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F J Looft

Publications and source records attributed to F J Looft.

12 recordsLinked to original sources
PubMed1996

Response of monkey glabrous skin mechanoreceptors to random noise sequences: II. Dynamic stimulus state analysis.

The responses of monkey glabrous skin slowly adapting (SAI, Merkel cell), rapidly adapting (RA, Meissner) and Pacinian corpuscle (PC) mechanoreceptors were analyzed as a function of the instantaneous position, velocity, and acceleration of a dynamic stimulus. For these experiments, a vibrotactile punctate stimulator was driven by a non-repeating-noise sequence. The resulting data (sampled stimulus waveform, windowed impulse) were processed in several ways. Initially, input-output correlation analysis was implemented to generate spike-aligned averages of the stimulus waveform preceding and following impulse initiation. From this analysis, it was determined that dual-responding RA and PC afferents--that is, those afferents that responded to both indenting and extracting stimulus movements--universally responded in a nearly perfectly symmetrical manner to the stimulus. Subsequently, two-dimensional (position, velocity) state histograms were generated and used to assess mechanoreceptor dynamic stimulus sensitivities. From these state histograms, it was determined that the threshold for impulse initiation by SAI afferents was preferentially sensitive to the indentation position of the stimulus, with only a minor sensitivity to stimulus velocity. RA afferent thresholds were sensitive to a continuum of dynamic stimulus velocities and positions. At the extremes, RA afferent impulses could be initiated by either a highly indented, low-velocity stimulus or high-velocity stimulus with a limited indentation position. PC afferents appeared to be preferentially sensitive to a combination of stimulus velocity and acceleration, but the data-sampling interval was too coarse to adequately resolve the full range of dynamic stimulus sensitivities.

Afferent Pathways↗
PubMed1996

Response of monkey glabrous skin mechanoreceptors to random noise sequences: III. Spectral analysis.

Spectral transfer functions for monkey glabrous skin tactile mechanoreceptors were computed and compared to the results from a dynamic stimulus state analysis for the same receptors. For both sets of experiments, a vibrotactile indenting punctate stimulus driven from a non-repeating-noise (NRN) signal source was used to activate afferents. In all cases, the spectral transfer function results were similar to those inferred from dynamic stimulus state analysis. However, a comparison between the laboratory data and the results from a simple neural model showed that the interpretation of spectral transfer functions is significantly enhanced when compared to the results from an instantaneous state (position, velocity, acceleration) analysis of the stimulus at the time of impulse initiation.

Afferent Pathways↗
PubMed1994

Response of monkey glabrous skin mechanoreceptors to random-noise sequences: I. Temporal response characteristics.

The response of slowly adapting (SA, Merkel cell), rapidly adapting (RA, Meissner), and Pacinian corpuscle (PC) mechanoreceptors in monkey glabrous skin were recorded while being activated with a vibrotactile indenting stimulus. For one set of experiments, the stimulator was driven by an 800-point (400-msec) pseudorandom-noise (PRN) sequence, repeated 40 times. For a second set of experiments, a non-repeating-noise (NRN) sequence was used. SA impulse patterns generated with the PRN sequence were highly regular and similar for all afferents tested. RA and PC response patterns were more varied, but exhibited basic intraclass similarities. SA and RA PRN stimulus impulse patterns were often nearly indistinguishable at low to medium discharge rates. At higher discharge rates, RA and SA discharge patterns differed, primarily because of the unambiguous suprathreshold velocity sensitivity and shorter recovery periods of RA afferents. PC impulse patterns were substantially different from SA and RA patterns, being clearly dependent on the stimulus velocity at all stimulus intensities. Input-output correlation analysis, coupled with PRN stimulus-response analysis, provided a basis for hypothesizing the basic dynamic encoder function of each type of mechanoreceptor.

Afferent Pathways↗
PubMed1990

Linear systems analysis of cutaneous type I mechanoreceptors.

