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Biomedical subjects

J M Gibson

Publications and source records attributed to J M Gibson.

At least 145 records · Page 8Linked to original sources
PubMed1983

Corticofugal influences in the rat on responses of neurons in the trigeminal nucleus interpolaris to mechanical stimulation.

We recorded effects of electrical stimulation of sensorimotor cortex on the responses of 45 neurons in the interpolar trigeminal nucleus to mechanical stimulation of vibrissae. Responses elicited by peripheral mechanical stimulation were enhanced when a neuron's receptive field (RF) included the RF of the cortical stimulating locus, and suppressed when the RFs of the cortical site and the interpolar neuron did not overlap. Several interpolaris neurons influenced by cortical stimulation were shown to project to the cerebellum.

Animals↗
PubMed1983

A new ambulatory monitoring system for tremor.

We have described a fully portable tremor recording system which allows a patient to carry out his normal day's activities with minimal hindrance. Computer analysis of the recording has enabled the extent of the tremor over prolonged periods to be presented in a format which is easily understandable and which should be useful for the objective assessment of therapy.

Ambulatory Care↗
PubMed1983

Quantitative studies of stimulus coding in first-order vibrissa afferents of rats. 1. Receptive field properties and threshold distributions.

We examined stimulus-response relationships of vibrissa-activated mechanosensory neurons of the rat's fifth (trigeminal) ganglion. Single-unit activity was recorded with tungsten microelectrodes. The vibrissae were deflected with a variety of parametrically controlled stimulus waveforms. We found that the receptive field of each vibrissa-activated neuron consisted of a single vibrissa. Few, if any, unambiguous examples of spontaneous activity were observed in these neurons. Even if true spontaneous activity was present, its observed incidence was low, as were the measured discharge rates. Thresholds of individual neurons were usually quite discrete; often a 1-2% increase in pulse magnitude (angular displacement) above a level to which the neuron did not respond caused it to discharge on every trial. The distribution of thresholds for the sample was continuous with a median of about 1 degree and a range of over three orders of magnitude. The most sensitive neurons responded to deflections of less than 0.1 degrees. Many neurons responded to a single suprathreshold pulse with more than one spike. We found no consistent relationships among the thresholds of the additional evoked discharges of an individual neuron other than that the total number of evoked spikes either increased or stayed the same, but never decreased, as stimulus magnitude increased. About one-third of the neurons examined had velocity thresholds below 3 degrees/sec. Above that value, thresholds were distributed continuously throughout a range of over three orders of magnitude. The median velocity threshold was about 100 degrees/sec. The broad and continuous distributions of both magnitude and velocity thresholds suggest that a population of vibrissa-activated neurons can code stimulus strength smoothly and continuously over a wide range, even though individual neurons may be poorly suited to do so.

Animals↗
PubMed1983

Quantitative studies of stimulus coding in first-order vibrissa afferents of rats. 2. Adaptation and coding of stimulus parameters.

Mechanosensory neurons are often classified as either rapidly adapting or slowly adapting. We examined response decay (adaptation) during constant deflection of the vibrissae with quantitative, repeatable, ad hoc measures. We found that first-order vibrissa-activated neurons of the fifth ganglion exhibit a variety of adaptation rates that appear to be distributed continuously between the rapidly and slowly adapting extremes. Also, adaptation rate is influenced markedly by stimulus magnitude. We found no evidence for a dichotomy within the more slowly adapting neurons on the basis of discharge regularity. Threshold tuning curves were used to evaluate vibration sensitivity. Both the best frequencies and 1:1 discharge thresholds for sinusoidal stimulation ranged over two orders of magnitude and were continuously distributed. First-order vibrissa-activated afferents exhibit a broad variety of response patterns to constant-velocity stimulation. The pattern of discharge varied both as a function of time during constant-velocity (ramp) deflection and as a function of stimulus velocity. Although information about the parameters of a stimulus may be conveyed by any of several features of the response pattern, it appears that few if any neurons function as "pure" encoders of any particular stimulus parameter. We examined quantitatively the relationship between discharge rate and both velocity and amplitude of vibrissa deflection with the aid of a computer-based curve-fitting procedure. We found that about half the observed rate-level functions were best described by a power function; the remainder were best fit by a logarithmic function. The parameters of the best-fitting functions varied widely and continuously, emphasizing further the diversity of coding properties of the rat's vibrissa afferents. Rate-level curves for stimulus magnitude generally exhibited saturation; some were nonmonotonic. None were described adequately by either a logarithmic function or a power function.

