Cervical spinal cord injury can disrupt connections between the brain respiratory network and the... more Cervical spinal cord injury can disrupt connections between the brain respiratory network and the respiratory muscles which can lead to partial or complete loss of ventilatory control and require ventilatory assistance. Unlike current open-loop technology, a closed-loop diaphragmatic pacing system could overcome the drawbacks of manual titration as well as respond to changing ventilation requirements. We present an original bio-inspired assistive technology for real-time ventilation assistance, implemented in a digital configurable Field Programmable Gate Array (FPGA). The bio-inspired controller, which is a spiking neural network (SNN) inspired by the medullary respiratory network, is as robust as a classic controller while having a flexible, low-power and low-cost hardware design. The system was simulated in MATLAB with FPGA-specific constraints and tested with a computational model of rat breathing; the model reproduced experimentally collected respiratory data in eupneic animals. The open-loop version of the bio-inspired controller was implemented on the FPGA. Electrical test bench characterizations confirmed the system functionality. Open and closed-loop paradigm simulations were simulated to test the FPGA system real-time behavior using the rat computational model. The closed-loop system monitors breathing and changes in respiratory demands to drive diaphragmatic stimulation. The simulated results inform future acute animal experiments and constitute the first step toward the development of a neuromorphic, adaptive, compact, low-power, implantable device. The bio-inspired hardware design optimizes the FPGA resource and time costs while harnessing the computational power of spike-based neuromorphic hardware. Its real-time feature makes it suitable for in vivo applications.
Decoding motor intent from recorded neural signals is essential for the development of effective ... more 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 There is growing interest in developing prosthetic limbs capable of providing sensory fe... more ABSTRACT There is growing interest in developing prosthetic limbs capable of providing sensory feedback to amputees. The development of such advanced systems requires accurate, quantitative assessment of the sensation perceived by the amputee. We have designed and fabricated robust, devices to track and record hand-opening distance and pinch force during a series of structured tasks performed by unilateral amputees using their intact hand to mirror perceived sensation in the amputated limb. For hand-opening distance measurement, the subject's thumb and forefinger are coupled to linear potentiometers. While subjects open and close their hand freely, the distance between the thumb and forefinger is estimated in real time by recording the voltage output. For pinch force measurement, a commercially-available mini compression load cell is mounted on a custom-designed aluminum assembly that is adjustable to enable measurement at different hand-opening distances. The load cell generates a voltage signal proportional to the applied pinch force. Calibration was accomplished by applying incremental forces using a compression load testing device while monitoring the voltage output. These measurements will help to quantify the amputee's perception of hand-opening and pinch force and thereby serve towards developing a subject-specific sensor-stimulation map that can be programmed into an advanced prosthesis.
Proceedings of International Conference on Neural Networks (ICNN'97), 1997
ABSTRACT Neural circuitry within the spinal cord of the lamprey, a primitive vertebrate, can gene... more ABSTRACT Neural circuitry within the spinal cord of the lamprey, a primitive vertebrate, can generate self-sustained oscillations for locomotion (swimming). This pattern generator can be modeled as a chain of oscillatory unit pattern generator segments which exhibit behavior depending on the parameter values in the network. Here, the authors present the results of a simulation study of an analog electronic circuit which mimics the behavior of the biological lamprey unit pattern generator. The circuitry mimics a neural network containing 6 neurons with simplified biophysical properties. The analog circuit exhibits symmetric oscillations, asymmetric oscillations, and fixed points, similar to the behavior of the mathematical model of the lamprey. This work is the first in a series of circuits designed to have possible applications in neuroscience research and in the development of artificial locomotor systems
IEEE journal of biomedical and health informatics, Jan 25, 2015
For people with Parkinson's disease (PD), gait and postural impairments can significantly aff... more For people with Parkinson's disease (PD), gait and postural impairments can significantly affect their ability to perform activities of daily living. Presentation of appropriate cues have been shown to improve gait in PD. Based on this, a treadmill-based system and experimental paradigm was developed to determine if people with PD can utilize real-time feedback (RTFB) of step length and back angle (uprightness) to improve gait and posture. Eleven subjects (mean age 65.9 ± 7.6 years) with mild to moderate PD (Hoehn and Yahr stage I-III) were evaluated regarding their ability to successfully utilize RTFB of back angle or step length during quiet standing and treadmill walking tasks during a single session in their medication-on state. Changes in back angle and step length due to feedback were compared using Friedman nonparametric tests with Wilcoxon Signed-Rank tests for post hoc comparisons. Improvements in uprightness were observed as an increase in back angle during quiet stand...
