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Neuromotor therapy after spinal cord or brain injury often attempts to utilize activity-dependent plasticity to promote functional recovery. Neuromuscular electrical stimulation that activates paralyzed or paretic muscles may enhance passive assistance therapy by activating more muscle mass and enriching the sensory pattern with appropriately timed muscle spindle activation. To enable studies of activity-dependent plasticity, a rodent model for stimulation-assisted locomotor therapy was developed previously. To be effective, however, such a system must allow lengthy sessions of repetitive movements. In this study, we implemented an adaptive pattern generator/pattern shaper (PG/PS) control system for a rodent model of neuromotor therapy and evaluated its ability to generate accurate and repeatable hip movements in lengthy sessions by adjusting the activation patterns of an agonist/antagonist muscle pair. In 100-cycle movement trials, the PG/PS control system provided excellent movement tracking (< 10% error), but stimulation levels steadily increased to account for muscle fatigue. In trials using an intermittent movement paradigm (100 sets of five-cycle bouts interspersed by 20-s rest periods), excellent performance ( Index Terms--Activity-dependent plasticity, adaptive neural network control, intramuscular electrodes, locomotor therapy, neuromuscular stimulation, spinal cord injury (SCI).

A neural network control system has been designed for the control of cyclic movements in Functional Neuromuscular Stimulation (FNS) systems. The design directly addresses three major problems in FNS control systems: customization of control system parameters for a particular individual, adaptation during operation to account for changes in the musculoskeletal system, and attaining resistance to mechanical disturbances. The control system was implemented by a two-stage neural network that utilizes a combination of adaptive feedforward and feedback control techniques. A new learning algorithm was developed to provide rapid customization and adaptation. The control system was evaluated in a series of studies on a computer simulated musculoskeletal model. The model of electrically stimulated muscle used in the study included nonlinear recruitment, linear dynamics, and multiplicative nonlinear torque-angle and torque-velocity scaling factors. The skeletal model consisted of a one-segment planar system with passive constraints on joint movement. Results of the evaluation have demonstrated that the control system can provide automated customization of the feedforward controller parameters for a given musculoskeletal system. It can account for changes in the musculoskeletal system by adapting the feedforward controller parameters on-line and it can resist the effects of mechanical disturbances. These results suggest that this design may be suitable for the control of FNS systems and other dynamic systems.

This study evaluated an adaptive control system (the PG/PS control system [2]) that had been designed for generating cyclic movements using functional neuromuscular stimulation (FNS). Extensive simulations using computer-based models indicated that a broad range of control system parameter values performed well across a diverse population of model systems. The fact that manual tuning is not required for each individual makes this control system particularly attractive for implementation in FNS systems outside of research laboratories. Index Terms--Adaptive control, cyclic movements, functional neuromuscular stimulation, neural networks, sensitivity analysis.

Decoding motor intent from recorded neural signals is essential for the development of effective neural-controlled prostheses. To facilitate the development of online decoding algorithms we have developed a software platform to simulate neural motor signals recorded with peripheral nerve electrodes, such as longitudinal intrafascicular electrodes (LIFEs). The simulator uses stored motor intent signals to drive a pool of simulated motoneurons with various spike shapes, recruitment characteristics, and firing frequencies. Each electrode records a weighted sum of a subset of simulated motoneuron activity patterns. As designed, the simulator facilitates development of a suite of test scenarios that would not be possible with actual data sets because, unlike with actual recordings, in the simulator the individual contributions to the simulated composite recordings are known and can be methodically varied across a set of simulation runs. In this manner, the simulation tool is suitable for iterative development of real-time decoding algorithms prior to definitive evaluation in amputee subjects with implanted electrodes. The simulation tool was used to produce data sets that demonstrate its ability to capture some features of neural recordings that pose challenges for decoding algorithms. [ABSTRACT FROM AUTHOR]

Neuromotor therapy after spinal cord or brain injury often attempts to utilize activity-dependent plasticity to promote functional recovery. Neuromuscular electrical stimulation that activates paralyzed or paretic muscles may enhance passive assistance therapy by activating more muscle mass and enriching the sensory pattern with appropriately timed muscle spindle activation. To enable studies of activity-dependent plasticity, a rodent model for stimulation-assisted locomotor therapy was developed previously. To be effective, however, such a system must allow lengthy sessions of repetitive movements. In this study, we implemented an adaptive pattern generator/pattern shaper (PG/PS) control system for a rodent model of neuromotor therapy and evaluated its ability to generate accurate and repeatable hip movements in lengthy sessions by adjusting the activation patterns of an agonist/antagonist muscle pair. In 100-cycle movement trials, the PG/PS control system provided excellent movement tracking (<10% error), but stimulation levels steadily increased to account for muscle fatigue. In trials using an intermittent movement paradigm (100 sets of five-cycle bouts interspersed by 20-s rest periods), excellent performance (<8% error) was also observed with less stimulation, thus indicating reduced muscle fatigue. These results demonstrate the ability of the PG/PS control system to utilize an agonist/antagonist muscle pair to control movement at a joint in a rodent model. The demonstration of repeatable movements over lengthy intermittent sessions suggests that it may be well suited to provide efficient neuromotor therapy. [ABSTRACT FROM AUTHOR]

This study investigated the effects of altering foot placement on the strategies used by able-bodied subjects to perform reaching tasks while standing. The motivation for this study was to consider the results in the context of a person with a spinal cord injury using a functional neuromuscular stimulation (FNS) system to stand while reaching. Three foot placement conditions were compared as subjects reached to the left, right, and center. Centers of pressure (COP), joint angles, and joint moments were calculated as postural parameters using force platform and video marker data. Side-by-side and wide foot placements resulted in similar postural parameters. In contrast, the modified tandem stance (feet spaced at pelvic width with one foot shifted forward) resulted in anterior/posterior COP excursions that were larger in magnitude and more consistent across reach directions when compared to the other foot placement conditions. Furthermore, the movement patterns used during the tandem stance were more consistent and may be more readily achievable with FNS than the movement patterns utilized with the side-by-side and wide stances. These results suggest that the modified tandem stance may enhance the functionality of FNS standing systems and may also be useful in other standing rehabilitation programs. Index TermsαBiomechanics; kinematics; neuromuscular stimulation; posture; spinal-cord injury (SCI). [ABSTRACT FROM AUTHOR]

Discusses the use of a functional neuromuscular stimulation systems to activate paralyzed muscles. Evaluation of the pattern generator/pattern shaper adaptive controller on subjects with spinal cord injuries; Changes in system properties due to fatigue.

Presents a novel demonstration of real-time dynamic interaction between an oscillatory spinal cord and electronic hardware that mimics the spinal motor pattern generating circuitry. Examination of the intrinsic dynamics of neural circuitry; Provision of a powerful means of restoring complex neuromotor function using neuroprostheses; Production of rhythmic motor output for controlling locomotion.