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Biomedical subjects

K W Horch

Publications and source records attributed to K W Horch.

At least 37 records · Page 2Linked to original sources
PubMed1984

Rapid displacements of the skin lack clear positional information.

Rapid skin indentations can produce strong tap-like sensations that contain little information about skin indentation depth. Although slower stimuli produce weaker sensations, subjects can more accurately identify how the position of the skin surface changes with respect to the deeper tissues. This dissociation between intensity and depth information suggests that intensity and depth are served by different neural circuits.

Humans↗
PubMed1984

The neural signal for the intensity of a tactile stimulus.

The effect of indenting the skin at different rates on the perceived intensity of the stimulus was studied by indenting the skin of the fingertip with two triangular waveforms, given as a pair. The subjects were asked to judge which member of the pair was more intense. Perceived intensity was found to increase both with the depth and the speed of the indentation. In contrast, changes in the rate of skin indentation had little influence on perceived skin indentation depth. This suggests that intensity and depth are different attributes of tactile sensibility. Since the skin is viscous, a rapid indentation is more forceful than a slow indentation of the same depth, raising the possibility that perceived intensity is related to stimulus force. Even though intensity judgments were more closely correlated with the force of a stimulus than with the indentation it produced, a rapidly increasing force was felt as more intense than one that increased more slowly but attained the same final magnitude. When mechanoreceptors in the palmar aspect of the monkey's hand were excited with triangular stimuli like those used in the psychophysical studies, their discharge frequency increased with the rate of skin indentation. However, the receptors were distinctly more rate sensitive than the human judgments of stimulus intensity, suggesting that impulse summation in the central nervous system summates (integrates in the mathematical sense) the receptor input so as to enhance, relatively, the perceived intensity of the slower stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1983

A quantitative evaluation of suture and tubulization nerve repair techniques.

The radial and sural nerves in cats were transected and either left unrepaired, repaired with 11-0 epineurial sutures, sutured and treated with topical application of Kenalog, or tubulated with hypoantigenic collagen. One year later the nerves were examined electrophysiologically, using single unit recording techniques, and histologically, by light microscopy. The results indicate that regeneration through the neuroma was comparable in all four groups, but that reinnervation of sensory structures in the skin was most successful in the tubulated nerves.

Animals↗
PubMed1983

The neural signal for skin indentation depth. II. Steady indentations.

The glabrous skin of the monkey's hand was stimulated with a waveform that indented the skin at a rate of 0.4 mm/sec, held the skin steadily or nearly steadily indented for 12 sec 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 sec 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-sec 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-sec 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."(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1983

Boring's formulation: a scheme for identifying functional neuron groups in a sensory system.

In 1935 Edwin Boring proposed that each attribute of sensation reflects the activity of a different neural circuit. If this idea is valid, it could facilitate both psychophysical and neurophysiological research on sensory systems. We think it likely that Boring's formulation is correct for three reasons: 1) Different sensory attributes reflect conscious information about different parameters of a stimulus. To be measured by any device, each of these parameters must be individually computed. Different neural circuits would appear to be necessary for the nervous system to carry out these different computations. 2) Perceived information about different sensory attributes can be made to diverge by appropriate manipulations of the stimuli. If there is a rigorous relationship between conscious sensory experience and neural activity, such a divergence implies that different sensory attributes are served by different neural circuits. 3) Accurate information about a sensory attribute requires that a human observer's attention be focused on that attribute. Changes in direction of attention are thought to involve a process of switching from one neural circuit to another, and provide another way to cause perceived information about different sensory attributes to diverge.

Fingers↗
PubMed1983

The neural signal for skin indentation depth. I. Changing indentations.

Psychophysical 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/sec were quite insensitive to changes in indentation velocity. Similar results were obtained on the forearm at indentation velocities of 0.4 to 16 mm/sec. 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/sec 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 indentation (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 indentation 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.

