Evaluation of a noninvasive command scheme for upper-limb prostheses in a virtual reality reach and grasp task.

C5/C6 tetraplegic patients and transhumeral amputees may be able to use voluntary shoulder motion as command signals for a functional electrical stimulation system or transhumeral prosthesis. Stereotyped relationships, termed "postural synergies," among the shoulder, forearm, and wrist joints emerge during goal-oriented reaching and transport movements as performed by able-bodied subjects. Thus, the posture of the shoulder can potentially be used to infer the desired posture of the elbow and forearm joints during reaching and transporting movements. We investigated how well able-bodied subjects could learn to use a noninvasive command scheme based on inferences from these postural synergies to control a simulated transhumeral prosthesis in a virtual reality task. We compared the performance of subjects using the inferential command scheme (ICS) with subjects operating the simulated prosthesis in virtual reality according to complete motion tracking of their actual arm and hand movements. Initially, subjects performed poorly with the ICS but improved rapidly with modest amounts of practice, eventually achieving performance only slightly less than subjects using complete motion tracking. Thus, inferring the desired movement of distal joints from voluntary shoulder movements appears to be an intuitive and noninvasive approach for obtaining command signals for prostheses to restore reaching and grasping functions.

Changes in wrist muscle activity with forearm posture: implications for the study of sensorimotor transformations.

The primate wrist is an ideal model system for studying the reference frames in which movements are coded within the central nervous system, as a simple rotation of the forearm allows dissociation between extrinsic and body-referenced coordinates. Important information regarding coordinate frame transformations has been obtained using this system, particularly from studies involving extracellular cortical and spinal recordings from monkeys. Because preferred directions of muscle use were reported to rotate by less than half of the joint rotation, the system was considered to dissociate three reference frames: extrinsic (direction of movement in space), muscle (activity of muscles), and joint (angle of the wrist joint). However, given the relatively minor changes in reported muscle biomechanics with human forearm rotation, the reported distinction between joint space and muscle space is surprisingly large. Here, we reassessed patterns of wrist muscle activity with changes in forearm posture in humans, during an isometric force-aiming task with a device that enabled stringent control of the musculoskeletal configuration. Results show that the preferred directions for wrist muscle activation closely follow forearm orientation (i.e., by 88%). Control experiments confirmed this, whether the hand was clamped passively by a device or grasped a handle. Furthermore, the remaining 12% discrepancy between intended changes in wrist orientation and muscle use also occurred for muscle-pulling directions obtained by intramuscular electrical stimulation. The findings prompt reconsideration of data based on the previously reported dissociation between joint space and muscle space and have critical implications for future investigations of sensorimotor transformations and their adaptation using the wrist.

Real-time animation software for customized training to use motor prosthetic systems.

Research on control of human movement and development of tools for restoration and rehabilitation of movement after spinal cord injury and amputation can benefit greatly from software tools for creating precisely timed animation sequences of human movement. Despite their ability to create sophisticated animation and high quality rendering, existing animation software are not adapted for application to neural prostheses and rehabilitation of human movement. We have developed a software tool known as MSMS (MusculoSkeletal Modeling Software) that can be used to develop models of human or prosthetic limbs and the objects with which they interact and to animate their movement using motion data from a variety of offline and online sources. The motion data can be read from a motion file containing synthesized motion data or recordings from a motion capture system. Alternatively, motion data can be streamed online from a real-time motion capture system, a physics-based simulation program, or any program that can produce real-time motion data. Further, animation sequences of daily life activities can be constructed using the intuitive user interface of Microsoft's PowerPoint software. The latter allows expert and nonexpert users alike to assemble primitive movements into a complex motion sequence with precise timing by simply arranging the order of the slides and editing their properties in PowerPoint. The resulting motion sequence can be played back in an open-loop manner for demonstration and training or in closed-loop virtual reality environments where the timing and speed of animation depends on user inputs. These versatile animation utilities can be used in any application that requires precisely timed animations but they are particularly suited for research and rehabilitation of movement disorders. MSMS's modeling and animation tools are routinely used in a number of research laboratories around the country to study the control of movement and to develop and test neural prostheses for patients with paralysis or amputations.

MSMS software for VR simulations of neural prostheses and patient training and rehabilitation.

