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Biomedical subjects

K W Horch

Publications and source records attributed to K W Horch.

15 recordsLinked to original sources
PubMed1992

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.

Blindness↗
PubMed1992

Separation of action potentials in multiunit intrafascicular recordings.

Classification of action potentials in multiunit recordings was based on the use of various types of features to uniquely characterize action potentials from different cells. We compared classification results obtained using three types of descriptive features: digitized data points, amplitude and duration (time domain) parameters, and fast Fourier transform (FFT) coefficients. Digitized data points used as descriptive features provided good classification success and required minimal computation. Time-domain features gave comparable results but required more computation. FFT coefficients were less effective than the other features. As the signal-to-noise ratio of the recordings increased, smaller differences in feature values could be discriminated.

Action Potentials↗
PubMed1992

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.

Humans↗
PubMed1991

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

A method has been developed for the manufacture of a "three-dimensional" electrode array geometry for chronic intracortical stimulation. This silicon based array consists of a 4.2 x 4.2 x 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. 1) Thermomigration of 100 aluminum pads through an n-type silicon block. This creates trails of highly conductive p+ silicon isolated from each other by opposing pn junctions. 2) A combination of mechanical and chemical micromachining which creates individual penetrating needles of the p+ silicon trails. 3) Metal deposition to create active electrode areas and electrical contact pads. 4) Array encapsulation with polyimide. The geometrical, mechanical, and electrical properties of these arrays should make them well suited as interfaces to cortical tissue.

Animals↗
PubMed1991

Information contained in sensory nerve recordings made with intrafascicular electrodes.

Multiunit recordings were made in anesthetized cats with chronically implanted intrafascicular electrodes over a period of six months. Neural signals recorded with these electrodes consisted of activity in sensory fibers innervating a variety of cutaneous mechanoreceptors. Mechanical stimuli were used to selectively activate individual nerve fibers, and the receptive field and receptor type were identified for each unit. Over a period of six months, there was a net shift in the recorded population, but the electrodes continued to provide a representative sample of the activity in the fascicle as a whole. The total number of units from which activity could be recorded remained roughly constant with time, and individual units persisted in the recordings for up to six months. These results indicate that intrafascicular electrodes could be used to sample information carried by individual somatosensory fibers on a long term basis.

Animals↗
PubMed1989

An intrafascicular electrode for recording of action potentials in peripheral nerves.

We are developing a new type of bipolar recording electrode intended for implantation within individual fascicles of mammalian peripheral nerves. In the experiments reported here we used electrodes fabricated from 25 microns diameter Pt wire, 50 microns 90% Pt-10% Ir wire and 7 microns carbon fibers. The electrodes were implanted in the sciatic nerves of rats and in the ulnar nerves of cats. The signal-to-noise ratio of recorded activity induced by nonnoxious mechanical stimulation of the skin and joints was studied as a function of the type of electrode material used, the amount of insulation removed from the recording zone, and the longitudinal separation of the recording zones of bipolar electrode pairs. Both acute and short term (two day) chronic experiments were performed. The results indicate that a bipolar electrode made from Teflon-insulated, 25 microns diameter, 90% Pt-10% Ir wire, having a 1-2 mm long recording zone, can be used for recording of peripheral nerve activity when implanted with one wire inside the fascicle and the other lead level with the first lead, but outside the fascicle. No insulating cuff needs to be placed around the nerve trunk.

Action Potentials↗
PubMed1989

A chronic intracortical electrode array: preliminary results.

Two sets of electrode arrays made of either 25- or 50-microns-diameter Teflon-insulated platinum-iridium wire and Teflon have been developed for chronic intracortical electrical stimulation. Cortical histological studies were performed following acute and chronic implantation in cats. While some neural damage resulted from the implantations of either array configuration, a unique set of problems was associated with each diameter wire. Arrays with 50-microns electrodes and lead wires tended to maintain interelectrode spacing upon implantation, but the percutaneous leads retained residual stress which made array implantation difficult. Arrays with 25-microns electrodes and lead wires suffered from changes in interelectrode spacing upon implantation, but were much easier to manipulate during surgery. Both array configurations demonstrated some movement after implantation. It is concluded that a chronic intracortical stimulating electrode array of this geometry should have the following properties: 1) the penetrating electrodes and supporting substrate must be stiff (to maintain interelectrode spacings upon implantation), and 2) the percutaneous leads must be extremely flexible (to avoid array movement after implantation).

