesting model to study the modulation of lumbar stability. Previous investigations have explored the effect of load, angular velocity and posture on this particular response. However, the influence of muscular fatigue on FRP parameters has not been thoroughly examined. The objective of the study is to identify the effect of erector spinae (ES) muscle fatigue and spine loading on myoelectric silence onset and cessation in healthy individuals during a flexion-extension task.Methods: Twenty healthy subjects participated in this study and performed blocks of 3 complete trunk flexions under 4 different experimental conditions: no fatigue/no load (1), no fatigue/load (2), fatigue/no load(3), and fatigue/load (4). Fatigue was induced according to the Sorenson protocol, and electromyographic (EMG) power spectral analysis confirmed that muscular fatigue was adequate in each subject. Trunk and pelvis angles and surface EMG of the ES L2 and L5 were recorded during a flexion-extension task. Trunk flexion angle corresponding to the onset and cessation of myoelectric silence was then compared across the different experimental conditions using 2 x 2 repeated-measures ANOVA.Results: Onset of myoelectric silence during the flexion motion appeared earlier after the fatigue task. Additionally, the cessation of myoelectric silence was observed later during the extension after the fatigue task. Statistical analysis also yielded a main effect of load, indicating a persistence of ES myoelectric activity in flexion during the load condition.Conclusion: The results of this study suggest that the presence of fatigue of the ES muscles modifies the FRP. Superficial back muscle fatigue seems to induce a shift in load-sharing towards passive stabilizing structures. The loss of muscle contribution together with or without laxity in the viscoelastic tissues may have a substantial impact on post fatigue stability.
Although the motor system is primarily crossed with each hemisphere controlling movement primarily on the contralateral side, more subtle ipsilateral control is also present. Importantly, different aspects of movement are controlled by each hemisphere, and our results, based on studying ipsilesional reaching in stroke patients with unilateral damage, show that damage to the left hemisphere produces deficits in the movement trajectory and damage to the right hemisphere produces deficits in final position. These findings are consistent with hand preference effects in healthy right handers and with the conclusion that the left hemisphere is more important for feedforward dynamic control and the right hemisphere is more important for online control.
Prolonged standing has been associated with the onset of low back pain symptoms in working populations. So far, it is unknown how individuals with chronic low back pain (CLBP) behave during prolonged unconstrained standing (PS). The aim of the present study was to analyze the control of posture by subjects with CLBP during PS in comparison to matched healthy adults. The center of pressure (COP) position of 12 CLBP subjects and 12 matched healthy controls was recorded in prolonged standing (30min) and quiet stance tasks (60s) on a force plate. The number and amplitude of COP patterns, the root mean square (RMS), speed, and frequency of COP sway were analyzed. Statistical analyses showed that CLBP subjects produced less postural changes in the antero-posterior direction with decreased postural sway during the prolonged standing task in comparison to the healthy group. Only CLBP subjects were influenced by the prolonged standing task, as demonstrated by their increased COP RMS, COP speed and COP frequency in the quiet standing trial after the prolonged standing task in comparison to the pre-PS trial. The present study provides additional evidence that individuals with CLBP might have altered sensory-motor function. Their inability to generate responses similar to those of healthy subjects during prolonged standing may contribute to CLBP persistence or an increase risk of recurrent back pain episodes. Moreover, quantification of postural changes during prolonged standing could be useful to identify CLBP subjects prone to postural control deficits.
Stroke is the leading cause of permanent impairment and disability. MIT-MANUS, a robotic device which interactively treats stroke survivors, has been delivering targeted training for the paretic shoulder and elbow. In randomized controlled trials involving over 300 persons with both acute and chronic impairments after stroke, persons treated with the robotic protocol have demonstrated significant reductions in impairment in the exercised limb. We have expanded the trials for other limb segments including the wrist, the hand, and the ankle. I will discuss past and on-going trials, including a set of clinical trials with over 100 stroke patients in which the robot had distinct behaviors (progressive strength training, sensorimotor training, and performance-based training). While the robot possesses the native ability to record kinematic and force data, an ongoing challenge is to extract meaningful data from these measurements. Using the set of trials described above (different forms of robot training), I will show that robot-based assessment affords a unique insight into the relative advantage and disadvantage of each of these forms of training and this insight might support the clinician in selecting different protocols based on patient specific deficit. I will then discuss whether stroke patients are able to generalize recovery on the same and distinct workspace, as well as across distinct joints, and whether this generalization occurs in joint- or world-space. These results have important practical consideration as it is common clinical practice to advocate that training must be task-specific. I will conclude by exploring different definitions of synergies among the clinical and neuroscience communities and show results from 164 stroke patients, both inpatient and outpatient that might help in clarifying these distinct definitions and their impact on neuro-recovery.
