Direct neural sensory feedback and control of a prosthetic arm

Journal ArticleEvidence indicates that user acceptance of modern artificial limbs by amputees would be significantly enhanced by a system that provides appropriate, graded, distally referred sensations of touch and joint movement, and that the functionality of limb prostheses would be improved by a more natural control mechanism. We have recently demonstrated that it is possible to implant electrodes within individual fascicles of peripheral nerve stumps in amputees, that stimulation through these electrodes can produce graded, discrete sensations of touch or movement referred to the amputee's phantom hand, and that recordings of motor neuron activity associated with attempted movements of the phantom limb through these electrodes can be used as graded control signals. We report here that this approach allows amputees to both judge and set grip force and joint position in an artificial arm, in the absence of visual input, thus providing a substrate for better integration of the artificial limb into the amputee's body image. We believe this to be the first demonstration of direct neural feedback from and direct neural control of an artificial arm in amputees

Information extraction from peripheral nerves

Journal ArticleThis work is directed toward providing better rehabilitation for people suffering from somatosensory loss and paralysis due to spinal cord injury, head trauma, or stroke. The goal of this project is to demonstrate that information suitable for controlling prosthetic devices, modulating functional electrical stimulation of muscle, and providing a sense of touch and position from areas of the body suffering sensory loss can be extracted, on-line and in real time, from recordings of sensory activity in peripheral nerves

Tracking changes in action potential shapes in chronic multi-unit intrafascicular recordings using neural network pattern recognition techniques

Journal ArticleA novel scheme is proposed to train an Artificial Neural Network (A") classifier, on a repeated basis, in order to track temporal changes in the shapes of the action potentials recorded through chronically implanted intrafascicular electrodes. This scheme uses classification results of the ANN Classifier on the most recent neural recordings to label the new action potentials. The ANN classifier is retrained using the new samples so that it recognizes any changes in the shapes of the action potentials. The procedure is repeated continuously using the most recently trained ANN classifier. This scheme was tested on different simulated situations that may arise in a two unit neural recording. The results indicate that proposed method allows us to track the changes in the shapes of the action potentials in most plausible scenarios that might arise in chronic intrafascicular recordings

Selective stimulation of peripheral nerve fibers using dual intrafascicular electrodes

Journal ArticleWe have studied activation of newe fibers by pairs of Pt-Ir wire electrodes implanted within single fascicles of the nerve innervating the gastrocnemius muscle in cats. The purpose of this study was to determine if these intrafascicular electrodes can activate nerve fibers in different fascicles independently of each other and if they can also be used to activate separate subsets of axonal populations within a single fascicle. The average overlap of activated nerve fiber populations was 5.5% between fascicles and 27% within a fascicle, indicating that such selective activation is possible with these electrodes

Neural signal for skin indentation depth. II. Steady indentations

Journal ArticleThe glabrous skin of the monkey's hand was stimulated with a waveform that indented the skin at a rate of 0.4 mm/set, held the skin steadily or nearly steadily indented for 12 set or longer, and then retracted back to the starting position. Recordings were made of activity in single afferent fibers in response to these stimuli. The average discharge frequency of 21 slowly adapting mechanoreceptors declined 38% during the first 12 set of a steady indentation when the amplitude of the displacement was 0.65 mm and 36% when the displacement was 1.3 mm. When the plateau was not steady but the indentation depth gradually decreased by 15% during the 12-set plateau period, the average decline was 47% for the 0.65-mm indentation and 46% for the 1.3-mm stimulus. When the indentation depth gradually increased by 15% during the 12-set plateau, the discharge declined an average of 26% during the 0.65-mm indentation and 22% during the 1.3-mm displacement. To determine the effect of receptor adaptation on the perception of skin indentation depth, 13 human subjects had the skin of their fingertips indented 1 mm with similar trapezoidal waveform and were asked whether the indentation depth increased or decreased during the plateau portion of the stimulus. Ten of the 13 subjects thought that the indentation depth was increasing when the plateau was steady. The method of limits was then used to determine how much the stimulus had to change for the subject to feel the depth during the plateau as unchanging; i.e., a "perceptual zero." The average perceptual zero for the entire group occurred when the stimulator steadily retracted by 14% during the plateau. The subject whose indentation depth sensation adapted the most felt the plataeu to be steady when the stimulator gradually advanced by 15% during the plateau. A different group of 10 subjects traced the perceived depth of steady fingertip indentations which were 1 and 2 mm deep while the stimuli were actually in progress, and more than half traced a sensation of gradually increasing depth. The subject in this group whose depth sensation adapted the most showed a decline of 13% during a steady plateau 18 set long, as compared with the average discharge of our sample of slowly adapting monkey mechanoreceptors, which declined 45% during a comparable stimulus. Tracings were also made by these subjects of waveforms that remained steady for 2 to 4 set, partially retracted by 5 to 30%, and then reindented to the same depth. When the partial retractions were slow, the subjects thought the indentation depth increased with each repetition of the stimulus although the stimulator actually reindented to the same depth each time. The fact that human subjects tend to feel the depth of a steady indentation as increasing at a time when the discharge of their glabrous skin mechanoreceptor is declining could be explained if the adapting discharge were to be integrated (in the mathametical sense) by the central neural circuitry responsible for judgments of skin indentation depth. Such an integration process could also account for the increase in perceived depth during reindentation since present evidence indicates that receptor discharge declines rather than increases during repeated reindentations to the same depth