When using functional neuromuscular stimulation for standing, altering foot placement may result ... more When using functional neuromuscular stimulation for standing, altering foot placement may result in postural benefits during activities of daily living. To be useful, these foot placements must first be stable during quiet standing. Postural parameters were quantified as a function of foot placement during quiet standing for two subjects with spinal cord injury. Force platform and kinematic measurements were taken. With one exception, vertical ground reactions (a measure of hand support) were not dependent upon foot placement. In addition, sacral marker position correlated with centers of pressure in the anterior-posterior direction for all foot placements. The modified tandem stance allowed Subject #2 to more effectively compensate for weakness in his right quadriceps musculature than the other stances. Overall, for these two subjects, standing capability during short, quiet standing trials was not appreciably affected by altering foot placement.
Images of the Twenty-First Century. Proceedings of the Annual International Engineering in Medicine and Biology Society, 1989
ABSTRACT A feedback controller of coronal plane hip angle was implemented in paraplegic subjects ... more ABSTRACT A feedback controller of coronal plane hip angle was implemented in paraplegic subjects using functional neuromuscular stimulation (FNS). In an evaluation based on standard temporal response properties, the feedback-controlled system exhibited substantial improvements when compared to an open-loop system. An evaluation based on subjective clinical observations of the experimental trials indicates that standard control system design criteria may not correspond to desired performance characteristics. Consideration of the clinical ratings and identified system model parameters suggests other design criteria which may be more relevant
Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 1988
ABSTRACT A software structure is described that has been developed for the implementation of feed... more ABSTRACT A software structure is described that has been developed for the implementation of feedback controllers for standing, gait, and stair climbing using functional neuromuscular stimulation (FNS) in paralyzed individuals. The control structure has two levels. The upper level controller monitors the progression of the controlled system through a finite set of allowable states. The occurrence of particular events marks the transition of the system from one state to another. In each state a specified set of lower level controllers is used to achieve certain tasks.< >
[Proceedings 1992] IJCNN International Joint Conference on Neural Networks, 1992
ABSTRACT An adaptive neural network control system has been designed for the purpose of controlli... more ABSTRACT An adaptive neural network control system has been designed for the purpose of controlling cyclic movements of nonlinear dynamic systems with input time delays (as found in functional neuromuscular stimulation). The adaptive feedforward (FF) controller is implemented as a two-stage neural network. The first stage, the pattern generator (PG), generates a cyclic pattern of activity. The signals from the PG are adaptively filtered by the second stage, the pattern shaper (PS). This stage uses modifications to standard artificial neural network learning algorithms to adapt its filter properties. The control system is evaluated in computer simulation on a musculoskeletal model which consists of two muscles acting on a swinging pendulum. The control system provides automated customization of the FF controller parameters for a given musculoskeletal system as well as online adaptation of the FF controller parameters to account for changes in the musculoskeletal system
Proceedings of the First Joint BMES/EMBS Conference. 1999 IEEE Engineering in Medicine and Biology 21st Annual Conference and the 1999 Annual Fall Meeting of the Biomedical Engineering Society (Cat. No.99CH37015), 1999
The lamprey, an eel-like fish, has 100 segments in the spinal cord. Each segment, called the unit... more The lamprey, an eel-like fish, has 100 segments in the spinal cord. Each segment, called the unit Pattern Generator (uPG), is capable of generating self-sustained oscillations for locomotion, i.e. swimming. The authors have designed, built, and tested an electronic circuit model of the uPG using analog VLSI CMOS circuits. Their neuromorphic single-segment model utilizes 6 neurons, 4 excitatory synapses, 8 inhibitory synapses, and 6 tonic synapses with simplified biophysical properties. In this paper, the authors present the experimental results of the chip and compare to the simulated chip behavior. They present the operation under varying conductances, then consider the entrainment of the segment to an external signal with varying frequency and magnitude
IJCNN'99. International Joint Conference on Neural Networks. Proceedings (Cat. No.99CH36339), 1999
ABSTRACT The purpose of this research is to develop an analog VLSI electronic circuit that mimics... more ABSTRACT The purpose of this research is to develop an analog VLSI electronic circuit that mimics the behavior of the biological lamprey spinal cord. The lamprey is an eel-like lower vertebrate with a relatively simple nervous system. The pattern generator for locomotion is distributed along the 100 spinal segments of the lamprey spinal cord and can be treated as a chain of coupled unit pattern generators (uPG) with oscillatory properties. In this work we consider a 4 neuron uPG model. Bifurcation analysis of this model indicates a wide range of behaviors. In addition, a CMOS analog integrated circuit has been designed, fabricated and tested which models the biological lamprey unit pattern generator. Measurement results show that the electronic circuit behavior is qualitatively similar to that of the numerical model
