Analysis of motor characteristics of reaching movements in children with cerebral palsy.

Studies confirm that children with cerebral palsy (CwCP) have difficulty with simple, everyday movements like reaching for objects. Accurate reaching requires that shoulder and elbow joints are coordinated to move the hand along a smooth path to the desired target location. Here we examined multijoint coordination by comparing reaching performance in the affected and unaffected limbs of CwCP (nine children, six girls and three boys, aged 8-10 years) to reaching performance in the non-dominant and dominant limbs of typically-developing age- and gender-matched control (CTR) children. The hypothesis was that CwCP would show the effects of coordination deficits in both their affected and unaffected limbs. All children performed two sessions (one session with each arm) of speeded reaching movements to three targets arranged to manipulate the required pattern of shoulder and elbow coordination. The movements were tracked with a motion tracker allowing us to assess the following measures: movement distance, duration, and speed, hand-path deviation from linearity, final position accuracy and precision, and measures of shoulder and elbow excursion. We found that CwCP made reaches that covered a greater distance and took more time, that their shoulder and elbow rotations were larger, and that their movements showed greater deviation from linearity than the movements performed by CTR children. Children with CP were also more variable than CTR children on every measure except movement duration. The pattern of shoulder and elbow rotation observed in the CwCP group represents a coordination pattern that is significantly different from the pattern used by CTR children and may represent a greater reliance by CwCP on proximal muscular control systems. The discussion section considers the role that the cortical-spinal system may play in multijoint coordination.

Spiking Neural Networks Diagnosis of ADHD subtypes through EEG Signals Evaluation.

Attention-deficit hyperactivity disorder (ADHD) affects at least 5% of the world population and can disturb normal development causing serious issues in adulthood. Therefore, it is important to develop tools to help detecting ADHD so that treatment can start as soon as possible. Plus, the differentiation of ADHD in its subtypes is important to define the recommended treatment. Here we present original research to investigate the hypothesis of using a Spiking Neural Networks (SNN) EEG signals classifier for automated diagnostic of ADHD subtypes. This research used data from 243 patients and healthy volunteers acquired as part of the Healthy Brain Network. These resting state EEG signals were collected from 5-minutes scan with a 128 channel 500 Hz system. For benchmarking, we present a comparison of the SNN performance with a support vector machine, a k-nearest neighborhood, a random forest algorithm and a multi-layer perceptron. We present experiments for both the diagnostics of ADHD and for detecting which ADHD subtype the patient has. SNN presented a 72.00% accuracy for detecting ADHD surpassing all the other techniques by 9.1 % and 68% in detecting if the subject is a member of the Combined ADHD, Inattentive ADHD or control groups (18% better than the second-best technique). Clinical Relevance - This work has shown a resource that can be useful allied to other tools to help diagnosing ADHD and its subtypes.

Developing an Upper Limb Kinematics Database of Activities of Daily Living.

Open-access databases can facilitate data sharing among researchers and provide normative data for objective clinical assessment development, robotic design, and biomechanical modeling. However, most existing databases focus on gait, balance, and hand gestures without providing elbow and shoulder kinematics that are required in activities of daily living. Furthermore, the few existing upper limb datasets include small sample sizes without consistent data collection protocols, which hinder robotic engineers' ability to design robotic devices that accommodate the general population. To address the literature gap, an open-access upper limb kinematic database was proposed. Due to the impact of COVID-19 on human research, only data from 16 participants were collected. Clinical Relevance-This provides baseline kinematics for developing objective clinical assessments and rehabilitation robots.

Actor-Critic Reinforcement Learning Based Algorithm for Contaminant Minimization in sEMG Movement Recognition.

This paper aims to present an approach based on Reinforcement Learning (RL) concept to detect contaminants' type and minimize their effect on surface electromyography signal (sEMG) based movement recognition. The referred method was applied in the pre-processing stage of a sEMG based motion classification system using the Ninapro database 2 artificially contaminated with electrocardiography (ECG) interference, motion artifact (MOA), powerline interference (PLI) and additive white Gaussian noise (WGN). Support Vector Machine was the method for movement classification. The results showed an improvement of 8.9%, 16.7%, 15.9%, 16.5%, and 11.9% in the movement recognition accuracy with the application of the pre-processing algorithm to restore, respectively, one, three, six, nine, and 12 contaminated channels.

Actor-Critic Reinforcement Learning Based Algorithm for Contaminant Type Identification in Surface Electromyography Data.

