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. 2013 Mar;109(5):1350-9.
doi: 10.1152/jn.00395.2012. Epub 2012 Dec 12.

A Simple Model of Mechanotransduction in Primate Glabrous Skin

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Free PMC article

A Simple Model of Mechanotransduction in Primate Glabrous Skin

Yi Dong et al. J Neurophysiol. .
Free PMC article

Abstract

Tactile stimulation of the hand evokes highly precise and repeatable patterns of activity in mechanoreceptive afferents; the strength (i.e., firing rate) and timing of these responses have been shown to convey stimulus information. To achieve an understanding of the mechanisms underlying the representation of tactile stimuli in the nerve, we developed a two-stage computational model consisting of a nonlinear mechanical transduction stage followed by a generalized integrate-and-fire mechanism. The model improves upon a recently published counterpart in two important ways. First, complexity is dramatically reduced (at least one order of magnitude fewer parameters). Second, the model comprises a saturating nonlinearity and therefore can be applied to a much wider range of stimuli. We show that both the rate and timing of afferent responses are predicted with remarkable precision and that observed adaptation patterns and threshold behavior are well captured. We conclude that the responses of mechanoreceptive afferents can be understood using a very parsimonious mechanistic model, which can then be used to accurately simulate the responses of afferent populations.

Figures

Fig. 1.
Fig. 1.
Mechanotransduction model. The displacement x is the input to the transduction model. Velocity and acceleration are computed by numerical differentiation. Each of the 3 mechanical signals is split into positive and negative components that are rectified and multiplied by a separate weight ωi, and the resulting 6 signals are summed. A saturation filter is applied to the weighted sum. The output of the saturation filter, parametrized by I0, is the input current for the generalized integrate-and-fire model (MN Neuron; Mihalas and Niebur 2009).
Fig. 2.
Fig. 2.
Responses of a typical SA neuron to four diharmonic stimuli from the training set along with model predictions. A, top, displacement signal; center, observed spikes; bottom, model-generated spikes. The frequency pairs of the 4 diharmonic stimuli are (10,30), (5,50), (5,25), and (5,100) Hz, and their phase differences are 0, 180, 180, and 270°. The performance of the model, as gauged by Γn, was 1, 1, 0.92, and 1 for the 4 stimuli. B: first stimulus of A, shown at a finer scale. From top to bottom: mechanical displacement, velocity, acceleration, input current after adaption filter, observed spikes, and model-generated spikes.
Fig. 3.
Fig. 3.
Responses to a noise stimulus from the test set along with model predictions. Conventions for A and B are as in Fig. 2.
Fig. 4.
Fig. 4.
Model performance for the 22 neurons. Rate correlation coefficients (A) and Γn (B) for the test and training sets. Triangles, circles, and stars denote slowly adapting (SA), rapidly adapting (RA), and Pacinian (PC) neurons, respectively. The mean for each neuron type is indicated by open symbols of the corresponding shape.
Fig. 5.
Fig. 5.
Comparison of predictions of the present model (“new model”) with those of the model by Kim et al. (2010) (“old model”). A and B: rate correlation coefficients for the training and test sets, respectively. C and D: Γn for the training and test sets, respectively.
Fig. 6.
Fig. 6.
Fitted transduction parameters for all neurons (A–D). Closed symbols denote parameters obtained from individual neurons, and open symbols denote the means for each afferent type. In D, means are displaced vertically for clarity.
Fig. 7.
Fig. 7.
Rate intensity functions. Dots denote observed rates, solid lines, rates predicted using the full model, and dashed lines, predicted rates without saturation. A and B: SA neurons. C and D: RA neurons. E and F: PC neurons. A, C, and E: responses of representative individual neurons and the corresponding model predictions; B, D, and F: means over all neurons in each afferent category. Note the different scales of the ordinates in F.
Fig. 8.
Fig. 8.
Firing thresholds for SA (A–C), RA (D–F), and PC (G–I) fibers. Shown are absolute (A, D, and G) and entrainment (B, E, and H) thresholds for the neurons individually. In C, F, and I, the lines denote the geometric means of the absolute (bottom) and entrainment (top) thresholds. Experimental data, shown as dots, were obtained from Freeman and Johnson (1982).

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