When we touch an object, surface loads imposed on the skin are transmitted to thousands of specialized nerve endings (mechanoreceptors) embedded within the skin. These mechanoreceptors transduce the mechanical signals imposed on them into a neural code of the incident stimuli, enabling us to feel the object. To understand the mechanisms of tactile sensation, it is critical to understand the relationship between the applied surface loads, mechanical state at the mechanoreceptor locations, and transduced neural codes. In this paper, we characterize the bulk viscoelastic properties of the primate finger pad and show its relationship to the dynamic firing rate of SA-1 mechanoreceptors. Two three-dimensional (3D) finite element viscoelastic models, a homogeneous and a multilayer model, of the primate fingertip are developed and calibrated with data from a series of force responses to micro-indentation experiments on primate finger pads. We test these models for validation by simulating indentation with a line load and comparing surface deflection with data in the literature (Srinivasan, 1989, “Surface Deflection of Primate Fingertip Under Line Load,” J. Biomech., 22(4), pp. 343–349). We show that a multilayer model with an elastic epidermis and viscoelastic core predicts both the spatial and temporal biomechanical response of the primate finger pad. Finally, to show the utility of the model, ramp and hold indentation with a flat plate is simulated. The multilayer model predicts the strain energy density at a mechanoreceptor location would decay at the same rate as the average dynamic firing rate of SA-1 mechanoreceptors in response to flat plate indentation (previously observed by Srinivasan and LaMotte, 1991 “Encoding of Shape in the Responses of Cutaneous Mechanoreceptors,” Information Processing in the Somatosensory System (Wenner-Gren International Symposium Series), O. Franzen and J. Westman, eds., Macmillan Press, London, UK), suggesting that the rate of adaptation of SA-1 mechanoreceptors is governed by the viscoelastic nature of its surrounding tissue.

References

References
1.
Phillips
,
J. R.
, and
Johnson
,
K. O.
,
1981
, “
Tactile Spatial Resolution. II. Neural Representation of Bars, Edges, and Gratings in Monkey Primary Afferents
,”
J. Neurophysiol.
,
46
(
6
), pp.
1192
1203
.
2.
Srinivasan
,
M. A.
, and
LaMotte
,
R. H.
,
1991
, “
Encoding of Shape in the Responses of Cutaneous Mechanoreceptors
,”
Information Processing in the Somatosensory System
(Wenner-Gren International Symposium Series),
O.
Franzen
, and
J.
Westman
, eds.,
Macmillan Press
,
London, UK
.
3.
Phillips
,
J. R.
, and
Johnson
,
K. O.
,
1981
, “
Tactile Spatial Resolution. III. A Continuum Mechanics Model of Skin Predicting Mechanoreceptor Responses to Bars, Edges, and Grating
,”
J. Neurophysiol.
,
46
(
6
), pp.
1204
1225
.
4.
Knibestöl
,
M.
,
1973
, “
Stimulus-Response Functions of Rapidly Adapting Mechanoreceptors in the Human Glabrous Skin Area
,”
J. Physiol.
,
232
(
3
), pp.
427
452
.10.1113/jphysiol.1973.sp010279
5.
Knibestöl
,
M.
,
1975
, “
Stimulus-Response Functions of Slowly Adapting Mechanoreceptors in the Human Glabrous Skin Area
,”
J. Physiol.
,
245
(
1
), pp.
63
80
.10.1113/jphysiol.1975.sp010835
6.
Srinivasan
,
M. A.
, and
Dandekar
,
K.
,
1996
, “
An Investigation of the Mechanics of Tactile Sense Using Two-Dimensional Models of the Primate Fingertip
,”
ASME J. Biomech. Eng.
,
118
(
1
), pp.
48
55
.10.1115/1.2795945
7.
Maeno
,
T.
, and
Kobayashi
,
K.
,
1998
, “
FE Analysis of the Dynamic Characteristics of the Human Finger Pad With Objects With/Without Surface Roughness
,”
ASME Dynamic Systems and Control Division
, DSC-64,
Anaheim, CA
, pp.
279
286
.
8.
Dandekar
,
K.
,
Raju
,
B. I.
, and
Srinivasan
,
M. A.
,
2003
, “
3-D Finite-Element Models of Human and Monkey Fingertips to Investigate the Mechanics of Tactile Sense
,”
ASME J. Biomech. Eng.
,
125
(
5
), pp.
682
691
.10.1115/1.1613673
9.
Lesniak
,
D. R.
, and
Gerling
,
G. J.
,
2009
, “
Predicting SA-I Mechanoreceptor Spike Times With a Skin-Neuron Model
,”
Math. Biosci.
,
220
(
1
), pp.