This paper aims to present an innovative approach based on Reinforcement Learning (RL) concept to detect contaminants' type and minimize their effect on surface electromyography signal (sEMG). An agent-environment model was created based on the following elements: environment (muscle electrical activity), state (set of six features extracted from the signal), actions (application of filters/procedures to reduce the impact of each interference), and agent (controller, which will identify the type of contamination and take the appropriate action). The learning was conducted with Actor-Critic method. An average accuracy of 92.96% was achieved in an off-line experiment when detecting four contaminant types (electrocardiography (ECG) interference, movement artifact, power line interference, and additive white Gaussian noise).

Interlimb differences in visuomotor and dynamic adaptation during targeted reaching in children.

While a number of studies have focused on movement (a)symmetries between the arms in adults, less is known about movement asymmetries in typically developing children. The goal of this study was to examine interlimb differences in children when adapting to novel visuomotor and dynamic conditions while performing a center-out reaching task. We tested 13 right-handed children aged 9-11 years old. Prior to movement, one of eight targets arranged radially around the start position was randomly displayed. Movements were made either with the right (dominant) arm or the left (nondominant) arm. The children participated in two experiments separated by at least one week. In one experiment, subjects were exposed to a rotated visual display (30° about the start circle); and in the other, a 1 kg mass (attached eccentrically to the forearm axis). Each experiment consisted of three blocks: pre-exposure, exposure and post-exposure. Three measures of task performance were calculated from hand trajectory data: hand-path deviation from the straight target line, direction error at peak velocity and final position error. Results showed that during visuomotor adaptation, no interlimb differences were observed for any of the three measures. During dynamic adaptation, however, a significant difference between the arms was observed at the first cycle during dynamic adaptation. With regard to the aftereffects observed during the post-exposure block, direction error data indicate considerably large aftereffects for both arms during visuomotor adaptation; and there was a significant difference between the arms, resulting in substantially larger aftereffects for the right arm. Similarly, dynamic adaptation results also showed a significant difference between the arms; and post hoc analyses indicated that aftereffects were present only for the right arm. Collectively, these findings indicate that the dominant arm advantage for developing an internal model associated with a novel visuomotor or dynamic transform, as previously shown in young adults, may already be apparent at 9 to 11-year old children.

Movement Kinematics and Interjoint Coordination Are Influenced by Target Location and Arm in 6-Year-Old Children.

Rapid aiming movements are typically used to study upper limb motor control and development. Despite the large corpus of work in this area, few studies have examined kinematic manual asymmetries in children who have just started formal schooling and until now, none have characterized how children coordinate their joints to complete these movements (i.e., interjoint coordination). In the present study, manual asymmetries in kinematics and interjoint coordination in strongly right-handed 6-year-old children were investigated when reaching for ipsilateral and contralateral targets with their dominant right arm and the non-dominant left arm. Overall, manual asymmetries in interjoint coordination are apparent for both 6-year-old children and young adults, although young children completed the task by adopting a different strategy than adults. Also, control strategies employed by 6-year-old children were influenced by both the location of the target as well as the arm used to perform the task. Specifically, compared to all other conditions, children's trajectories were more curved when performing contralateral movements with the non-dominant left arm, which were driven by smaller shoulder excursions combined with larger elbow excursions for this condition. Based on these results, we argue that the differences in interjoint coordination reflect the stage of development of 6-year-old children, the origin of which derives from maturational (e.g., hand dominance) and environmental factors (e.g., school-based experience).

Genetic Algorithm Application to Feature Selection in sEMG Movement Recognition with Regularized Extreme Learning Machine.

This paper presents a genetic algorithm (GA) feature selection strategy for sEMG hand-arm movement prediction. The proposed approach evaluates the best feature set for each channel independently. Regularized Extreme Learning Machine was used for the classification stage. The proposed procedure was tested and analyzed applying Ninapro database 2, exercise B. Eleven time domain and two frequency domain metrics were considered in the feature population, totalizing 156 combined feature/channel. As compared to previous studies, our results are promising - 87.7% accuracy was achieved with an average of 43 combined feature/channel selection.

Recurrent Neural Network for Contaminant Type Detector in Surface Electromyography Signals.

A surface Electromyography (sEMG) contaminant type detector has been developed by using a Recurrent Neural Network (RNN) with Long Short-Term (LSMT) units in its hidden layer. This setup may reduce the contamination detection processing time since there is no need for feature extraction so that the classification occurs directly from the sEMG signal. The publicly available NINAPro (Non-Invasive Adaptive Prosthetics) database sEMG signals was used to train and test the network. Signals were contaminated with White Gaussian Noise, Movement Artifact, ECG and Power Line Interference. Two out of the 40 healthy subjects' data were considered to train the network and the other 38 to test it. Twelve models were trained under a -20dB contamination, one for each channel. ANOVA results showed that the training channel could affect the classification accuracy if SNR = -20dB and 0dB. An overall accuracy of 97.72% has been achieved by one of the models.

