Jules P. A. Dewald

Definition and Classification of Negative Motor Signs in Childhood

In this report we describe the outcome of a consensus meeting that occurred at the National Institutes of Health in Bethesda, Maryland, March 12 through 14, 2005. The meeting brought together 39 specialists from multiple clinical and research disciplines including developmental pediatrics, neurology, neurosurgery, orthopedic surgery, physical therapy, occupational therapy, physical medicine and rehabilitation, neurophysiology, muscle physiology, motor control, and biomechanics. The purpose of the meeting was to establish terminology and definitions for 4 aspects of motor disorders that occur in children: weakness, reduced selective motor control, ataxia, and deficits of praxis. The purpose of the definitions is to assist communication between clinicians, select homogeneous groups of children for clinical research trials, facilitate the development of rating scales to assess improvement or deterioration with time, and eventually to better match individual children with specific therapies. “Weakness” is defined as the inability to generate normal voluntary force in a muscle or normal voluntary torque about a joint. “Reduced selective motor control” is defined as the impaired ability to isolate the activation of muscles in a selected pattern in response to demands of a voluntary posture or movement. “Ataxia” is defined as an inability to generate a normal or expected voluntary movement trajectory that cannot be attributed to weakness or involuntary muscle activity about the affected joints. “Apraxia” is defined as an impairment in the ability to accomplish previously learned and performed complex motor actions that is not explained by ataxia, reduced selective motor control, weakness, or involuntary motor activity. “Developmental dyspraxia” is defined as a failure to have ever acquired the ability to perform age-appropriate complex motor actions that is not explained by the presence of inadequate demonstration or practice, ataxia, reduced selective motor control, weakness, or involuntary motor activity.

Pilot study to test effectiveness of video game on reaching performance in stroke

Robotic systems currently used in upper-limb rehabilitation following stroke rely on some form of visual feedback as part of the intervention program. We evaluated the effect of a video game environment (air hockey) on reaching in stroke with various levels of arm support. We used the Arm Coordination Training 3D system to provide variable arm support and to control the hockey stick. We instructed seven subjects to reach to one of three targets covering the workspace of the impaired arm during the reaching task and to reach as far as possible while playing the video game. The results from this study showed that across subjects, support levels, and targets, the reaching distances achieved with the reaching task were greater than those covered with the video game. This held even after further restricting the mapped workspace of the arm to the area most affected by the flexion synergy (effectively forcing subjects to fight the synergy to reach the hockey puck). The results from this study highlight the importance of designing video games that include specific reaching targets in the workspace compromised by the expression of the flexion synergy. Such video games would also adapt the target location online as a subjects success rate increases.

Disturbances of voluntary movement coordination in stroke: Problems of planning or execution?

Publisher Summary Thrombotic or embolic stroke in the middle cerebral artery territory of the brain in man results in a complex set of clinical signs on the contralateral side of the body including spasticity (defined primarily as an increase in muscle tone), weakness for voluntary movement, and impaired motor coordination. These three factors are not independent in their etiology because, for example, both spasticity and weakness may contribute to impaired movement coordination. However, it is now believed that incoordination is mediated primarily by a loss of appropriate control signals to limb muscles, and it is often expressed when weakness and spasticity are not severe. This chapter focuses largely on this third factor—that is, impaired motor coordination. With the exception of Levin, there has been virtually no description of limb kinematics in the impaired upper extremity of the hemiparetic subject. There are a large number of neural mechanisms that could potentially contribute to the impairment in motor coordination in human stroke syndromes. For example, based on controlled lesion studies in nonhuman primates, there is increasing information about the functional roles and connectivity of many of the cortical areas that are presumably affected by stroke lesions in man. Although the anatomical and functional features are not identical, the broad flow of information from visual areas through parietal lobes to prefrontal areas and to the motor cortex and supplementary motor areas appears to be closely comparable in human and many nonhuman primates.

Evaluation of Electroencephalography Source Localization Algorithms with Multiple Cortical Sources

Background Source localization algorithms often show multiple active cortical areas as the source of electroencephalography (EEG). Yet, there is little data quantifying the accuracy of these results. In this paper, the performance of current source density source localization algorithms for the detection of multiple cortical sources of EEG data has been characterized. Methods EEG data were generated by simulating multiple cortical sources (2–4) with the same strength or two sources with relative strength ratios of 1:1 to 4:1, and adding noise. These data were used to reconstruct the cortical sources using current source density (CSD) algorithms: sLORETA, MNLS, and LORETA using a p-norm with p equal to 1, 1.5 and 2. Precision (percentage of the reconstructed activity corresponding to simulated activity) and Recall (percentage of the simulated sources reconstructed) of each of the CSD algorithms were calculated. Results While sLORETA has the best performance when only one source is present, when two or more sources are present LORETA with p equal to 1.5 performs better. When the relative strength of one of the sources is decreased, all algorithms have more difficulty reconstructing that source. However, LORETA 1.5 continues to outperform other algorithms. If only the strongest source is of interest sLORETA is recommended, while LORETA with p equal to 1.5 is recommended if two or more of the cortical sources are of interest. These results provide guidance for choosing a CSD algorithm to locate multiple cortical sources of EEG and for interpreting the results of these algorithms.

