Warmth-insensitive fields: a tool for the psychophysical study of innocuous and noxious thermal perception Open Access

Riley, Benjamin M. (Spring 2021)

Permanent URL: https://etd.library.emory.edu/concern/etds/dz010r21s?locale=en
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Abstract

Peripheral thermosensation and nociception are inextricably linked components of our somatosensory system. Despite over 120 years of vigorous debate on the matter, the mechanisms underpinning each term of this relationship remain nebulous. In recent years, the question at the forefront of research has been whether thermosensation is served by non-specific nociceptive afferents (i.e., C- and Aδ-fibers) or by integration of activity in many specific nociceptive and non-nociceptive fibers. Answers have naturally settled around a middle term that incorporates aspects of both ideas. Now, to determine where and how these mechanisms function, researchers require methods for isolating functional components and testing the response of the system. In the case of thermosensation and pain, this task can prove daunting. Issues of non-specific and incomplete isolation by traditional techniques are exacerbated by overlapping stimulus energies that excite both systems at once. In 1998, researchers proposed the exploitation of natural gaps in cutaneous warmth sensitivity as a research tool capable of circumventing these issues. Thermosensory properties of these warmth-insensitive fields (WIFs) suggested that within their boundaries it was possible to study perception of nociceptive heat and both innocuous and nociceptive cold in utter isolation from the innocuous warm sense. Despite this, WIFs have remained woefully understudied and underutilized in thermosensation research. This study aims to utilize quantitative sensory testing (QST) to better understand the thermosensory response properties of these fields and investigate how such gaps in perception may elucidate the relationships governing innocuous and noxious thermal sensations. Our findings that varying levels of warmth sensitivity may the perception of other aspects of thermosensation suggest that continued research in WIFs has the potential to elucidate mechanisms governing the relationship between innocuous and noxious thermal perception. Notably, we provide novel documentation of a relationship between warmth insensitivity and cold nociception that presents substantial theoretical implications for the field.

Table of Contents

Introduction. 1

Evolving theories of thermosensation and pain. 3

The WIF: discretizing innocuous and noxious thermosensation. 6

Methods 10

Participants 10

Equipment 10

WIF Identification. 10

Threshold measurements 13

Measures of Pain Intensity. 15

Measures of Pain Quality. 15

Data Analysis 16

Results 17

Discussion. 26

Factors affecting the occurrence of WIFs 26

Practical considerations for identification of WIFs 27

Trends in processing heat pain accordant with disparate warmth sensitivity. 28

Altered processing of cold pain: an unexpected feature of the WIF. 29

Conclusions 32

References 33

 

Tables and Figures

Table 1. Summary of main findings, Green and Cruz, 1998………………………………………8

Figure 1. Mapping the sensitivity of the left volar forearm……………...……………………….12

Table 2. Between-group comparisons of demography and arm measurements; bidirectional

comparisons of field parameters…………..……………………………………………..18

Figure 2. Average thresholds for detection of cold, cold pain, warming/heating, and heat pain

in WIF and Non-WIF group……………………………..………...………………….…20

Figure 3. Average intensity ratings of heat-evoked pain in the WIF and Non-WIF group………21

Figure 4. Thermal quality of heat-evoked pain in the WIF and Non-WIF group………………...22

Figure 5. Thermal quality of cold-evoked pain in the WIF and Non-WIF group………………...23

Table 3. Between-group comparisons of thermosensory response profiles………………………25

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