Animals↗
PubMed1977

A key to the classification of cutaneous mechanoreceptors.

The cutaneous mechanoreceptors of the cat can be assigned to one of 11 groups by using physiologic tests performed with hand-held stimulators. The method of classification is described, and the validity and utility of this classification scheme are discussed.

Animals↗
PubMed1976

Ascending collaterals of cutaneous neurons in the fasciculus gracilis of the cat.

Primary sensory neurons with myelinated axons in the sural nerve of the cat were found to be divisible into 3 systems on the basis of the length of their central collaterals in the dorsal columns. The short system consists of neurons that ascend only a segment or two in the fasciculus gracilis above their level of entry into the spinal cord. It is composed of all neurons with peripheral conduction velocities in the Adelta range and thus includes both D hair and nociceptive neurons. Approximately 35% of the Aalpha neurons join the intermediate system and ascend 4-12 segments before leaving the forsal columns. This system is composed of all sural type I neurons, as well as about 40% of the G2 hair, 40% of the intermediate field, and 50% of the F2 field neurons in the nerve. Those nociceptive neurons conducting at Aalpha velocities also contribute to the intermediate system. The remaining G2 hair, intermediate field, and F2 field neurons, together with almost all the sural type II, G1 hair, intermediate hair and F1 field neurons, join the long system and ascend to the nucleus gracilis. Fibers in the intermediate system showed a relatively abrupt decrease in conduction velocity usually of 50% or more (median 71%) a few millimeters rostral to their entry into the spinal cord. Members of the long system also decreased in conduction velocity at this point, but the magnitude of the changes was typically less than 50% of the peripheral velocity (median 36%). In addition, the ascending collaterals of the long system underwent a second reduction in conduction velocity near the cervical enlargement.

Afferent Pathways↗
PubMed1976

Ascending collaterals of cutaneous neurons in the fasciculus gracilis of the cat during peripheral nerve regeneration.

Dorsal column projection patterns and conduction velocities of regenerating myelinated sensory neurons were studied at intervals between 1 and 12 months after transection of the sural nerve. The neurons had significantly decreased conduction velocities, both in the fasciculus gracilis and in the periphery. Although dorsal root reflexes were temporarily abolished, there was no evidence of gross rearrangement of the neurons' ascending collaterals in the dorsal columns in response to transection of their peripheral processes or as a result of reestablishment of functional peripheral connections. These findings support the hypothesis that when a regenerating cutaneous sensory neuron reforms functional peripheral connections in tissue it originally innervated, its receptor properties are similar to those it had before the nerve was lesioned.

Afferent Pathways↗
PubMed1975

Effect of activation and adaptation on the sensitivity of slowly adapting cutaneous mechanoreceptors.

The effect of adaptation on the sensitivity of type I and type II cutaneous mechanoreceptors was evaluated with test stimuli applied before, during and after a persistent indentation (offset) of the skin. It was found that the offset initially lowered the threshold to both high (100-200 Hz) and low (1-20 Hz) frequency sinusoidal stimuli, as compared with the preoffset condition. This lowered threshold increased for both stimuli as adaptation progressed. When adaptation was nearly complete, there was an appreciable residual reduction of threshold, as compared with preoffset values, for the low frequency stimuli but not for high frequency stimuli. For a time after the offset was removed, the threshold was increased above preoffset levels for both stimuli. Suprathreshold ramp displacements superimposed on an offset caused higher maximal frequencies and a larger change in frequency than before the offset was applied. This difference often was considerable (20-40 impulses/sec) even though the discharge produced by the offset had adapted to only 2-4 impulses/sec above the preoffset level. Shortly after removal of the offset, the ramp responses typically were less than before the offset was applied. Thus, these receptors are not "reset" to the preoffset condition by adaptation nor is their sensitivity reduced. On the contrary, they respond more vigorously to superimposed stimuli except for near threshold displacements that are brief and rapid.

Adaptation, Physiological↗
PubMed1975

Awareness of knee joint angle under static conditions.

The ability of subjects to match the angle of a passively positioned knee joint by active positioning of the opposite leg is nearly constant with time from 15s to 3 min. However, their ability to match this angle from memory is equally good. Thus, knowledge of joint angle after movement has ceased does not necessarily require ongoing input from tonic peripheral receptors.

Forearm↗