Physiologically Based Controller for Generating Overground Locomotion Using Functional Electrical Stimulation

Abstract

The physiological control of stepping is governed both by signals descending from supraspinal systems and by circuitry residing within the lumbosacral spinal cord. The goal of this study was to evaluate the capacity of physiologically based controllers to restore functional overground locomotion after neurological damage, such as spinal cord injury when used in conjunction with functional electrical stimulation. For this purpose we implemented and tested two controllers: 1) an intrinsically timed system that generated a predetermined rhythmic output and 2) a sensory-based system that used feedback signals to make appropriate transitions between the unloaded (flexion) and loaded (extension) phases of the gait cycle. A third controller, a combination of the intrinsically timed and sensory-driven controllers, was implemented and two sessions were conducted to demonstrate the functional advantages of this approach. The controllers were tested in anesthetized cats, implanted with intramuscular electrodes in six major extensor and flexor muscles of the hindlimbs. The cats were partially supported on a sliding trolley that was propelled by the hindlimbs along a 2.5-m instrumented walkway. Ground reaction forces and limb positions were measured by force plates in the walkway and by accelerometers secured to the legs of the cat, respectively. The controllers were used to generate patterns of stimulation that would elicit alternating flexor (swing) and extensor (stance) movements in the hindlimbs. Using either the intrinsically timed or sensory-driven controllers, the cats were able to travel a distance of 2.5 m, taking five to 12 steps. Functional stepping sequences were more easily achieved using the intrinsically timed controller as the result of a lower sensitivity to the selection of initial stimulation parameters. However, unlike the sensory-driven controller, the intrinsically timed controller was unable to adjust to overcome walkway resistance and muscle fatigue. Neither system was consistently able to ensure load-bearing stepping. Therefore we propose the use of a "combined controller" that relies heavily on intrinsic timing but that can be reset based on sensory signals. A combined controller such as this one may provide the best solution for restoring robust overground locomotion after spinal cord injury.

Servo-Controlled Hind-Limb Electrical Stimulation for Short-Term Arterial Pressure Control

“…Intramuscular electrodes used in functional electrical stimulation might be used for HES but further refinements are clearly needed regarding the positioning of electrodes including the depth of implantation. 35,36 In conclusion, we identified the dynamic characteristics of the AP response to acupuncture-like HES and demonstrated that a servo-controlled HES system was able to reduce AP at a prescribed target level. Although further studies are required to identify the mechanism of HES to reduce AP, acupuncture-like HES would be an additional modality to exert a quantitative depressor effect on the cardiovascular system.…”

A Mixed-Signal VLSI System for Producing Temporally Adapting Intraspinal Microstimulation Patterns for Locomotion

“…Previous work utilized IF-THEN rules in a state-space control strategy to produce over-ground walking in a cat model of SCI [31], [32]. Other work has demonstrated that neuromorphic silicon neurons can produce patterned movements with spiking outputs comparable to the biological locomotion central pattern generator (CPG) [33].…”

“…Other work has demonstrated that neuromorphic silicon neurons can produce patterned movements with spiking outputs comparable to the biological locomotion central pattern generator (CPG) [33]. The combination of open and closed-loop control ensures safe transitions between swing and stance with proper supportive force as shown during in vivo experiments and in simulations [31]-[35]. Such a control strategy can be implemented in a system-on-chip as the central processor to a walking prosthesis.…”

The locomotor central pattern generator of the rat spinal cord in vitro is optimally activated by noisy dorsal root waveforms

“…This has been demonstrated via experiments in which FL is recorded in response to trains of square electrical pulses applied in vitro either to a DR (Marchetti et al 2001) or to the cauda equina (Etlin et al 2010) of the isolated spinal cord. These studies have typically replicated the in vivo stimulation paradigms with intramuscular electrodes in cats (Guevremont et al 2007) or with different parameters of peripheral (Selionov et al 2009) or epidural electrical stimuli (Dimitrijevic et al 1998) or transmagnetic stimulation in humans (Gerasimenko et al 2010). In all these cases, however, stimulation was only effective in generating a few oscillatory cycles despite continuous stimulation.…”