INTRODUCTION: Cervical dystonia (CD) is the most common type of focal dystonia. It is characterized by involuntary contractions of neck muscles, which results in abnormal movements and postures of head and neck. Physical therapy may have beneficial effects on CD because the ?forced? posture associated to abnormal motor performance may provoke limitations in cervical range of motion (CROM) and muscle weakness in neck, shoulder and trunk. Until now, hardly any study has focused on the role of physical therapy effects on CD. OBJECTIVE: To investigate the effects of a physical therapy program consisting of muscle strengthening and CROM exercises in a patient with CD. METHODS: This was a single subject design study with a 48-year-old CD patient. She had right laterocollis, right torticollis, elevation of the right shoulder and left scoliosis. Physical therapy program consisted of exercises to improve CROM, as well as strengthening and stretching exercises for neck, shoulder and trunk muscles. The patient attended to fifty sessions three times a week. Assessments were accomplished in four different periods: baseline (before intervention); intervention; immediately after intervention; and follow-up (eight weeks after intervention). In each period, the patient was evaluated in three different days with a seven-day interval between measures. Mean outcome measures were: CROM measures with Cervical Range-of-Motion Device and isometric muscle torque with Nicholas Manual Muscle Tester hand-held dynamometer. Visual analysis of data was selected for statistical analysis. RESULTS: This study includes only the results for CROM and neck muscles? torque. There was a tendency of improvement for CROM of extension and rotation to the right, with maintenance of these values on follow-up. CROM of flexion, left and right lateral flexion and left rotation tended to improve during and after intervention. CROM of retraction showed a clear trend of improvement along the study, returning, however, to basal values on follow-up. Neck?s muscle torque also tended to improve throughout and after intervention for of all tested muscles. However, throughout follow-up, neck extensors, right and left lateral flexors and left rotators tended to maintain gains obtained at the end of intervention, whereas flexors and right rotators returned to basal values. CONCLUSIONS: The applied intervention tended to cause benefits on CROM and muscle torque, especially in movements to the left. Findings of the present study suggest that the elected physical therapy program may be a promising method for treatment of CD and, therefore, it should be further investigated.
It is well accepted that physiological and mechanical properties of skeletal muscle alter with daily preferential use. Traditionally, motor unit properties have been investigated by means of the electromyographic (EMG) signal, with the aim of elucidating which strategies could be better associated with handedness. This study intended to compare dominant and non-dominant arms based on the mechanomyographic (MMG) signal. The rational of using the MMG signal as an alternative method to investigate the muscle activity is supported by the fact that each motor unit action potential (MUAP), when reaches its muscle fibers, produces some mechanical oscillations related with the developed tension (usually defined as muscle twitch). A muscle twitch represents dimensional changes that occur either on the transverse or longitudinal axis. Thirty-nine healthy volunteers, divided in two groups: nineteen males (mean age 25,3 ? 8,1 years), and twenty females (mean age 20,6 ? 2,6 years) performed unfatigued isometric contractions at five different intensities (including 100% of maximal voluntary contraction (MVC): 20%, 40%, 60%, and 80% of MVC) while MMG signals were collected from dominant and non-dominant biceps brachii muscles through an accelerometer. During the tests the subject had visual feedback through a target line shown in the video screen, related to the degree of force that he had to keep and was instructed to track the force target line with a minimum of overshooting. The mean frequency (MF) and the RMS value were calculated from the MMG signals coming from lateral oscillations of muscle fibers. RMS values increased with the contraction level, but with differences between genders. MF values decreased with the increase of muscle contraction. Both parameters were not consistent on pointing out any difference between the dominant and non-dominant arms. The results suggest that the summation of muscle twitches, measured by means of two features computed from MMG signals collected using accelerometers, seem not to reveal any difference of biceps brachii muscle between dominant and non-dominant arm during isometric contractions. To our knowledge, this is the first study that compares the MMG signal between both arms. It is well known that within the same muscle the motor unit recruitment and frequency pattern strategies vary depending on the motor task requested and whether the muscle is acting as agonist or antagonist. Thus, we suggest that different muscles performing similar tasks must be also considered for analysis through the MMG signal.