In the increasingly complex prosthetic limbs for upper extremity amputees, more mechanical degrees of freedom are combined with various neural commands to produce versatile human-like movements. Development, testing, and fitting of such neural prosthetic systems and training patients to control them effectively are complex processes that cannot be performed efficiently or safely by ad hoc and trial-and-error approaches. We have developed a software tool known as MSMS to enable researchers and engineers to simulate the movement of these neural prostheses and evaluate their performance before they are built and to train the patients in virtual simulation environments to operate their prostheses before receiving them. Further, MSMS facilitates development of interactive virtual reality applications for training, rehabilitation, and treatment of patients suffering from movement disorders.

Neuromuscular and biomechanical factors codetermine the solution to motor redundancy in rhythmic multijoint arm movement.

How the CNS deals with the issue of motor redundancy remains a central question for motor control research. Here we investigate the means by which neuromuscular and biomechanical factors interact to resolve motor redundancy in rhythmic multijoint arm movements. We used a two-df motorized robot arm to manipulate the dynamics of rhythmic flexion-extension (FE) and supination-pronation (SP) movements at the elbow-joint complex. Participants were required to produce rhythmic FE and SP movements, either in isolation, or in combination (at the phase relationship of their choice), while we recorded the activity of key bi-functional muscles. When performed in combination, most participants spontaneously produced an in-phase pattern of coordination in which flexion is synchronised with supination. The activity of the Biceps Brachii (BB), the strongest arm muscle which also has the largest moment arms in both flexion and supination was significantly higher for FE and SP performed in combination than in isolation, suggesting optimal exploitation of the mechanical advantage of this muscle. In a separate condition, participants were required to produce a rhythmic SP movement while a rhythmic FE movement was imposed by the motorized robot. Simulations based upon a musculoskeletal model of the arm demonstrated that in this context, the most efficient use of the force-velocity relationship of BB requires that an anti-phase pattern of coordination (flexion synchronized with pronation) be produced. In practice, the participants maintained the in-phase behavior, and BB activity was higher than for SP performed in isolation. This finding suggests that the neural organisation underlying the exploitation of bifunctional muscle properties, in the natural context, constrains the system to maintain the "natural" coordination pattern in an altered dynamic environment, even at the cost of reduced biomechanical efficiency. We suggest an important role for afference from the imposed movement in promoting the "natural" pattern. Practical implications for the emerging field of robot-assisted therapy and rehabilitation are briefly mentioned.

Model-based development of neural prostheses for movement.

Neural prostheses for restoration of limb movement in paralyzed and amputee patients tend to be complex systems. Subjective intuition and trial-and-error approaches have been applied to the design and clinical fitting of simple systems with limited functionality. These approaches are time consuming, difficult to apply in larger scale, and not applicable to limbs under development with more anthropomorphic motion and actuation. The field of neural prosthetics is in need of more systematic methods, including tools that will allow users to develop accurate models of neural prostheses and simulate their behavior under various conditions before actual manufacturing or clinical application. Such virtual prototyping would provide an efficient and safe test-bed for narrowing the design choices and tuning the control parameters before actual clinical application. We describe a software environment that we have developed to facilitate the construction and modification of accurate mathematical models of paralyzed and prosthetic limbs and simulate their movement under various neural control strategies. These simulations can be run in real time with a stereoscopic display to enable design engineers and prospective users to evaluate a candidate neural prosthetic system and learn to operate it before actually receiving it.

A virtual reality environment for designing and fitting neural prosthetic limbs.

Building and testing novel prosthetic limbs and control algorithms for functional electrical stimulation (FES) is expensive and risky. Here, we describe a virtual reality environment (VRE) to facilitate and accelerate the development of novel systems. In the VRE, subjects/patients can operate a simulated limb to interact with virtual objects. Realistic models of all relevant musculoskeletal and mechatronic components allow the development of entire prosthetic systems in VR before introducing them to the patient. The system is used both by engineers as a development tool and by clinicians to fit prosthetic devices to patients.

The effects of training set on prediction of elbow trajectory from shoulder trajectory during reaching to targets.

