Kenneth W. Horch

A silicon-based, three-dimensional neural interface: manufacturing processes for an intracortical electrode array

A method is described for the manufacture of a three-dimensional electrode array geometry for chronic intracortical stimulation. This silicon based array consists of a 4.2*4.2*0.12 mm thick monocrystalline substrate, from which project 100 conductive, silicon needles sharpened to facilitate cortical penetration. Each needle is electrically isolated from the other needles, and is about 0.09 mm thick at its base and 1.5 mm long. The sharpened end of each needle is coated with platinum to facilitate charge transfer into neural tissue. The following manufacturing processes were used to create this array: thermomigration of 100 aluminum pads through an n-type silicon block, creating trails of highly conductive p/sup +/ silicon isolated from each other by opposing pn junctions; a combination of mechanical and chemical micromachining which creates individual penetrating needles of the p/sup +/ silicon trails; metal deposition to create active electrode areas and electrical contact pads; and array encapsulation with polyimide.<<ETX>>

Direct neural sensory feedback and control of a prosthetic arm

Evidence 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 amputees 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 amputees 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.

Apparatus for automated tactile testing

An automatic apparatus for testing tactile responses of a patient is disclosed. The embodiments of the invention variously include components for: applying a nonambient temperature to the patients skin to test the patients response to thermal stimuli; pricking the patients skin to test the patients response to pain; indenting the patients skin to test the patients response to touch; vibrating the patients skin to test the patients response to vibration; and for making two spaced apart contacts with the patients skin to test the patients two point discrimination response. A general purpose computer and dedicated control circuits function to control the operation of the system and record the responses of the patient. The embodiments of the present invention are able to repeatedly reproduce each test so that the tests carried out are reproducible and accomplished in a minimum of time.

Mobility performance with a pixelized vision system

A visual prosthesis, based on electrical stimulation of the visual cortex, has been suggested as a means for partially restoring functional vision in the blind. The prosthesis would create a pixelized visual sense consisting of punctate spots of light (phosphenes). The present study investigated the feasibility of achieving visually-guided mobility with such a visual sense. Psychophysical experiments were conducted on normally sighted human subjects, who were required to walk through a maze which included a series of obstacles, while their visual input was restricted to information from a pixelized vision simulator. Walking speed and number of body contacts with obstacles and walls were measured as a function of pixel number, pixel spacing, object minification, and field of view. The results indicate that a 25 x 25 array of pixels distributed within the foveal visual area could provide useful visually guided mobility in environments not requiring a high degree of pattern recognition.

Selective stimulation of peripheral nerve fibers using dual intrafascicular electrodes

The authors have studied activation of nerve 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.<<ETX>>

Simulation of a phosphene-based visual field: Visual acuity in a pixelized vision system

A visual prosthesis for the blind using electrical stimulation of the visual cortex will require the development of an array of electrodes. Passage of current through these electrodes is expected to create a visual image made up of a matrix of discrete phosphenes. The quality of the visual sense thus provided will be a function of many parameters, particularly the number of electrodes and their spacing. We are conducting a series of psychophysical experiments with a portable “phosphene” simulator to obtain estimates of suitable values for electrode number and spacing. The simulator consists of a small video camera and monitor worn by a normally sighted human subject. To simulate a discrete phosphene field, the monitor is masked by an opaque perforated film. The visual angle subtended by images from the masked monitor is 1.7° or less, depending on the mask, and falls within the fovea of the subject. In the study presented here, we measured visual acuity as a function of the number of pixels and their spacing in the mask. Visual acuity was inversely proportional to pixel density, and trained subjects could achieve about 20/26 visual acuity with a 1024 pixel image. We conclude that 625 electrodes implanted in a 1 cm by 1 cm area near the foveal representation of the visual cortex should produce a phosphene image with a visual acuity of approximately 20/30. Such an acuity could provide useful restoration of functional vision for the profoundly blind.

Chronically implanted intrafascicular recording electrodes

A newly designed intrafascicular electrode for chronic neural recording was studied by implanting 12 electrodes in the radial nerves of 6 cats for 6 months. Action potentials were monitored at specified intervals throughout the experiment. The number and size of the signals recorded suggest that this type of electrode provides information that is appropriate for feedback control in functional electrical stimulation (FES) systems. Histology of the nerve revealed that the implants are biocompatible and that little damage is caused by the presence of the electrode.

Reading speed with a pixelized vision system

A visual prosthesis based on electrical stimulation of the visual cortex with an array of penetrating electrodes is expected to produce pixelized visual images consisting of punctate spots of light (phosphenes). We measured reading speed in subjects viewing text with optically simulated phosphene fields in order to obtain estimates of the following design parameters for such an electrode array: pixel number, pixel spacing, and visual-field size. Comparisons were made between scanning the text with eye movements and scanning the text with head movements. The results indicate that a 25 x 25 array of pixels representing four letters of text projected on a foveal visual field of 1.7 degrees is sufficient to provide reading rates near 170 words/min with scrolled text and near 100 words/min with fixed text.

Neuroprosthetics theory and practice

Neuroanatomy and neurophysiology extracellular stimulation and recording - theory and models immunology materials for nerve stimulation and recording peripheral nerve and muscle - stimulation and recording electrodes and techniques CNS stimulation and recording electrodes and techniques existing FES systems and signal processing future FES systems/devices/brain-computer interfaces experimentation and device approval.

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

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.