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Biomedical subjects

J R Phillips

Publications and source records attributed to J R Phillips.

At least 19 recordsLinked to original sources
PubMed1992

Responses of human mechanoreceptive afferents to embossed dot arrays scanned across fingerpad skin.

The spatial resolving capacities of the four classes of mechanoreceptive afferents innervating human fingerpad skin were investigated to determine which class sets the limit of tactile spatial resolution for scanning stimuli. The stimulus consisted of an array of embossed dots (0.7 mm diameter, 0.5 mm high) arranged in a tetragonal pattern with dot spacing decreasing linearly from 6.4 mm at one end of the array to 0.87 mm at the other. The pattern was wrapped around a drum and repeatedly scanned across the receptive field of single afferents by continuously rotating the drum. Responses to many closely spaced scans were obtained by imposing a lateral shift of the pattern between each revolution. Impulses were recorded microneurographically. Responses were plotted in raster form to produce a neural image of the pattern. Responses of rapidly and slowly adapting type I (FAI and SAI) afferents resolved dots down to a spacing of about 1.5 mm. Responses of type II (FAII and SAII) afferents resolved dots down to a spacing of about 3.5 mm. Variation in scanning speed (range, 20-90 mm/sec) and contact force (range, 0.4-1.0 N) had minimal effects on spatial resolution of all afferents. The response clusters associated with individual widely spaced dots were used to investigate receptive field structure. FAI and SAI fields (mean areas, 6.1 and 4.8 mm2, respectively) each contained several zones of maximal sensitivity. FAI fields had five to eight such zones, whereas SAI fields had three to five such zones. As dot spacing decreased, neighboring dots interacted to affect the responses associated with the individual zones within a field. Initially, one or more zones were deactivated, effectively reducing receptive field size and allowing representation of finer spatial detail than would be predicted from the overall area of the receptive field. At very close dot spacings responses were only obtained when more than one sensitive zone within a field were simultaneously activated by different dots.

Adult↗
PubMed1990

Representation of braille characters in human nerve fibres.

We have used microneurographic techniques in human subjects to record mechanoreceptive afferent responses to standard Braille characters scanned across the finger pads. Responses from all four mechanoreceptor classes (FA I, FA II, SA I and SA II) have been reconstructed to form two-dimensional Spatial Event Plots (raster plots) of the Braille alphabet. Both the SA I and FA I responses resolve the dot patterns of Braille characters with sufficient fidelity that the representations of the individual characters can be recognized visually. Responses from SA II and FA II afferents do not resolve the Braille characters. We believe that the Spatial Event Plots derived from SA I and FA I responses closely approximate the images that are transmitted within a human nerve during Braille reading.

Fingers↗
PubMed1990

Alterations in cell morphology and cytoskeletal proteins in gingival fibroblasts exposed to a Bacteroides gingivalis extract.

A soluble sonic extract (SSE) from Bacteroides gingivalis caused a dose-dependent inhibition of gingival fibroblast growth, reduced cell attachment and altered cell morphology. Most of its cytotoxic activity was destroyed by heating, indicating that the factor(s) was a protein rather than endotoxin. Cells, grown in the presence of, or on, root surfaces pretreated with 100-200 micrograms SSE/ml, partially retracted from the substratum and exhibited extensive surface blebbing and finger-like protrusions. Immunofluorescent staining showed that the morphological effects of Bacteroides gingivalis SSE are directed specifically at actin stress fibers and not microtubules of the cytoskeleton. Exposure to the SSE resulted in a dramatic relocalization of the bulk of F-actin from a fibrous form to a non-aggregated diffuse form. Disorganization of actin stress fibres occurred at concentrations of SSE that inhibited cell growth, but preceded any observable changes in cell attachment or morphology. The microtubular network remained intact, although it stained less intensely than that of controls. By contrast, Bacteroides intermedius SSE did not significantly influence growth, alter cellular morphology or affect the two cytoskeletal proteins.

Actins↗
PubMed1990

Tactile roughness: neural codes that account for psychophysical magnitude estimates.

Hypothetical neural codes underlying the sensation of tactile roughness were investigated in a combined psychophysical and neurophysiological study. The stimulus set consisted of plastic surfaces embossed with dot arrays of varying dot diameter and center-to-center spacing. Human subjects explored each surface with the pad of the index finger and reported their subjective sense of roughness magnitude. The same surfaces were scanned across the receptive fields of cutaneous mechanoreceptive afferents in monkeys while recording the evoked action potentials. Hypothetical neural codes for roughness magnitude were computed from the neural response patterns and tested for their ability to account for the psychophysical data. The psychophysical results showed that subjective roughness magnitude is an inverted U-shaped function of dot spacing that peaks near 3.0 mm spacing, and that increased dot diameter produces decreased roughness sensations at all dot spacings. Hypothetical neural codes that do not bear a consistent relationship to roughness magnitude across all of these stimulus conditions can be rejected as the code for roughness. Four types of neural codes were considered. They were based on (1) mean firing rate, (2) general variation in firing rate, (3) short-term temporal variation in firing rate, and (4) local spatial variation in firing rate. Mean firing rate failed to explain the psychophysical results: surfaces that evoked the same firing rate often evoked very different roughness judgments. In contrast, neural codes based on firing-rate variation, especially in slowly adapting afferents, account for the psychophysical results.

Action Potentials↗
PubMed1989

Behold pattern.

Explore the source record for details and available documents.

Awareness↗