Adaptation, Physiological↗
PubMed1982

Stimulus-response profile analysis: a comprehensive, quantitative approach to the study of sensory coding and information processing.

In order to understand the coding and information processing capabilities of mechanosensory neurons, it is necessary to examine stimulus--response relationships under a wide variety of stimulus conditions, using a comprehensive set of quantitative analytic procedures. We employ the methodology of stimulus--response profile analysis, which is based on 4 principles: (1) the use of a broad-based battery of quantitatively controlled mechanical stimuli; (2) maintenance of comprehensive records of experiments; (3) detailed, quantitative analysis of single-unit responses; and (4) the application of these principles uniformly and consistently to all units studied. In addition to conventional graphical portrayals of single-unit activity, we employ a set of quantitative response indices, each of which represents a particular aspect of a unit's overall responsiveness. The distribution of a response index for the entire sample of neurons examined in a particular population offers insight into the manner in which a specific stimulus feature is presented within that population. The distributions of response indices obtained from different neural populations can be compared statistically in order to evaluate interpopulation differences in stimulus-response relationships. This comprehensive, quantitative approach is capable of demonstrating significant, although subtle, interpopulation differences which are not revealed by more cursory, qualitative methods.

Animals↗
PubMed1981

Trigeminocerebellar mossy fiber branching to granule cell layer patches in the rat cerebellum.

Recent micromapping studies of tactile areas in rat cerebellum have revealed a spatially precise mosaic of granule cell layer areas termed 'patches', with multiple patches on several folia resulting in multiple representations of the same body part. The research reported in the present paper tested the hypothesis that trigeminocerebellar mossy fiber branching is patch-related, so that collaterals terminate only within the boundaries of one or more of the tiny (often less than 1 sq. mm) patches having similar receptive fields. This hypothesis was supported by 3 separate series of electrophysiological experiments: (1) electrical stimulation in a patch resulted in short latency, low threshold responses confined within the boundaries of a second patch having a similar receptive field; (2) antidromic collison tests demonstrated that collaterals of axons originating in nucleus interpolaris reach pairs of patches with similar receptive fields; and (3) micromapping of the area from which a particular interpolaris neuron could be antidromically activated revealed that local terminal branching of a given mossy fiber axon appeared to be confined within the boundaries of a single patch. Together these results indicate that trigeminocerebellar mossy fiber branching is related to the fractured somatotopical organization of the granule cell layer. Possible functional implications of such mossy fiber branching are discussed.

Animals↗
PubMed1981

Principles of organization of a cerebro-cerebellar circuit. Micromapping the projections from cerebral (SI) to cerebellar (granule cell layer) tactile areas of rats.