Gait characteristics of younger-old and older-old adults walking overground and on a compliant surface / Características da marcha de idosas jovens e muito idosas em solo estável e sobre superfície complacente

BACKGROUND: Walking across unstable surfaces disturbs normal stability and efficient strategies must be used to avoid falls. This study identified age-related changes in gait during unstable surface walking. METHOD: Eight healthy younger-old adults (YOG, mean age, 68.6 years) and eight healthy older-old adults (OOG, mean age, 82.1 years) were assessed. Both groups performed the Timed Up and Go Test (TUG) and walked on a rigid and on a compliant surface while kinematic data were obtained. RESULTS: The OOG needed more time to complete the TUG test compared to YOG (F1,14=5.18; p=0.04). The gait speed, stride length and vertical displacement of the foot were similar for both groups, but they were slower (F1,14=5.64; p=0.03) when walking on the compliant surface. The knee and hip range of motion on the sagittal plane (F1,14=191.9; p<0.001 and F1,14=36.4, p<0,001, respectively) increased on the complaint surface but no group effect was found. The displacement of upper trunk on the frontal plane was similar between groups (F1,14=2.43; p=0.14) and conditions (F1,14=1.15; p=0.3). The OOG had greater displacement of the pelvic segment on the frontal plane than the YOG (F1,14=4.9; p=0.04) mainly for the complaint surface. CONCLUSIONS: Older-old individuals have slower TUG test and greater displacement of the pelvic segment on a compliant surface. More challenging tasks and/or environment should be used for gait assessment and intervention of older adults with risk of falls.

CONTEXTUALIZAÇÃO: Caminhar em superfícies instáveis perturba a estabilidade corporal, e estratégias eficientes devem ser utilizadas para evitar quedas. Objetivo: Identificar alterações da marcha relacionadas ao envelhecimento durante a caminhada em superfície instável. MÉTODO: Oito idosos jovens sadios (GIJ, idade média, 68,6 anos) e oito idosos muito idosos sadios (GMI, idade média, 82,1 anos) foram avaliados. Ambos os grupos realizaram o Teste Timed Up and Go (TUG) e andaram sobre uma superfície rígida e uma complacente, enquanto dados cinemáticos foram registrados. RESULTADOS: O GMI levou mais tempo para completar o TUG quando comparado ao GIJ (F1,14=5,18; p=0,04). A velocidade, o comprimento do passo e o deslocamento vertical do pé foram similares entre os grupos, e ambos foram mais lentos (F1,14=5,64; p=0.03) ao andar sobre a superfície complacente. A amplitude de movimento do joelho e do quadril no plano sagital (F1,14=191,9; p<0,001 e F1,14=36,4, p<0,001, respectivamente) aumentaram na superfície complacente, mas nenhuma diferença entre os grupos foi encontrada. O deslocamento do tronco superior no plano frontal foi similar entre os grupos (F1,14=2,43; p=0,14) e condições (F1,14=1,15; p=0,3). O GMI teve maior deslocamento do segmento da pelve no plano frontal do que o GIJ (F1,14=4,9; p=0,04), principalmente na superfície complacente. CONCLUSÃO: Indivíduos muito idosos são mais lentos no TUG e apresentam maior deslocamento do segmento pélvico na superfície complacente. Tarefas e/ou ambientes mais desafiadores deveriam ser usados para avaliação da marcha e intervenção em idosos com risco de quedas.

Gait characteristics of younger-old and older-old adults walking overground and on a compliant surface.

