Ronald Raymond Riso

Neuro-fuzzy extraction of angular information from muscle afferents for ankle control during standing in paraplegic subjects: an animal model

This paper is part of a project whose aim is the implementation of closed-loop control of ankle angular position during functional electrical stimulation (FES) assisted standing in paraplegic subjects using natural sensory information. Here, a neural fuzzy (NF) model is implemented to extract angular position information from the electroneurographic signals recorded from muscle afferents using cuff electrodes in an animal model. The NF model, named dynamic nonsingleton fuzzy logic system is a Mamdani-like fuzzy system, implemented in the framework of recurrent neural networks. The fuzzification procedure implemented was the nonsingleton technique which has been shown in previous works to be able to take into account the uncertainty in the data. The proposed algorithm was tested in different situations and was able to predict reasonably well the ankle angular trajectories especially for small excursions (as during standing) and when the stimulation sites are far from the registration sites. This suggests it may be possible to use activity from muscle afferents recorded with cuff electrodes for FES closed-loop control of ankle position during quiet standing.

Nerve cuff recordings of muscle afferent activity from tibial and peroneal nerves in rabbit during passive ankle motion

Activity from muscle afferents regarding ankle kinesthesia was recorded using cuff electrodes in a rabbit preparation in which tactile input from the foot was eliminated. The purpose was to determine if such activity can provide information useful in controlling functional electrical stimulation (FES) systems that restore mobility in spinal injured man. The rabbits ankle was passively flexed and extended while the activity of the tibial and peroneal nerves was recorded. Responses to trapezoidal stimulus profiles were investigated for excursions from 10 degrees to 60 degrees using velocities from 5 degrees/s to 30 degrees/s and different initial ankle positions. The recorded signals mainly reflect activity from primary and secondary muscle afferents. Dorsiflexion stretched the ankle extensors and produced velocity dependent activity in the tibial nerve, and this diminished to a tonic level during the stimulus plateau. The peroneal nerve was silent during dorsiflexion, but was activated by stretch of the peroneal muscles during ankle extension. The responses of the two nerves behaved in a reciprocal manner, but exhibited considerable hysteresis, since motion that relaxed the stretch to the driving muscle produced an immediate cessation of the prior stretch induced activity. A noted difference between the tibial and peroneal nerve responses is that the range of joint position change that activated the flexor afferents was greater then for the extensor afferents. Ankle rotation at higher velocities increased the dynamic stretch evoked responses during the stimulus ramp but showed no effect on the tonic activity during the stimulus plateau. Prestretching the muscles by altering the initial position increased the response to the ramp movement, however, for the peroneal nerve, when the prestretch brought the flexor muscles near to their maximal lengths, the response to additional stretch provided by the ramp movement was diminished. The results indicate that the whole nerve recorded muscle afferent activity may be useful for control of FES assisted standing, because it can indicate the direction of rotation of the passively moved ankle joint, along with coarse information regarding the rate of movement and static joint position.

Cognitive feedback for use with FES upper extremity neuroprostheses

The development of two sensory substitutions systems that provide cognitive feedback for FES (functional electrical stimulation) hand-grasp-restoration neuroprostheses is described. One system uses an array of five electrodes to provide machine status information and a spatially encoded representation of the command signal that a quadriplegic individual generates to achieve proportional grasp control. Only one electrode site is active at any given instant, and a second informational channel is superimposed on the spatial position channel by modulating the frequency of the stimulus pulses. The frequency-modulated feedback channel signals six levels of force developed at the finger tips during prehension activities. The second sensory system is an integral part of an implanted FES system and utilizes a single subdermally placed electrode to display machine status information and a five-level frequency code for feedback of the user-generated grasp control signal. The multielectrode feedback system was implemented for laboratory studies using surface-mounted electrodes, although its design will ultimately incorporate subdermal electrodes to provide a highly cosmetic and unencumbering system.<<ETX>>

Long-term Cuff Electrode Recordings from Peripheral Nerves in Animals and Humans

A peripheral nerve contains thousands of nerve fibers, each of them transmitting information, either from the periphery to the central nervous system or from the central nervous system to the periphery. The efferent fibers transmit information to actuators, mainly muscles, whereas afferent fibers transmit sensory information about the state of organs and events, such as muscle length, touch, skin temperature, joint angles, nociception, and several other modalities of sensory information.

Perspectives on the role of afferent signals in control of motor neuroprostheses

K.O. Johnson reviews the architecture and low level neural mechanisms by which the external environment is transduced and encoded into the neural system, summarizing work that correlates neurophysiological and psychophysical testing with isolation of sensory components. The slowly adapting Type I afferent system is responsible for form and texture perception; the rapidly adapting afferent system is responsible for motion perception; and the Pacinian corpuscle system is responsible for vibratory sensation. R.R. Riso reviews the current level of understanding of the major factors to be considered in the design of a functional neuromuscular stimulation (FNS) grasp controller that uses cutaneous sensory feedback to detect slip. The elegant natural control scheme that matches the ratio of grip and lift forces to frictional conditions provides a model for implementing a slip-based control algorithm. D. Popović discusses the possible use of recordings from more proximal peripheral nerves to determine needed information for synthesis of locomotion. The discussion is illustrated with an animal model where rule-based closed-loop control is used for the ankle joint during treadmill locomotion. Neural signals from the tibial and superficial peroneal nerves were employed to substitute for missing afferent input from cutaneous and proprioceptive sensors. The feasibility of more invasive intraneural electrodes for distinguishing sensory from motor information in mixed nerves is considered. M. Koris raises surgical and functional issues relevant to developing clinical FNS systems. C. Van Doren suggests alternative neurophysiological and engineering approaches.