Proceedings of the 25th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (IEEE Cat. No.03CH37439), 2003
The long-term goal of this investigation is to enhance the functional abilities of individuals th... more The long-term goal of this investigation is to enhance the functional abilities of individuals that stand using functional neuromuscular stimulation (FNS). A target-acquisition paradigm was used to evaluate two postural variables, center of pressure (COP) and the position of the pelvis (POP) for the sensing of postural adjustments. These variables were examined under two different foot placements: normal and modified tandem stance. Subjects with spinal cord injury (SCI) stood using FNS and made postural adjustments using voluntary upper body control to move a cursor that represented either their COP or POP to a given target displayed on a monitor. Performance and strategy indexes were compared for four stance conditions. Results indicate that the POP feedback provided improved quality of control for many movement directions. Measurements of reaction forces at the hands did not indicate consistent changes across stance conditions. When using the POP feedback, subjects effectively utilized a load/unload strategy in which weight was shifted from one foot to the other in order to execute the posture shift. Thus, sensing and controlling the translation of the pelvis may prove to be a useful approach to enhance the functionality of FNS standing systems.
42nd Midwest Symposium on Circuits and Systems (Cat. No.99CH36356), 2000
ABSTRACT We have designed, built, and tested a neuromorphic model of the lamprey unit pattern gen... more ABSTRACT We have designed, built, and tested a neuromorphic model of the lamprey unit pattern generator using analog VLSI CMOS circuits. The lamprey is an eel-like fish with 100 segments in the spinal cord. Our neuromorphic single-segment model utilizes 6 neurons, 4 excitatory synapses, 8 inhibitory synapses, and 6 tonic synapses with simplified biophysical properties. The chip exhibits fixed point and oscillatory behaviors similar to the numerical model of the biological spinal cord
Cervical spinal cord injury can disrupt connections between the brain respiratory network and the... more Cervical spinal cord injury can disrupt connections between the brain respiratory network and the respiratory muscles which can lead to partial or complete loss of ventilatory control and require ventilatory assistance. Unlike current open-loop technology, a closed-loop diaphragmatic pacing system could overcome the drawbacks of manual titration as well as respond to changing ventilation requirements. We present an original bio-inspired assistive technology for real-time ventilation assistance, implemented in a digital configurable Field Programmable Gate Array (FPGA). The bio-inspired controller, which is a spiking neural network (SNN) inspired by the medullary respiratory network, is as robust as a classic controller while having a flexible, low-power and low-cost hardware design. The system was simulated in MATLAB with FPGA-specific constraints and tested with a computational model of rat breathing; the model reproduced experimentally collected respiratory data in eupneic animals. The open-loop version of the bio-inspired controller was implemented on the FPGA. Electrical test bench characterizations confirmed the system functionality. Open and closed-loop paradigm simulations were simulated to test the FPGA system real-time behavior using the rat computational model. The closed-loop system monitors breathing and changes in respiratory demands to drive diaphragmatic stimulation. The simulated results inform future acute animal experiments and constitute the first step toward the development of a neuromorphic, adaptive, compact, low-power, implantable device. The bio-inspired hardware design optimizes the FPGA resource and time costs while harnessing the computational power of spike-based neuromorphic hardware. Its real-time feature makes it suitable for in vivo applications.
Decoding motor intent from recorded neural signals is essential for the development of effective ... more 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 There is growing interest in developing prosthetic limbs capable of providing sensory fe... more ABSTRACT There is growing interest in developing prosthetic limbs capable of providing sensory feedback to amputees. The development of such advanced systems requires accurate, quantitative assessment of the sensation perceived by the amputee. We have designed and fabricated robust, devices to track and record hand-opening distance and pinch force during a series of structured tasks performed by unilateral amputees using their intact hand to mirror perceived sensation in the amputated limb. For hand-opening distance measurement, the subject's thumb and forefinger are coupled to linear potentiometers. While subjects open and close their hand freely, the distance between the thumb and forefinger is estimated in real time by recording the voltage output. For pinch force measurement, a commercially-available mini compression load cell is mounted on a custom-designed aluminum assembly that is adjustable to enable measurement at different hand-opening distances. The load cell generates a voltage signal proportional to the applied pinch force. Calibration was accomplished by applying incremental forces using a compression load testing device while monitoring the voltage output. These measurements will help to quantify the amputee's perception of hand-opening and pinch force and thereby serve towards developing a subject-specific sensor-stimulation map that can be programmed into an advanced prosthesis.