Closed loop control of ankle position using muscle afferent feedback with functional neuromuscular stimulation

Journal ArticleThis paper describes a closed-loop functional neuromuscular stimulation system that uses afferent neural activity from muscle spindle fibers as feedback for controlling position of the ankle joint. Ankle extension against a load was effected by neural stimulation through a dual channel intrafascicular electrode of a fascicle of the tibial nerve that innervated the gastrocnemius muscle. Ankle joint angle was estimated from recordings of tibialis anterior and lateral gastrocnemius spindle fiber activity made with dual channel intrafascicular electrodes. Experiments were conducted in neurally intact anesthetized cats and in unanesthetized decerebrate cats to demonstrate the feasibility of this system. The system was able to reach and maintain a fixed target ankle position in the presence of a varying external moment ranging in magnitude between 7.3 and 22 N-cm opposing the action of the ankle extensor, as well as track a sinusoidal target ankle position up to a frequency of 1 Hz in the presence of a constant magnitude 22- or 37-N-cm external moment

Classification of action potentials in multi unit intrafascicular recordings using neural network pattern recognition techniques

Journal ArticleNeural network pattern-recognition techniques were applied to the problem of identifying the sources of action potentials in multi-unit neural recordings made from intrafascicular electrodes implanted in cats. The network was a three-layer connectionist machine that used digitized action potentials as input. On average, the network was able to reliably separate 6 or 7 units per recording. As the number of units present in the recording increased beyond this limit, the number separable by the network remained roughly constant. The results demonstrate the utility of neural networks for classifying neural activity in multi-unit recordings

Control of ankle position using neural feedback

Journal ArticleThis paper describes a closed loop control system that uses afferent neural activity from muscle spindle fibers as feedback for controlling ankle position. The gastrocnemius muscle was stimulated through a dual channel intrafascicular electrode implanted in a fascicle of the tibial nerve. Dual channel intrafascicular electrodes were also used to record spindle fiber activity from the tibialis anterior and the lateral gastrocnemius muscles to estimate ankle joint angle. Experiments were conducted in neurally intact anesthetized cats and in unanesthetized decerebrate cats to demonstrate the feasibility of this control scheme

Simulation of a phosphene field based visual prosthesis

Journal ArticleA visual prosthesis for the blind based upon electrical stimulation of the visual cortex requires the development of an array of electrodes. To establish design specifications for such an electrode array, we have conducted psychophysical experiments with normally sighted subjects wearing a portable 'phosphene' simulator. The simulator consists of a small video camera, a monitor masked by an opaque perforated film, and optical lenses. The visual angle subtended by the masked monitor is 1.7" or less. We measured visual acuity and reading rate as a function of the number of pixels and their spacing. Our results indicate that a phosphene image produced by 600 electrodes implanted in a 1 cmz area near the foveal projection on the visual cortex should provide a limited but useful visual sense for the profoundly blind

Neural signal for skin indentation depth. I. Changing indentations

Journal ArticlePsychophysical tests on human subjects showed that judgments of skin indentation depth made when the fingertip was indented at rates from 0.2 to 16 mm/set were quite insensitive to changes in indentation velocity. Similar results were obtained on the forearm at indentation velocities of 0.4 to 16 mm/set. Recordings were made from mechanoreceptors in the monkey's hand that were able to respond over the same range of velocities and at comparable depths to determine how skin indentation depth might be signaled (coded) at the receptor level and to examine the rate sensitivity of the possible depth codes. It was found that most of the receptors with foci under the stimulator were recruited relatively early during an indentation, especially at velocities of 1.6 mm/set and higher, making it improbable that the full range of indentation depths is signaled by the "subsurface" recruitment of different receptors at different indentation depths. A subsurface recruitment code involving subcutaneous receptors is not likely since subjects could feel virtually none of the stimuli after skin anesthesia. Progressive recruitment with depth of receptors whose foci lie further and further away from the stimulator ("lateral" recruitment) was considered an unlikely depth code because changing the area of the stimulator had little effect on its perceived depth. Also, it was shown that subjects could sense the curvature of the identation (the profile of the depth at right angles to the skin surface), which requires information about the depth of individual patches of skin beneath the stimulator. There is no obvious way that a lateral recruitment code can provide this information. Thus it is probable that the discharge rate of some or all of the receptors excited by the indentation is involved in indicating its depth. Both impulse frequency and receptor recruitment at any given depth increased as the velocity of the identation increased. The demonstrated reliability of information about skin indentation depth in humans indicates that the central neural circuitry responsible for judgments of skin indentation depth is able to compensate for the rate-sensitive receptor signals