Adult↗
PubMed1981

On the number and nature of regenerating myelinated axons after lesions of cutaneous nerves in the cat.

1. Electrophysiological and anatomical techniques were used to investigate normal and regenerating sural and posterior femoral cutaneous nerve fibres in the cat. 2. One and a half years after transection of these nerves it was found that the regenerating neurones supported multiple sprouts in the distal stump of the nerve. The branching occurred at or beyond the level of the neuroma and some of the branched fibres innervated split receptive fields on the skin. 3. Counts of the number of axons in the proximal stumps of transected nerves showed that the whole original population of myelinated fibres persisted for at least 18 months. About 75% of these fibres successfully crossed the unrepaired transection site and regenerated into the distal stump of the nerve to re-form functional connexions in the skin. 4. After nerve crush all the myelinated axons regenerated. None showed signs of abnormal branching. 5. After crush the conduction velocities of the regenerated axons in the distal stump of the nerve reached nearly normal values by 6 months. After nerve transection the distal conduction velocities were reduced to 50% of normal even 18 months after the injury. 6. The implications of these findings for the recovery of function after nerve injury in man are discussed.

Action Potentials↗
PubMed1981

Changes in primary afferent depolarization of sensory neurones during peripheral nerve regeneration in the cat.

1. Micro-electrode recordings were made from normal and regenerating sural nerve fibres in cats. Increases in the excitability of the central terminals of these fibres after conditioning stimulation of other sural nerve fibres were taken as evidence for primary afferent depolarization. 2. At all recovery times studied the excitability changes seen were significantly less than those seen in control animals. Two factors contributed to the changes in primary afferent depolarization. First, the proportion of fibres that showed no evidence of primary afferent depolarization increased significantly. This proportion became smaller as recovery progressed. Secondly, where primary afferent depolarization was present, the magnitudes of the effects were slightly but significantly decreased compared with control values. 3. Excitability changes of the central terminals of sural nerve fibres were also measured after conditioning stimulation of the ipsilateral, unlesioned accessory sural nerve. One month after sural nerve transection there was a significant increase in the proportion of fibres showing no evidence of excitability changes following accessory sural nerve conditioning stimulation compared with control animals. Thus, the loss of primary afferent depolarization of regenerating sural nerve fibres was neither simply a consequence of desynchronization of the volley of impulses entering the spinal cord after conditioning stimulation of other regenerating sural fibres, nor due to fewer fibres being activated during conditioning stimulation of the lesioned nerves. 4. A possible explanation of these results is that after peripheral nerve crush or transection the central terminals of the damaged fibres retract or atrophy. Then as regeneration of the nerve proceeds, the central terminals of the fibres re-form.

Action Potentials↗
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↗
PubMed1974

Patterning in the regeneration of type I cutaneous receptors.

1. Type I sensory fibres in cat hairy skin innervate structures characterized by twenty to fifty specialized epithelial (Merkel) cells aggregated in a small dome-shaped elevation. Only one fibre enters each dome and it branches repeatedly to supply at least one terminal to each Merkel cell. After the nerve is cut, the Merkel cells and the dome ultimately disappear.2. The distribution of domes on the posterior thigh was mapped before interruption of the femoral cutaneous nerve and after its regeneration. Regeneration after nerve crush was apparently complete, producing a coincidence pattern similar to those seen in control studies where the nerve was not damaged. After cutting the nerve fewer domes returned, but coincidence of regenerated femoral cutaneous domes with old sites generally was significantly greater than would be expected by chance alone. Non-femoral cutaneous fibres sprouting into the denervated femoral cutaneous field tended to form domes at old sites. Domes were also reformed on scars where domes had been excised.3. Domes appearing at new locations and on excision scars were often small and close together (clustered). Individual domes in a cluster could be innervated by different Type I fibres.4. Type I fibres are directed by some mechanism to sites formerly occupied by domes and to sites where domes are being induced.

Animals↗