Proceedings of International Conference on Neural Networks (ICNN'97), 1997
ABSTRACT Neural circuitry within the spinal cord of the lamprey, a primitive vertebrate, can gene... more ABSTRACT Neural circuitry within the spinal cord of the lamprey, a primitive vertebrate, can generate self-sustained oscillations for locomotion (swimming). This pattern generator can be modeled as a chain of oscillatory unit pattern generator segments which exhibit behavior depending on the parameter values in the network. Here, the authors present the results of a simulation study of an analog electronic circuit which mimics the behavior of the biological lamprey unit pattern generator. The circuitry mimics a neural network containing 6 neurons with simplified biophysical properties. The analog circuit exhibits symmetric oscillations, asymmetric oscillations, and fixed points, similar to the behavior of the mathematical model of the lamprey. This work is the first in a series of circuits designed to have possible applications in neuroscience research and in the development of artificial locomotor systems
IEEE journal of biomedical and health informatics, Jan 25, 2015
For people with Parkinson's disease (PD), gait and postural impairments can significantly aff... more For people with Parkinson's disease (PD), gait and postural impairments can significantly affect their ability to perform activities of daily living. Presentation of appropriate cues have been shown to improve gait in PD. Based on this, a treadmill-based system and experimental paradigm was developed to determine if people with PD can utilize real-time feedback (RTFB) of step length and back angle (uprightness) to improve gait and posture. Eleven subjects (mean age 65.9 ± 7.6 years) with mild to moderate PD (Hoehn and Yahr stage I-III) were evaluated regarding their ability to successfully utilize RTFB of back angle or step length during quiet standing and treadmill walking tasks during a single session in their medication-on state. Changes in back angle and step length due to feedback were compared using Friedman nonparametric tests with Wilcoxon Signed-Rank tests for post hoc comparisons. Improvements in uprightness were observed as an increase in back angle during quiet stand...
When using functional neuromuscular stimulation for standing, altering foot placement may result ... more When using functional neuromuscular stimulation for standing, altering foot placement may result in postural benefits during activities of daily living. To be useful, these foot placements must first be stable during quiet standing. Postural parameters were quantified as a function of foot placement during quiet standing for two subjects with spinal cord injury. Force platform and kinematic measurements were taken. With one exception, vertical ground reactions (a measure of hand support) were not dependent upon foot placement. In addition, sacral marker position correlated with centers of pressure in the anterior-posterior direction for all foot placements. The modified tandem stance allowed Subject #2 to more effectively compensate for weakness in his right quadriceps musculature than the other stances. Overall, for these two subjects, standing capability during short, quiet standing trials was not appreciably affected by altering foot placement.