Introduction Previous research has demonstrated that adults can adapt to novel sensorimotor perturbations, a process thought to be achieved by the gradual update of an internal representation (e.g., Shadmehr & Mussa-Ivaldi, 1994). However, few research studies have investigated the persistence of a newly acquired representation, as assessed by the reduction of performance errors after the perturbation has been removed (i.e., de-adaptation). The current study employed two distinct visuomotor distortions (feedback rotation or gain) that created movement errors in the radial or azimuthal directions, respectively. It has been previously demonstrated that the central nervous system (CNS) relies more heavily on visual input for hand localization in the azimuthal direction, whereas proprioception is more heavily weighted in the radial direction (van Beers et al., 1999). The objective of this research was to determine if visual and proprioceptive afference could be flexibly re-weighted in order to de-adapt to novel sensorimotor perturbations. Method Seventy-two right-handed adults performed a center-out reaching task on a digitizing tablet positioned below a horizontally-oriented computer monitor that provided visual feedback of target circles and task performance. During adaptation trials, participants were exposed to either an incremental visuomotor rotation or a gain distortion. During the subsequent post-exposure phase, the visual feedback was provided in one of three ways: 1) on-line visual feedback with knowledge of end-point position, or 2) no on-line feedback but visual end-point position, or 3) neither on-line feedback nor end-point position. Performance was assessed by standardized initial directional error (IDE) and initial amplitude error (IAE) for the rotation and gain distortion tasks, respectively. Results All participants demonstrated strong aftereffects in the post-exposure phase, indicative of adaptation to the visuomotor perturbations. To assess between-group differences in rate and final level of de-adaptation, distortion by feedback (2 x 3) ANOVAs were conducted. Results indicate that the participants primarily utilized visual afference to de-adapt to both distortions, despite the fact that adaptation to the visual rotation resulted in movement errors in azimuth, whereas gain adaptation resulted in movement extent errors. Conclusions Consistent with Jones et al. (2001), proprioceptive input is down-weighted during exposure to a visuomotor distortion in order to resolve the experimentally-introduced visuo-proprioceptive conflict. Proprioception continues to be down-weighted during the post-exposure phase despite the removal of the sensory conflict, suggesting the CNS fails to flexibly re-weight sensory information during visuomotor de-adaptation. These data will be discussed with preliminary findings investigating multisensory integration during a reaching task that manipulates proprioceptive, as opposed to visual, information. Supported by: NIH R01HD42527and NIH RO3HD050372
The randomized clinical study of neurorehabilitation of walking included acute hemiplegic individuals who could stand, but could walk only assisted by a therapist or a walker. Subjects participated in a 4-week program that comprised 30 minutes long daily walking sessions augmented with multichannel electrical stimulation that was timed to promote the stance (to channels) and the swing (3 channels) of the paretic leg. The main outcome measures were the walking speed and symmetry index. Significant improvement in the walking speed and symmetry index, compared to the control group, was found at the end of therapy. Significant difference was also found when comparing the end of the therapy with the beginning in both groups. In the follow up study (6 months) the differences were decreased; yet, they were still statistically significant between the groups. The finding was that the patterned electrical stimulation must better fit into the preferred walking pattern of the hemiplegic individual. The intragroup differences must be considered and sensory driven control should be applied for the best result. The results indicate that intensive exercise augmented with patterned electrical stimulation contributes to the faster recovery of function. This suggestion is now being confirmed by fMRI and TMS studies. The case studies in chronic subjects indicate that the period of dose used in the study with acute hemiplegic should be increased for better outcome.