Linear system transfer functions of Type I mechanoreceptor domes in hairy skin were extracted for study. The system input, defined in units of indentation depth, was a punctate, 85 Hz bandlimited colored noise indenting stimulus. The system output was a dome's afferent AP event stream. After digitally low-pass filtering the AP event stream to prevent aliasing, transfer and coherence function estimates were generated from spectral and cross spectral estimates of the sampled input and output signals. Transfer function magnitudes (receptor sensitivity) beyond 10 Hz could be well fit by a fractional exponent (0.35 +/- 0.10) of frequency, indicating fractional order differentiation. Transfer function phases were near 120 degrees for frequencies less than 10 Hz and decreased progressively beyond 10 Hz. Coherence function estimates were low as a result of inherent nonlinearities, primarily rectification. Single dome results closely matched those reported by French and Kuster [6] for the tactile spine of the cockroach, suggesting that in terms of spectral sensitivity the receptors have similar transduction mechanisms. However, nonlinear systems modeling techniques are required for a more complete system characterization.

Action Potentials↗
PubMed1988

Swept period grating stimuli applied to cutaneous receptors.

Grating stimuli with successively larger integrate periods (also known as "swept period") are described and characterized. Since the swept period gratings are used to study the temporal frequency response functions of cutaneous receptors, a stimulator that can be used to draw these stimuli over the surface of the skin with precisely controlled motion is also described. The use of a swept period grating stimulus is illustrated for the specific case of stimulating a cat, hairy skin, slowly adapting Type I mechanoreceptor.

Animals↗
PubMed1986

Response of cat cutaneous mechanoreceptors to punctate and grating stimuli.

Cat hairy skin type I, type II, and field mechanoreceptor response characteristics were studied by drawing punctate and grating stimuli across a unit's receptive field (RF). Area RF maps were generated with scans covering approximately 1 X 1 cm using different vertical loadings, scan velocities, and scan orientations. The results from stimulating with a 1 g mass, 1 mm diam, rounded-tip punctate probe indicate that type I units display essentially invariant response topographies as a function of stimulus parameters. Type II units, presumably because of their unidirectional stretch sensitivity, showed response differences that were a function of the scan orientation. Field units, although not considered to be important for stimulus feature extraction, also displayed a directionally sensitive response profile. Changing the vertical loading or the scanning velocity of the stimulus had a minimal affect on the resulting RF profiles for any of the units studied. Grating stimuli with periods of 0.25-2.0 mm were scanned over receptors to study their grating discrimination ability. Different scan directions were used to study the directional sensitivity of a unit. Both type I and II units had optimal scan orientations for minimum grating period discrimination. For type I units, the dome orientation pattern and interdome sensitivities seemed to be a factor in determining the scan direction for minimum grating period detection. For type II units it was equivocal whether scanning parallel or orthogonal to the direction of maximum stretch sensitivity was better for grating detection. Grating response results were qualitatively similar to the results reported by others for receptors in the glabrous skin of primates. Both type I and II units could reliably discriminate gratings with periods of 0.75 mm and could marginally discriminate gratings with 0.5-mm periods. Field units were not well represented in this study, but those units that were studied were unable to unambiguously discriminate a 2.0-mm period grating, the largest one used.

Animals↗
PubMed1984

A microprocessor-based tissue displacement monitor for in vitro quantification of knee capsule deformation.

The advantages of utilizing a microprocessor design kit as a central element in custom laboratory instrumentation are demonstrated in the design of a real-time, multiple point, tissue displacement monitor. The tissue sample to be monitored is submerged in a saline bath, through which perpendicular electric fields are alternately generated. Analog displacement data are generated by differentially amplifying the voltage between each of 4 sense electrodes attached to the tissue surface, and a reference electrode, positioned on the tissue surface central to the sense electrodes. The microprocessor unit is used to control field generation, to multiplex the sensing electrode signals through the analog signal processing electronics, and after analog-to-digital conversion, to scale and interface the digital displacement data to a host processor.

Amplifiers, Electronic↗