BACKGROUND: Walking across unstable surfaces disturbs normal stability and efficient strategies must be used to avoid falls. This study identified age-related changes in gait during unstable surface walking. METHOD: Eight healthy younger-old adults (YOG, mean age, 68.6 years) and eight healthy older-old adults (OOG, mean age, 82.1 years) were assessed. Both groups performed the Timed Up and Go Test (TUG) and walked on a rigid and on a compliant surface while kinematic data were obtained. RESULTS: The OOG needed more time to complete the TUG test compared to YOG (F1,14=5.18; p=0.04). The gait speed, stride length and vertical displacement of the foot were similar for both groups, but they were slower (F1,14=5.64; p=0.03) when walking on the compliant surface. The knee and hip range of motion on the sagittal plane (F1,14=191.9; p<0.001 and F1,14=36.4, p<0,001, respectively) increased on the complaint surface but no group effect was found. The displacement of upper trunk on the frontal plane was similar between groups (F1,14=2.43; p=0.14) and conditions (F1,14=1.15; p=0.3). The OOG had greater displacement of the pelvic segment on the frontal plane than the YOG (F1,14=4.9; p=0.04) mainly for the complaint surface. CONCLUSIONS: Older-old individuals have slower TUG test and greater displacement of the pelvic segment on a compliant surface. More challenging tasks and/or environment should be used for gait assessment and intervention of older adults with risk of falls.

Motor asymmetry reduction in older adults.

While cerebral lateralization has previously been well documented for many neurobehavioral functions, recent research has shown that as people age, formerly lateralized processes recruit more symmetric patterns of neural activity. Such findings provide the foundation for the model of hemispheric asymmetry reduction in older adults, or "HAROLD"[4]. Previous studies that have measured reaction time and movement time have suggested that aging does not affect manual asymmetries. However, whether these findings can be extended to kinematic variables associated with motor coordination remains largely unknown. The purpose of the current study is to determine whether asymmetries in intralimb coordination are also reduced during the aging process. We examined multidirectional reaching in two different right handed age groups, a younger group from 20 to 40 years of age, and an older group, from 60 to 80 years of age. Measures of final position accuracy, precision, and trajectory linearity showed robust asymmetries between the left and right arm groups of young adults. However, the trajectories and accuracies of the older subjects were symmetric, such that our dependent measures were not significantly different between the right and left arm groups. Our findings extend the HAROLD model to motor behavior, suggesting that aging results in decrements in motor lateralization.

Differential influence of vision and proprioception on control of movement distance.

The purpose of this study was to investigate the contribution of proprioceptive and visual information about initial limb position in controlling the distance of rapid, single-joint reaching movements. Using a virtual reality environment, we systematically changed the relationship between actual and visually displayed hand position as subjects' positioned a cursor within a start circle. No visual feedback was given during the movement. Subjects reached two visual targets (115 and 125 degrees elbow angle) from four start locations (90, 95, 100, and 105 degrees elbow angle) under four mismatch conditions (0, 5, 10, or 15 degrees). A 2 x 4 x 4 ANOVA enabled us to ask whether the subjects controlled the movement distance in accord with the virtual, or the actual hand location. Our results indicate that the movement distance was mainly controlled according to the virtual start location. Whereas distance modification was most extensive for the closer target, analysis of acceleration profiles revealed that, regardless of target position, visual information about start location determined the initial peak in tangential hand acceleration. Peak acceleration scaled with peak velocity and movement distance, a phenomenon termed "pulse-height" control. In contrast, proprioceptive information about actual hand location determined the duration of acceleration, which also scaled with peak velocity and movement distance, a phenomenon termed "pulse-width" control. Because pulse-height and pulse-width mechanisms reflect movement planning and sensory-based corrective processes, respectively, our current findings indicate that vision is used primarily for planning movement distance, while proprioception is used primarily for online corrections during rapid, unseen movements toward visual targets.

Interlimb transfer of load compensation during rapid elbow joint movements.

Previous research has shown that training of a novel task can improve subsequent performance in the opposite arm owing to anticipation of the previously learned task conditions. Interestingly, we recently reported preliminary evidence that such transfer might also include modulation of feedback-mediated responses. We now test interlimb transfer of load compensation responses, measured through kinematic and EMG recordings during rapid 20 degrees elbow flexion movements. Two subject groups, LR and RL, each comprising six right-handed subjects, first performed using either the left (LR) or right (RL) arm, followed by opposite arm performance. After 30 trials of consistent performance, five random trials within a background of 50 trials were loaded with a 2-kg mass prior to the "go" signal. We compared load compensation responses for naive performance with those following opposite arm exposure. Under naive conditions, the resulting load compensation responses began about 50 ms following movement onset, and were substantially more effective for the nondominant arm. Opposite arm exposure substantially improved the accuracy of only dominant arm responses. This, however, did not occur through changes in the short latency components of the load compensation response. Instead, changes in muscle activities, associated with interlimb transfer, began some 150 ms following movement onset. We expect that these changes represent transfer in the "volitional" component of the load compensation response. Because the shorter latency response was unaffected by opposite arm exposure, modulation of this component likely requires prior experience with limb specific effectors.

Nondominant arm advantages in load compensation during rapid elbow joint movements.

