Exploring the process of itch and its dimensionality : investigations using transcranial magnetic stimulation

Jones, Olivia Hollie

Psychology
November 2016

Thesis or dissertation


Rights
© 2016 Olivia Hollie Jones. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.
Abstract

This thesis explored three main areas of acute itch: firstly, how to reliably measure it; secondly, whether it is of a multi-dimensional nature, and lastly, which brain regions are crucial in the process. Chapter 2 reports an experiment that directly compared the re-test reliability of three commonly used measurement scales (pVAS, tVAS and gLMS). The general Labelled Magnitude Scale (gLMS) generated the least variance in itch intensity ratings between testing sessions and was therefore taken as the most reliable and administered for the following experiments. Chapter 3 and 4 explored the dimensionality of histamine and cowhage induced itch. The aims of these chapters were, (1) to explore any changes in the time-course and peak of itch intensity/unpleasantness, induced by varying stimuli doses, (2) to examine any dissociation between itch intensity and unpleasantness, which would indicate that they are dissociable dimensions. The results demonstrated that there was a significant linear trend for both intensity and unpleasantness, however there was no significant difference between the dimensions. Based on these results, it was decided that only the intensity should be measured in the following transcranial magnetic stimulation (TMS) experiment, as the unpleasantness dimension did not appear to add any additional information. Chapter 5 describes a TMS study, investigating which brain areas have a necessary function in the process of histamine and cowhage induced itch. The aim was to explore any differences in the perceived itch intensity, after brain stimulation to the somatosensory cortices (S1 and S2) and the inferor frontal gyrus (IFG), in comparison to the control area (superior parietal lobe; SPL). The results demonstrated that only TMS to S1 significantly reduced the itch intensity when administered via the histamine prick test. There was also a significant reduction of the wheal induced in the S1 and IFG condition. There was however, no significant reduction of the flare for any condition. There was also no significant difference in itch intensity or skin response, for any of the brain regions stimulated when cowhage was administered. In summary, the results indicate that S1 has a crucial role in the processing of itch intensity, and that the histamine prick test and TMS are ideal for exploring this. More investigation is necessary however, to explore the role of S2 and the IFG in itch perception.

Publisher
Department of Psychology, The University of Hull
Supervisor
Holle, Henning; Schindler, Igor
Sponsor (Organisation)
University of Hull
Qualification level
Doctoral
Qualification name
PhD
Language
English
Extent
2 MB
Identifier
hull:15694
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