Patients with transhumeral amputations and C5/C6 quadriplegia may be able to use voluntary shoulder motion as command signals for powered prostheses and functional electrical stimulation, respectively. Spatio-temporal synergies exist for goal oriented reaching movements between the shoulder and elbow joints in able bodied subjects. We are using a multi-layer perceptron neural network to discover and embody these synergies. Such a network could be used as a high level functional electrical stimulation (FES) controller that could predict elbow joint kinematics from the voluntary movements of the shoulder joint. Counter-intuitively, a well-chosen reduced data set for training the network resulted in better performance than use of the whole data set against which the predictions of the network were evaluated.

Fuzzy logic control of FES rowing exercise in paraplegia.

An indoor personal rowing machine (Concept 2 Inc., Morrisville, VT) has been modified for functional electrical stimulation assisted rowing exercise in paraplegia. To successfully perform the rowing maneuver, the voluntarily controlled upper body movements must be coordinated with the movements of the electrically stimulated paralyzed legs. To achieve such coordination, an automatic controller was developed that employs two levels of hierarchy. A high level finite state controller identifies the state or phase of the rowing motion and activates a low-level state-dedicated fuzzy logic controller (FLC) to deliver the electrical stimulation to the paralyzed leg muscles. A pilot study with participation of two paraplegic volunteers showed that FLC spent less muscle energy, and produced smoother rowing maneuvers than the existing On-Off constant-level stimulation controller.

Development of an indoor rowing machine with manual FES controller for total body exercise in paraplegia.

Concept 2 indoor rowing machine (Concept 2 Inc., USA) was modified for functional electrical stimulation (FES) rowing exercise in paraplegia. A new seating system provides trunk stability and constrains the leg motion to the sagittal plane. A 4-channel electrical stimulator activates the quadriceps and hamstrings in Drive and Recovery phases of the rowing cycle, respectively. Two force-sensing resistors (FSR) on the handle measure the thumb press as the command signal to the electrical stimulator. Optical encoders measure the positions of the seat and handle during rowing. To synchronize the voluntarily controlled upper body movement with the FES controlled leg movement, a novel manual control system was developed. It uses the voluntary thumb presses to control the timing of the stimulation to the paralyzed leg muscles. The manual control system was intuitive and easy to learn and resulted in well-coordinated rowing. Evaluation of the modified rower by paraplegic volunteers showed that it is effective, safe, and affordable exercise alternative for paraplegics.

The importance of biomechanics.

When neuroscientists gather to discuss "Movement and Sensation", they tend to discuss neurons rather than muscles and bones. Neurons may be more interesting, but their roles in motor control depend on the mechanical properties of the system to be controlled. Understanding of those properties has been surprisingly elusive, despite the well-developed disciplines of biomechanics and muscle physiology. Each experimental field has its favorite, often unique preparation. Mathematical models range in scale from individual cross-bridges to articulated limbs, usually written in different computer languages. The shortcomings of such fragmented knowledge become particularly apparent when biomedical engineers must design safe and effective control systems for real limbs, such as for functional electrical stimulation (FES) of reach and grasp in quadriplegic patients. We are addressing the question of how to model neuromusculoskeletal systems so that they are sufficiently complete, valid and accessible to be useful in both basic and applied sensorimotor research.

Automatic Finite State Control of FES-Assisted Indoor Rowing Exercise after Spinal Cord Injury.

We modified a commercial indoor rowing machine (Concept 2 Inc., Morrisville, NJ, USA) for a functional electrical stimulation (FES) assisted indoor rowing exercise in which the rowers must repeatedly press the two switches on the handle that stimulate their paralyzed leg muscles. The objective of this study was to automate the delivery of electrical stimulation to prevent potential repetitive strain injuries and to expand the user base to clients with impaired hand function. The modifications for development of the FES rowing machine and clinical trials were all performed in the University of Alberta. A new controller was developed to automatically control the electrical stimulation of the paralyzed leg muscles to perform the lower extremity part of the rowing maneuver while the subject voluntarily performed the upper body part of the maneuver. Two paraplegic users of the older manual control system tested the new automatic controller. The automatic FES controller spent more electrical stimulation per rowing cycle but it did not require repetitive thumb presses, required less concentration, and was preferred by the clients. We conclude FES rowing with the new automatic controller was easier and safer and expanded the user base of the FES rowing exercise to those with affected hand.