This study was designed to examine interlimb asymmetries in responding to unpredictable changes in inertial loads, which have implications for our understanding of the neural mechanisms underlying handedness. Subjects made repetitive single joint speed constrained 20 degrees elbow flexion movements, while the arm was supported on a horizontal, frictionless, air-jet system. On random trials, a 2-kg mass was attached to the arm splint prior to the "go" signal. Subjects were not given explicit information about the mass prior to movement nor were they able to view their limb or the mass. Accordingly, muscle activity, recorded prior to peak tangential finger acceleration, was the same for loaded and baseline trials. After this point, substantial changes in muscle activity occurred. In both limbs, the load compensation response was associated with a reduction in extensor muscle activity, resulting in a prolonged flexion phase of motion. For the nondominant arm, this resulted in effective load compensation, such that no differences in final position accuracy occurred between loaded and baseline trials. However, the dominant arm response also included a considerable increase in flexor muscle activity. This substantially prolonged the flexor acceleration phase of motion, relative to that of the nondominant arm. As a result, the dominant arm overcompensated the effects of the load, producing a large and systematic overshoot of final position. These results indicate more effective load compensation responses for the nondominant arm; supporting a specialized role of the nondominant arm/hemisphere system in sensory feedback mediated error correction mechanisms. The results also suggest that specialization of the dominant arm system for controlling limb and task dynamics is specifically related to feedforward control mechanisms.

Effects of altering initial position on movement direction and extent.

The purpose of this study was to examine the relative influence of initial hand location on the direction and extent of planar reaching movements. Subjects performed a horizontal-plane reaching task with the dominant arm supported above a table top by a frictionless air-jet system. A start circle and a target were reflected from a horizontal projection screen onto a horizontally positioned mirror, which blocked the subject's view of the arm. A cursor, representing either actual or virtual finger location, was only displayed between each trial to allow subjects to position the cursor in the start circle. Prior to occasional "probe trials," we changed the start location of the finger relative to the cursor. Subjects reported being unaware of the discrepancy between cursor and finger. Our results indicate that regardless of initial hand location, subjects did not alter the direction of movement. However, movement distance was systematically adjusted in accord with the baseline target position. Thus when the hand start position was perpendicularly displaced relative to the target direction, neither the direction nor the extent of movement varied relative to that of baseline. However, when the hand was displaced along the target direction, either anterior or posterior, movements were made in the same direction as baseline trials but were shortened or lengthened, respectively. This effect was asymmetrical such that movements from anterior displaced positions showed greater distance adjustment than those from posterior displaced positions. Inverse dynamic analysis revealed substantial changes in elbow and shoulder muscle torque strategies for both right/left and anterior/posterior pairs of displacements. In the case of right/left displacements, such changes in muscle torque compensated changes in limb configuration such that movements were made in the same direction and to the same extent as baseline trials. Our results support the hypothesis that movement direction is specified relative to an origin at the current location of the hand. Movement extent, on the other hand, appears to be affected by the workspace learned during baseline movement experience.

Handedness: dominant arm advantages in control of limb dynamics.

Recent findings from our laboratory suggest that a major factor distinguishing dominant from nondominant arm performance is the ability by which the effects of intersegmental dynamics are controlled by the CNS. These studies indicated that the dominant arm reliably used more torque-efficient patterns for movements made with similar speeds and accuracy than nondominant arm movements. Whereas, nondominant hand-path curvatures systematically varied with the amplitude of the interaction torques transferred between the segments of the moving limb, dominant hand-path curvatures did not. However, our previous studies did not distinguish whether dominant arm coordination advantages emerged from more effective control of dynamic factors or were simply a secondary effect of planning different kinematics. The purpose of this study was to further investigate interlimb differences in coordination through analysis of inverse dynamics and electromyography recorded during the performance of reaching movements. By controlling the amplitude of intersegmental dynamics in the current study, we were able to assess whether systematic differences in torque-efficiency exist, even when differences in hand-path shape were minimal. Subject's arms were supported in the horizontal plane by a frictionless air-jet system and were constrained to movements about the shoulder and elbow joints. Two targets were designed, such that the interaction torques elicited at the elbow were either large or small. Our results showed that the former produced large differences in hand-path curvature, whereas the latter did not. Additionally, the movements with small differences in hand-path kinematics showed substantial differences in torque patterns and corresponding EMG profiles which implied a more torque-efficient strategy for the dominant arm. In view of these findings we propose that distinct neural control mechanisms are employed for dominant and nondominant arm movements.