We defined spatial patterns of organization of projections from somatosensory cerebral cortex (SI) to the somatosensory cerebellar cortex of anesthetized albino rats using microelectrode (stimulation and recording) micromapping methods and low-threshold cutaneous (tactile) stimulation. Two sampling strategies were used: (1) a single cerebral SI locus in layers V-VI was stimulated electrically, while a responding region of the cerebellar granule cell (GC) layer was systematically mapped with a recording electrode; (2) the SI stimulating electrode was used as the mapping electrode while the cerebellar GC electrode remain fixed. We found highly specific patterns of connections between somatotopically organized SI cortex and the somatotopically fractured tactile cerebellar cortex. Using threshold stimulating currents in SI, the projections from small populations of neural elements were found to be highly restricted, terminating within the confines of only those tactile cerebellar hemispheric locations having the same receptive fields (RFs). These SI-GC projections conform to the patchy mosaic pattern of organization previously shown for peripheral tactile projections. SI projections to GC patches were either contralateral or ipsilateral, depending on the laterality of the peripheral projections to that patch. Each SI focus projected to only a portion of a patch; projections from several adjacent SI loci overlapped serially within a patch. As with the peripherally evoked GC layer responses, SI-evoked GC responses were organized in a columnar fashion and were maximal at middle levels of the GC layer; SI-GC latencies were 5-8 ms. These data reveal that this tactile-related cerebro-cerebellar circuit exhibits precisely organized patterns of projection.

Animals↗
PubMed1980

Physicians and lawyers: science, art, and conflict.

The relations between physicians and lawyers have deteriorated rapidly over the past several decades, most particulary since the early 70s when the perception that a medical malpractice crisis existed in America became widespread. Some believe that the factors dividing the two professions are linked (1) to professional jealousy, (2) to sometimes conflicting economic interests, or (3) to difficulties in communication, since both professions use many of the same words, or terms of art, but with different intended meanings. While the authors agree that these factors may have aggravated the problem, they believe that the conflict's real roots are in the very different ways in which physicians and lawyers are trained and in the different epistemologies that each profession has accepted, as a result of which each reasons and solves problems in a manner that not only diverges from but sometimes contradicts the other's. The authors conclude that only as the varying epistemologies begin to converge can physicians and lawyers begin to approach problems in more similar ways, and to discover the underlying compatibility of many of their interests and goals.

Attitude of Health Personnel↗
PubMed1978

Tactile projections to granule cells in caudal vermis of the rat's cerebellum.

We discovered a small tactile area in a single a folium of the uvula of the cauday vermis of the rat's cerebellum. Gentle mechanical stimulation of relatively small cutaneous receptive fields (RFs) activated multiple units in the granule cell (GC) layer in a portion of a single folium in rats anesthetized with sodium pentobarbital. The total size of this area on each side of the midline is about 1.5 mm2, yet micromapping within this tiny region using tungsten ball microelectrodes and a high puncture sampling density (about 75 punctures/mm2) revealed a highly differentiated pattern of cutaneous projections to the GC layer. All peripheral projections are ipsilateral; the two homologous areas from each side adjoining at the midline of folium 9a. The larger projection areas from cutaneous RFs are mostly from mystacial vibrissae and upper lip, but small projection sites from the remainder of the head, neck and forelimb also are present. The pattern of projections were patch-like, forming a fractured somatotopic pattern or mosaic, with some somatotopic and some nonsomatotopic features. Each RF activated units in a vertical column in the GC layer. This area has not been described in any mammal, and its functional role can now be studied.

Afferent Pathways↗
PubMed1977

Functional development of mechanoreceptive neurons innervating the glabrous skin in postnatal kittens.

We studied single units innervating the glabrous forepaw skin of 35 domestic kittens ranging in age from 1 to 52 postnatal days. There aspects of coding were emphasized: (a) size and force thresholds of receptive fields, (b) time course of recovery between stimulus presentations, and (c) electrical conduction properties of the afferent nerve fibers. Receptive field (RF) size and force thresholds were (a) positively correlated with age for palmar but not digital RFs, and (b) were significantly larger on palm than on digits. Unit responsiveness was highly dependent on intertrial interval, complete recovery requiring at least 30 sec. Conduction velocity increased more rapidly than nerve fiber length, thus conduction time decreased with age. Refractory period decreased with age, but the conduction velocities of sequential spikes were proportional, regardless of age. These changes which we observed can more readily be ascribed to alterations of the mechanical properties of skin and conduction properties of nerve fibers than to changes in the coding mechanisms themselves.

Action Potentials↗