Increased shoulder abduction loads decreases volitional finger extension in individuals with chronic stroke: Preliminary findings

The ability to open the paretic hand is greatly affected after a stroke. The loss of especially finger extension has been previously reported during isolated finger movements. However, activities of daily life require the combination of reaching and grasping which will require shoulder abduction. Shoulder abductor activity will result in concurrent elbow, wrist and finger flexion which is also referred to as the flexion synergy. Therefore as part of this study the effect of of shoulder abduction (SABD) loading on volitional finger extension in individuals with chronic stroke is investigated. We expect to observe that shoulder abduction loading will further decrease the already impaired volitional finger extension in individuals with chronic stroke. A total of four moderately impaired individuals with chronic stroke and three age-matched able-bodied subjects participated in this study. Finger extension was recorded during hand open while subjects kept their arm extended at the end of a reach. The preliminary data showed that the maximal volitional finger extension was significantly decreased by increasing the SABD loads in individuals with chronic stroke, but not in age-matched able-bodied subjects.

Aspects of Weight-Support Mechanisms in Rehabilitation Robotics

Weight support can facilitate upper-limb movements, with which the patients may do more and more meaningful exercises earlier in the rehabilitation process. Most rehabilitation devices support the arm against gravity in one way or the other. Weight support can be realized by limiting vertical displacement or applying constant supportive forces which counteract the gravitational pull. Of these, using constant supportive forces is the most natural way to facilitate natural arm movements as it allows full freedom of movement and the amount of weight support is scalable to the patients needs. To apply the supporting forces to the arm, endpoint mechanisms and exoskeletons are more complex to build and use then cable suspensions, but offer more control over the movements. Finally, passive weight support is inherently safe, but active systems have enhanced control options and the capability to create training conditions beyond limb weight.

Muscle focus: a new biomechanical-based index on the selectivity of EMG activity and its application in quantifying the muscle coactivation patterns during isometric torque generation at the elbow and shoulder

Electromyographic (EMG) recordings are widely used in the study of sensorimotor and neuromuscular systems, more specifically, in the measurement of the muscle activation patterns during isometric torque generation at the elbow and shoulder. In this paper, we introduce a new biomechanics based index of muscle focus. This new index quantifies the degree of selectivity in muscle activation during a shoulder/elbow motor task with a scalar. The muscle focus takes into account both muscle co-activation and muscle co-contraction (which is a special case of co-activation caused by activation of agonist and antagonist muscles about a single joint).

Stretch reflex gain and threshold changes as a function of elbow stretch velocity in hemiparetic stroke

The main emphasis of this study is to determine the effect of stretch velocity on stretch reflex gain and threshold during elbow extension in the paretic upper limb of 13 hemiparetic stroke subjects. Ten velocities ranging from 6 to 150/spl deg//s were applied in random fashion. The resulting reflex torques were subjected to two different quantitative approaches following subtraction of passive torques obtained at the 6/spl deg//s velocity to determine the reflex threshold and gain. Both approaches determined changes in reflex threshold and gain as a function of stretch velocity in all subjects tested. The relative effects of threshold versus gain changes on stretch reflex induced flexion torques were tested for a 60/spl deg//s increase in stretch velocity from 45/spl deg/to 105/spl deg//s. In all but one of the 13 subjects the effect of reflex gain became the predominant contributor to the reflex torque before the end of the stretch. The neurophysiological and clinical implications of these findings are discussed in the paper.

Properties of the motor unit action potential shape in proximal and distal muscles of the upper limb in healthy and post-stroke individuals

Spectral analysis of surface electromyograms (sEMG) is often used to estimate central and peripheral characteristics of a motor unit (MU) population, such as average conduction velocity, proportion of muscle fiber types, and pattern of MU recruitment. This estimation is based on the assumption that the sEMG adequately reflects the frequency characteristics of the underlying MU action potentials (MUAP). However, sEMG has limitations in this respect, based on physiological and non-physiological factors that influence its frequency content. We present a method to examine characteristics of a MU population more reliably by assessing the distributions of frequency content and amplitude for a collection of individual MUAPs, identified using high-density sEMG decomposition. We demonstrate the use of this approach to examine how MU characteristics differ across muscles and in the post-stroke state by presenting preliminary data from deltoid (DELT), biceps (BIC), and finger flexor (FF) MU populations from 12 post-stroke individuals and 8 able-bodied controls. The results show differences in the magnitude and range of MUAP median frequencies across muscles in both groups. The group median values were higher in the stroke group for the DELT and FF and lower in the stroke group for the BIC. The range of frequencies was larger in the stroke group for all muscles. The distribution of MUAP RMS amplitude in both stroke and control groups had a substantially larger range in FF than in DELT and BIC. The group median values for the FF were twice as large in the stroke group. In addition, there were differences in the frequency and amplitude results between MUAP and global sEMG analyses. The implications of these findings and possible applications of the approach are discussed.

Development of a method to quantify inter-limb coupling in individuals with hemiparetic stroke

A common motor deficit in individuals post-stroke is altered interlimb coupling. Efforts at one extremity can cause involuntary muscle activity and movement at a different extremity. An important step in understanding interlimb coupling and developing effective treatment strategies is to have an accurate quantification of the motor behavior. This paper outlines the development of an approach to measure interlimb coupling between the upper and lower extremity. Isometric and EMG based approaches were explored before determining that the use of a haptic robotic system was ideal to quantify altered interlimb coupling. This is a novel engineering approach that can measure biomechanical parameters while avoiding confounding factors. Preliminary evidence shows that lower extremity efforts cause involuntary movement in the upper extremity in stereotypical flexion and extension patterns.