Images of the Twenty-First Century. Proceedings of the Annual International Engineering in Medicine and Biology Society, 1989
ABSTRACT A feedback controller of coronal plane hip angle was implemented in paraplegic subjects ... more ABSTRACT A feedback controller of coronal plane hip angle was implemented in paraplegic subjects using functional neuromuscular stimulation (FNS). In an evaluation based on standard temporal response properties, the feedback-controlled system exhibited substantial improvements when compared to an open-loop system. An evaluation based on subjective clinical observations of the experimental trials indicates that standard control system design criteria may not correspond to desired performance characteristics. Consideration of the clinical ratings and identified system model parameters suggests other design criteria which may be more relevant
Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 1988
ABSTRACT A software structure is described that has been developed for the implementation of feed... more ABSTRACT A software structure is described that has been developed for the implementation of feedback controllers for standing, gait, and stair climbing using functional neuromuscular stimulation (FNS) in paralyzed individuals. The control structure has two levels. The upper level controller monitors the progression of the controlled system through a finite set of allowable states. The occurrence of particular events marks the transition of the system from one state to another. In each state a specified set of lower level controllers is used to achieve certain tasks.< >
[Proceedings 1992] IJCNN International Joint Conference on Neural Networks, 1992
ABSTRACT An adaptive neural network control system has been designed for the purpose of controlli... more ABSTRACT An adaptive neural network control system has been designed for the purpose of controlling cyclic movements of nonlinear dynamic systems with input time delays (as found in functional neuromuscular stimulation). The adaptive feedforward (FF) controller is implemented as a two-stage neural network. The first stage, the pattern generator (PG), generates a cyclic pattern of activity. The signals from the PG are adaptively filtered by the second stage, the pattern shaper (PS). This stage uses modifications to standard artificial neural network learning algorithms to adapt its filter properties. The control system is evaluated in computer simulation on a musculoskeletal model which consists of two muscles acting on a swinging pendulum. The control system provides automated customization of the FF controller parameters for a given musculoskeletal system as well as online adaptation of the FF controller parameters to account for changes in the musculoskeletal system
Proceedings of the First Joint BMES/EMBS Conference. 1999 IEEE Engineering in Medicine and Biology 21st Annual Conference and the 1999 Annual Fall Meeting of the Biomedical Engineering Society (Cat. No.99CH37015), 1999
The lamprey, an eel-like fish, has 100 segments in the spinal cord. Each segment, called the unit... more The lamprey, an eel-like fish, has 100 segments in the spinal cord. Each segment, called the unit Pattern Generator (uPG), is capable of generating self-sustained oscillations for locomotion, i.e. swimming. The authors have designed, built, and tested an electronic circuit model of the uPG using analog VLSI CMOS circuits. Their neuromorphic single-segment model utilizes 6 neurons, 4 excitatory synapses, 8 inhibitory synapses, and 6 tonic synapses with simplified biophysical properties. In this paper, the authors present the experimental results of the chip and compare to the simulated chip behavior. They present the operation under varying conductances, then consider the entrainment of the segment to an external signal with varying frequency and magnitude
IJCNN'99. International Joint Conference on Neural Networks. Proceedings (Cat. No.99CH36339), 1999
ABSTRACT The purpose of this research is to develop an analog VLSI electronic circuit that mimics... more ABSTRACT The purpose of this research is to develop an analog VLSI electronic circuit that mimics the behavior of the biological lamprey spinal cord. The lamprey is an eel-like lower vertebrate with a relatively simple nervous system. The pattern generator for locomotion is distributed along the 100 spinal segments of the lamprey spinal cord and can be treated as a chain of coupled unit pattern generators (uPG) with oscillatory properties. In this work we consider a 4 neuron uPG model. Bifurcation analysis of this model indicates a wide range of behaviors. In addition, a CMOS analog integrated circuit has been designed, fabricated and tested which models the biological lamprey unit pattern generator. Measurement results show that the electronic circuit behavior is qualitatively similar to that of the numerical model
Proceedings of the 25th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (IEEE Cat. No.03CH37439), 2003
The long-term goal of this investigation is to enhance the functional abilities of individuals th... more The long-term goal of this investigation is to enhance the functional abilities of individuals that stand using functional neuromuscular stimulation (FNS). A target-acquisition paradigm was used to evaluate two postural variables, center of pressure (COP) and the position of the pelvis (POP) for the sensing of postural adjustments. These variables were examined under two different foot placements: normal and modified tandem stance. Subjects with spinal cord injury (SCI) stood using FNS and made postural adjustments using voluntary upper body control to move a cursor that represented either their COP or POP to a given target displayed on a monitor. Performance and strategy indexes were compared for four stance conditions. Results indicate that the POP feedback provided improved quality of control for many movement directions. Measurements of reaction forces at the hands did not indicate consistent changes across stance conditions. When using the POP feedback, subjects effectively utilized a load/unload strategy in which weight was shifted from one foot to the other in order to execute the posture shift. Thus, sensing and controlling the translation of the pelvis may prove to be a useful approach to enhance the functionality of FNS standing systems.
42nd Midwest Symposium on Circuits and Systems (Cat. No.99CH36356), 2000
ABSTRACT We have designed, built, and tested a neuromorphic model of the lamprey unit pattern gen... more ABSTRACT We have designed, built, and tested a neuromorphic model of the lamprey unit pattern generator using analog VLSI CMOS circuits. The lamprey is an eel-like fish with 100 segments in the spinal cord. Our neuromorphic single-segment model utilizes 6 neurons, 4 excitatory synapses, 8 inhibitory synapses, and 6 tonic synapses with simplified biophysical properties. The chip exhibits fixed point and oscillatory behaviors similar to the numerical model of the biological spinal cord
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