Biomedical subjects

Stanley J Bolanowski

Publications and source records attributed to Stanley J Bolanowski.

22 records · Page 2Linked to original sources

PubMedDate not supplied

Vibrotactile thresholds of the Non-Pacinian I channel: I. Methodological issues.

Thresholds of the Non-Pacinian I (NP I) channel were measured using a two-interval forced-choice paradigm, a technique independent of the subject's criterion. The studies were performed using the terminal phalanx of the human middle finger with a 40-Hz vibratory stimulus. Unlike most of the previous experiments performed in our laboratory, a contactor surround was not used. This was done to enable comparison with population models of mechanoreceptive fibers in the literature. Since the Pacinian (P) channel and NP I channel have similar vibrotactile thresholds at 40?Hz, a forward-masking procedure was used to elevate the thresholds of the P channel with respect to the NP I channel. While it has been established that the Pacinian fibers are entrained at high stimulus levels, the P channel can be perceptually masked using a 250-Hz stimulus presented prior to the 40-Hz test stimulus. The masking functions were found to be approximately linear on log-log axes and the threshold shifts were found to increase as the masking-stimulus levels increased. The results are discussed in relation to previous studies that were performed at various stimulation sites by using a contactor surround or not. A companion paper presents the variation of NP I-channel thresholds, measured using the methods described herein, and addresses the effects of stimulation along the proximo-distal axis of the phalanx. The companion paper also discusses the predictions of a computational model, recently proposed, in light of the empirical results presented.

Adaptation, Physiological↗

PubMedDate not supplied

Vibrotactile thresholds of the Non-Pacinian I channel: II. Predicting the effects of contactor location on the phalanx.

The firing-rate-based population model for rapidly-adapting (RA) mechanoreceptive fibers by Güçlü and Bolanowski is extended by including temporal-response properties of RA fibers. This representation allows for the generation of action-potential (spike) times for each fiber when a sinusoidal, steady-state stimulus is applied onto the skin. Signal detection theory was used to predict human psychophysical thresholds. Specifically, the effects of sensorineural innervation pattern, stimulus-contactor location and selected decision rules on the model predictions were studied. The predicted thresholds were lowest when the decision rule was one spike and highest when many active fibers were required for detection. These predictions were empirically tested by measuring vibrotactile thresholds of the Non-Pacinian I (NP I) channel, which required the special techniques discussed in the preceding article. Although the model predicted thresholds to decrease distally due to the known innervation density which is higher distally, the thresholds of the NP I psychophysical channel were found to be approximately constant (20-25 dB re 1 microm peak amplitude) from the proximal site on the terminal phalanx to the most distal portion. Interestingly, the mechanical impedance of the skin was found not to be constant along the proximo-distal axis. This latter result implies that the space-invariant mechanical attenuation function used in the model may not be valid at every location on the fingertip. Because of this, the discrepancy between the model's predictions and the psychophysical results may be reconciled.

Action Potentials↗

PubMedDate not supplied

Ovoid geometry of the Pacinian corpuscle is not the determining factor for mechanical excitation.

Static displacements in Pacinian corpuscles (PCs) were measured using video microscopy. Mechanical stimuli of 10-40 microm steps were applied to the PC capsule surfaces using cylindrical contacts with different diameters. Displacements parallel to the stimulation axis were measured at various locations in the focal plane of the optical setup. In contrast to previous data in the literature, the displacements within the corpuscle were found to be linearly related to the indentation amplitude. Displacements decreased as a function of lamella depth, with a more negative slope close to the surface and less negative slope at deeper locations. The experimental data were compared to the predictions of a previous mechanical model, and to the results of two new models: (1) elastic semi-infinite continuum model; (2) ovoid isotropic finite-element model. Although the previous model did not specify displacement boundary conditions, it predicted the current experimental results well. On the other hand, the experimental displacements were found to be smaller than those predicted by the semi-infinite continuum and finite-element models. However, both semi-infinite continuum and finite-element models yielded close results, which show that the three-dimensional ovoid geometry of the corpuscle is not the primary factor for determining the displacements in physiological conditions. Furthermore, simulations with the finite-element model using a wide range of material properties yielded similar results. This supports the hypothesis that a homogeneous isotropic model for the PC cannot predict experimental results. The modeling analyses suggest that the experimental results are largely affected by the displacement of the incompressible interlamellar fluid and the layered structure of the corpuscle.

Animals↗

PubMedDate not supplied

Constrained optimization of Drude's equations eliminates effects of confounding molecules for the polarimetric measurement of glucose.

Common confounding factors for polarimetric concentration measurements include additional optical rotations from unknown optically active molecules, linear birefringence of the medium, and path length variability. We show that by approximating Drude's equation and taking several measurements from the same sample at different wavelengths, the error due to confounding rotations in the measurements can theoretically be canceled. The analysis is developed with regard to glucose sensing in aqueous humor. First, we show that the optical rotatory dispersions of the known molecules in bovine aqueous humor could be represented by Drude's equations. Then, the total optical rotation is approximated by a function combining Drude's equations for the major contributors in the sample, i.e., glucose, glutamine, fructose, and phenylalanine. The concentration-related unknown coefficients in the approximating function are found by constrained nonlinear optimization of the function at different wavelengths. This technique is tested on a published data set and four alterations of those data: (1) concentrations randomly varied within narrow limits, (2) similar to alteration 1 but with significantly elevated glucose concentration, (3) similar to alteration 1 but with significantly decreased glucose concentration, and (4) concentrations randomly varied within wider limits than alteration 1. The method produces very accurate glucose-concentration estimates in all of these data sets. The relative error was smaller than 1% in all except the low-glucose sample (1.4%). This method may prove useful in noninvasive glucose measurement in humans.

Algorithms↗