15
23
.10.1016/j.mbs.2009.03.007
10.
Gerling
,
G.
,
Rivest
,
I.
,
Lesniak
,
D.
,
Scanlon
,
J.
, and
Wan
,
L.
,
2014
, “
Validating a Population Model of Tactile Mechanotransduction of Slowly Adapting Type I Afferents at Levels of Skin Mechanics, Single-Unit Response and Psychophysics
,”
IEEE Trans. Haptics
,
7
(
2
), pp.
216
228
.10.1109/TOH.2013.36
11.
Srinivasan
,
M. A.
,
1989
, “
Surface Deflection of Primate Fingertip Under Line Load
,”
J. Biomech.
,
22
(
4
), pp.
343
349
.10.1016/0021-9290(89)90048-1
12.
Gerling
,
G. J.
,
2010
, “
SA-I Mechanoreceptor Position in Fingertip Skin May Impact Sensitivity to Edge Stimuli
,”
Appl. Bionics Biomech.
,
7
(
1
), pp.
19
29
.10.1080/11762320903069992
13.
Wagner
,
M.
,
Gerling
,
G. J.
, and
Scanlon
,
J.
,
2008
, “
Validation of a 3-D Finite Element Human Fingerpad Model Composed of Anatomically Accurate Tissue Layers
,” 2008
IEEE
Haptic Interfaces for Virtual Environment and Teleoperator Systems, Reno, NV, Mar. 13–14, pp.
101
105
.10.1109/HAPTICS.2008.4479922
14.
Serina
,
E. R.
,
Mote
,
C. D.
, and
Rempel
,
D.
,
1997
, “
Force Response of the Fingertip Pulp to Repeated Compression—Effects of Loading Rate, Loading Angle and Anthropometry
,”
J. Biomech.
,
30
(
10
), pp.
1035
1040
.10.1016/S0021-9290(97)00065-1
15.
Maeno
,
T.
,
Kobayashi
,
K.
, and
Yamazaki
,
N.
,
1998
, “
Relationship Between the Structure of Human Finger Tissue and the Location of Tactile Receptors
,”
Bull. JSME Int. J.
,
41
(
1
), pp.
94
100
.10.1299/jsmec.41.94
16.
Pawluk
,
D. T. V.
, and
Howe
,
R. D.
,
1999
, “
Dynamic Contact of the Human Fingerpad Against a Flat Surface
,”
ASME J. Biomech. Eng.
,
121
(
6
), pp.
605
611
.10.1115/1.2800860
17.
Wu
,
J. Z.
,
Welcome
,
D. E.
, and
Dong
,
R. G.
,
2006
, “
Three-Dimensional Finite Element Simulations of the Mechanical Response of the Fingertip to Static and Dynamic Compressions
,”
Comput. Methods Biomech. Biomed. Eng.
,
9
(
1
), pp.
55
63
.10.1080/10255840600603641
18.
Pelli
,
D. G.
,
1997
, “
The VideoToolbox Software for Visual Psychophysics: Transforming Numbers Into Movies
,”
Spat. Vision
,
10
(
4
), pp.
437
442
.10.1163/156856897X00366
19.
Meghani
,
S.
,
2004
, “
An Extensible Software Library for Developing Tactile Perception Experiments
,” M. Eng. and S.B. thesis, Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA.
20.
OriginLab
, “
Origin by Origin Lab Nonlinear Fitting Online Documentation
,” OriginLab Corporation, Northampton, MA,
http://www.originlab.com/doc/Origin-Help/Fitting-Nonlinear-Model
21.
Wan
,
A. W.
,
1994
, “
Biaxial Tension Test of Human Skin in vivo
,”
Biomed. Mater. Eng.
,
4
(
7
), pp.
473
486
.
22.
LaMotte
,
R. H.
, and
Srinivasan
,
M. A.
,
1991
, “
Surface Microgeometry: Tactile Perception and Neural Encoding
,”
Information Processing in the Somatosensory System
(Wenner-Gren International Symposium Series),
O.
Franzen
, and
J.
Westman
, eds.,
Macmillan Press
,
London, UK
.
23.
Tschoegl
,
N. W.
,
1989
,
The Phenomenological Theory of Linear Viscoelastic Behavior: An Introduction
,
Springer
,
New York
.
24.
Wang
,
X.
,
Schoen
,
J. A.
, and
Rentschler
,
M. E.
,
2013
, “
A Quantitative Comparison of Soft Tissue Compressive Viscoelastic Model Accuracy
,”
J. Mech. Behav. Biomed. Mater.
,
20
, pp.
126
136
.10.1016/j.jmbbm.2013.01.007
You do not currently have access to this content.