SENSORY PROCESSING IN BODY-FOCUSED REPETITIVE BEHAVIORS A Dissertation by DAVID CHRISTIAN HOUGHTON Submitted to the Office of Graduate and Professional Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Chair of Committee, Steve Balsis Committee Members, Douglas Woods Sherecce Fields Jessica Bernard Michael Smotherman Head of Department, Heather Lench August 2018 Major Subject: Clinical Psychology Copyright 2018 David Christian Houghton ABSTRACT Body-focused repetitive behaviors (BFRBs) such as hair pulling and skin picking are common practices that are part of ordinary grooming, but can proliferate excessively into maladaptive habits. Despite their negative consequences, affected individuals often experience great difficulty in stopping pulling/picking and report strong urges and hedonic reward associated with symptoms. Unfortunately, the psychobiological mechanisms underlying sensory features of BFRBs have been insufficiently studied. The current study aimed to explore potential sensory processing abnormalities in adults with Trichotillomania and Excoriation Disorder using several self-reported instruments and a vibrotactile behavioral battery. A total of 46 adults with either Trichotillomania or Excoriation Disorder were recruited, along with an age-matched sample of 46 healthy control participants. Participants completed clinician-rated interviews regarding their symptom severity and self-report instruments regarding interoceptive awareness and sensory gating. The vibrotactile battery consisted of several tests that assessed reaction time, sensorimotor integration, detection threshold, feed-forward inhibition, lateral inhibition, temporal processing, and duration discrimination. Persons with BFRBs reported increased interoceptive awareness, a greater propensity to worry about their body states, and less trust in their own body. In addition, the BFRB group reported greater perceptual inundation, sensory distractability, over- inclusion, and a propensity to experience sensory abnormalities while fatigued or distressed. Persons with BFRBs did not display behavioral deficits in sensorimotor ii integration, quickly adapting lateral inhibition, temporal processing, or duration discrimination. However, the BFRB group had lower tactile thresholds and deficient feed-forward inhibition. Deficient feed-forward inhibition was correlated with skin picking severity. These findings indicate that increased sensitivity to sensory stimuli and an inability to filter out excess sensory input is associated with a propensity to engage in BFRBs, perhaps as a method of distracting oneself from an aversive perceptual state. iii DEDICATION For my wife, Amanda, for her unwavering support and encouragement. Also, for Dr. Carol Yoder and Dr. Carolyn Becker, who believed in me when no one else did. iv ACKNOWLEDGEMENTS Over the past nine years I have received support and encouragement from a great number of individuals. Among those I would like to thank Alan Peterson, Antoinette Brundige, Trisha Benson, Cindy Lancaster, Craig Bryan, Ann Rost, Brandon Sanford, David Lutz, Doug Snyder, Brie van Widenfelt, Rob Heffer, Chris Bauer, Jennifer Alexander, Christine Conelea, Mike Himle, Flint Espil, and Matthew Capriotti. I would also like to thank my dissertation committee of Jessica Bernard, Sherecce Fields, and Mike Smotherman for their support over the past two years from this project’s inception until completion. In addition, I would like to thank Steve Balsis for his encouragement and invaluable mentorship during the course of my graduate study. Finally, I owe Doug Woods an immense debt for his support and mentorship throughout my doctoral work and over the course of many projects. During the design of this research, Mark Tommerdahl was an enormously helpful resource and played a large role in the protocol development. Suzanne Mouton-Odum and Tyson Reuter were very kind to lend their support to my data collection efforts. Shoaleh Motamedi devoted countless hours to checking and entering data on the project. Thanks also go to my friends and colleagues and the department faculty and staff for making my time at Texas A&M University a great experience. I would like to thank the participants of this study for their time and contribution to science. Finally, thanks to my mother, father, brother, and sister for their encouragement. v CONTRIBUTORS AND FUNDING SOURCES This work was supported by a dissertation committee consisting of Professor Steve Balsis and Professors Sherecce Fields and Jessica Bernard of the Department of Psychological and Brain Sciences, Professor Douglas Woods of the Department of Psychology at Marquette University, and Professor Michael Smotherman of the Department of Biology and Institute of Neuroscience. The protocol for the vibrotactile battery discussed in CHAPTER II was developed in concert with Professor Mark Tommerdahl from the Department of Bioengineering at the University of North Carolina, Chappell Hill. Graduate study was supported in part by a fellowship from Texas A&M University and a grant from the National Institutes of Mental Health to Douglas Woods. vi TABLE OF CONTENTS ABSTRACT ................................................................................................................... ii DEDICATION ............................................................................................................... iv ACKNOWLEDGEMENTS ........................................................................................... v CONTRIBUTORS AND FUNDING SOURCES ......................................................... vi LIST OF FIGURES ....................................................................................................... ix LIST OF TABLES ......................................................................................................... x CHAPTER I INTRODUCTION AND LITERATURE REVIEW ................................ 1 1.1 Problem Statement .............................................................................................. 1 1.2 Habits: Friend and Foe ........................................................................................ 2 1.3 How Habits Develop ........................................................................................... 10 1.4 Neurobiology of Pathological Habit Disorders ................................................... 14 1.5 Evidence for Increased Habit Formation in BFRBs ........................................... 16 1.6 Methods of Treating BFRBs ............................................................................... 20 1.7 Sensory Features of BFRBs ................................................................................ 28 1.7.1 Sensory Antecedents ................................................................................... 28 1.7.2 Sensory Consequences ................................................................................ 29 1.8 Sensory Processing Deficits in OC-Spectrum Disorders .................................... 30 1.9 Possible Mechanisms of Sensory Phenomena in BFRBs ................................... 34 1.10 Cortical Sensory Processing ............................................................................. 35 1.11 Altered Sensory Processing in OC-Spectrum Disorders .................................. 39 1.12 Current Hypotheses ........................................................................................... 42 CHAPTER II METHOD ................................................................................................ 45 2.1 Participants .......................................................................................................... 45 2.2 Measures ............................................................................................................. 52 2.3 Procedure ............................................................................................................ 56 2.4 Analyses .............................................................................................................. 60 CHAPTER III RESULTS .............................................................................................. 62 3.1 Tests of Potential Covariates .............................................................................. 62 3.2 Behavioral Data .................................................................................................. 62 3.3 Reaction Time and Basic Sensorimotor Function .............................................. 64 3.4 Detection Threshold ............................................................................................ 65 3.5 Amplitude Discrimination .................................................................................. 67 3.6 Frequency Discrimination ................................................................................... 68 3.7 Duration Discrimination ..................................................................................... 70 3.8 Association Between Performance and Self-Report ........................................... 71 vii CHAPTER IV DISCUSSION ....................................................................................... 74 4.1 Review of Findings ............................................................................................. 74 4.2 The Potential Role of Sensation in BFRB Psychopathology .............................. 79 4.3 Limitations and Future Directions .....................................................................