Effect of initial joint position on nerve-cuff recordings of muscle afferents in rabbits

The objective was to characterize nerve-cuff recordings of muscle afferents to joint rotation over a large part of the physiological joint range. This information is needed to develop control strategies for functional electrical stimulation (FES) systems using muscle afferent signals for sensory feedback. Five acute rabbit experiments were performed. Tripolar cuff electrodes were implanted around the tibial and peroneal divisions of the sciatic nerve in the rabbits left leg. The electroneurograms (ENG) were recorded during passive ankle rotation, using a ramp-and-hold profile starting at seven different joint positions (excursion=5/spl deg/, velocity=10/spl deg//s, initial positions 60/spl deg/, 70/spl deg/, 80/spl deg/, 90/spl deg/, 100/spl deg/, 110/spl deg/, and 120/spl deg/). The amplitude of the afferent activity was dependent on the initial joint position. The steady-state sensitivity of both nerve responses increased with increasing joint flexion, whereas the dynamic sensitivity increased initially but then decreased. The results indicate that recordings of the muscle afferents may provide reliable information over only a part of the physiological joint range, Despite this limitation, muscle afferent activity may be useful for motion feedback if the movement to be controlled is within a narrow joint range such as postural sway.

Position information in whole nerve cuff recordings of muscle afferents in a rabbit model of normal and paraplegic standing

Information about ankle joint position in whole nerve cuff recordings of muscle spindle afferents was examined in a rabbit model of one normal and one paraplegic subject during standing. The ankle angle of the human subjects was recorded in three experiments, and then used to simulate standing in a rabbit model. The rabbits ankle joint was moved passively by a servo controlled motor. The tibial and the common peroneal nerve activity were recorded at 3 different initial positions of the rabbits ankle joint. The results showed a change in amplitude dependent on the initial position. The tibial nerve responded in all three experiments. The peroneal nerve responded in one experiment, where the ankle angle velocity was the highest. The correlation coefficient was calculated between the nerve signal and the ankle angle. The best correlation was found when the amplitude was high and the ankle angle velocity was low. The results indicate that cuff recordings of the tibial nerve provide some information about ankle angle position when the velocity is very low. It is suggested that whole nerve cuff recordings of muscle afferents may be used as position feedback in a closed loop FES system for stabilising the ankle joint of paraplegic subjects during standing.

Effect of Intertrial Delay on Whole Nerve Cuff Recordings of Muscle Afferents in Rabbits

Objective. The effect of the stationary period on the muscle afferent responsiveness to passive stretch was studied to determine if muscle afferent activity might be suitable as feedback in motor‐neural prostheses control.

Sensory Feedback for Enhancing Upper Extremity Neuromuscular Prostheses

C5 and C6 quadriplegic individuals lack motor and sensory function in their hands. Hand grasp can be partially restored using functional neuromuscular stimulation, but controlling the synthesized grasp is hindered by the absence of tactile or proprioceptive sensation. Some of the missing information can be recovered using sensory substitution, i.e., supplemental sensory feedback. The utility of supplemental sensory feedback for control of a hand-grasp neuroprosthesis is demonstrated using shoulder position tracking tasks and an object manipulation task. The results show that providing information to the user about shoulder position (which is used to control stimulation levels) or actual grasp force improves performance. A simple, general strategy is also proposed for developing artificial sensory feedback, based on concepts of stimulus type and magnitude. The feedback modality should be chosen to match the psychophysical representation of the impaired modality, and individual feedback stimuli should evoke sensations equivalent in magnitude to those normally evoked in the impaired modality. The strategy is illustrated by using it to develop a feedback system where a variable burst duration, electrocutaneous stimulus is employed as a substitute for the normal perception of grasp force. Cross-modal matching is used to determine the appropriate stimulus transformation functions.

Natural control of wrist movements for myoelectric prostheses

Hand prosthesis function is enhanced when the user can easily perform different movement modalities. Our goal in this investigation is to enable the below-elbow prostheses user to control different wrist movements (wrist flexion/extension and forearm pronation/supination) in a natural and reliable manner. We recorded intramuscular EMG from the residual muscles (flexor carpi radialis, extensor carpi radialis, pronator teres, supinator) which are involved in these movements, and we employed combination of biofeedback training and ANN pattern recognition to obtain natural voluntary control. Finally, we evaluated the results over three different days with one-day separation between each day.