AN ABSTRACT OF THE THESIS OF Julie L. Colvin for the degree of Master of Science in Food Science and Technology presented on June 8, 2018. Title: Differences in Taste Responses between Tongue Regions Abstract approved: _____________________________________________________________________ Juyun Lim Due to a combination of misinterpretation and misleading illustration, the premise of a “tongue map”, which indicated that sweetness could only be detected at the front of the tongue and bitterness could only be detected on the back, became wide spread. In fact, all taste qualities can be detected on the front, back and sides of the tongue. Studies on regional differences within the oral cavity have typically reported differences in taste response depended on taste quality. Most of these studies have had subjects keep their tongue still or mouth open while evaluating samples to prevent the spread of stimuli to other regions of the oral cavity. However, tongue and mouth movements are naturally paired with taste perception in normal eating situations. This intraoral movement can cause stimuli to spread throughout the mouth and may have additional effects on taste perception. Therefore, studying the effects of intraoral tongue and mouth movements may be important to understanding taste perception mechanisms. Notably, some reports have not specified the tasting mode used in their study. In addition, it has been suggested that maltooligosaccharides (MOS) may be detected independently from the classic sweetness receptor, but it is unknown whether regional responsiveness differs between sucrose and MOS. The current study was designed to investigate 1) the effects of taste quality on regional differences in responsiveness between the front and back of the tongue, and 2) the effects of “passive” and “active” tasting modes on relative regional differences in taste responsiveness. Along with the two carbohydrates tested (i.e. sucrose and MOS), quinine and MPG were also included to represent bitter and umami taste qualities, respectively. In the passive tasting condition, the front of the tongue was found to be more responsive to both carbohydrates, but no regional differences were seen for quinine or MPG. In the active tasting condition, the back of the tongue was more responsive to quinine and MPG, but no differences were found for either carbohydrate. These findings indicate that there are regional differences in taste responsiveness between the front and back of the tongue, and that they are dependent on taste quality and modulated by tasting mode. Further, the effects of tasting mode were taste quality dependent only on the back of the tongue. This indicates that interactions between taste and intraoral movements may be different between tongue regions. ©Copyright by Julie L. Colvin June 8, 2018 All Rights Reserved Differences in Taste Responses between Tongue Regions by Julie L. Colvin A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Presented June 8, 2018 Commencement June 2018 Master of Science thesis of Julie L. Colvin presented on June 8, 2018. APPROVED: _____________________________________________________________________ Major Professor, representing Food Science and Technology _____________________________________________________________________ Head of the Department of Food Science and Technology _____________________________________________________________________ Dean of the Graduate School I understand that my thesis will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my thesis to any reader upon request. _____________________________________________________________________ Julie L. Colvin, Author ACKNOWLEDGEMENTS First, I would like to express my sincere appreciation to my major advisor, Dr. Juyun Lim, for allowing me the opportunity to join this lab. Her work ethic and passion for science inspired me to pursue research, and her expertise and mentorship have helped me grow as a researcher, writer, and scientist. I would also like to thank my committee members, Dr. Michael Penner, Dr. Elizabeth Tomasino and Dr. James Hermes, for their feedback on the present work and commitment of time as part of my defense committee. Further, I would like to thank my current and former lab mates, Alex Pullicin, Tyler Flaherty, Trina Lapis, Tyler Linscott, Amy Balto, Rachel Silver, and Erin Schenk, for helping me grow as a researcher and for making my experience in graduate school more fun. To the students, staff, and faculty of the Food Science and Technology Department, thank you for your help, guidance and support throughout my time here at OSU. I would also like to acknowledge Sue Queisser, Aimee Hasenbeck, and the others who I worked with in the consumer lab, thank you for your support and insights into food science and other topics. I would also like to thank my friends, those at OSU and not, who have been there for me when it was time to step out of the lab, library, and classroom for a while. Finally, I would like to dedicate this work to my family. Thank you for your unwavering support during my time in this program. CONTRIBUTION OF AUTHORS Julie Colvin wrote Chapters 1 and 3. Julie Colvin performed the data collection for Chapter 2. Julie Colvin, Juyun Lim, and Alexa Pullicin were involved with the research design and data analysis of Chapter 2. Chapter 2 was written by Julie Colvin and Juyun Lim with inputs by Alexa Pullicin. TABLE OF CONTENTS Page 1. General Introduction ........................................................................................................1 1.1 Functions of the Gustatory System in Humans ......................................................1 1.2 Peripheral Anatomy of the Human Gustatory System ...........................................2 1.2.1 Papillae ........................................................................................................3 1.2.2 Taste Buds ..................................................................................................4 1.2.3 Taste Receptors ...........................................................................................5 1.2.4 Nerves ........................................................................................................6 1.2.5 Dysfunction of the Peripheral Gustatory System ......................................6 1.3 Previous Studies on Regional Differences in Taste Response ...............................9 1.3.1 Tongue Maps: Misinterpretations and Clarifications ..................................9 1.3.2 Regional Differences in Taste Sensitivity .................................................10 1.3.3 Regional Differences in Taste Responsiveness ........................................11 1.3.4 Stimuli Concentration ...............................................................................12 1.3.5 Umami Stimuli ..........................................................................................13 1.4 Regional Differences for Alternative Tastes ........................................................15 1.4.1 Taste of Fat ................................................................................................15 1.4.2 Taste of Complex Carbohydrates ..............................................................16 1.5 The Effects of Intraoral Movement on Taste Perception .....................................18 1.5.1 Intraoral Processing ...................................................................................19 1.5.2 Stimuli Spread ...........................................................................................20 1.5.3 Other Effects of Intraoral Movements ......................................................21 1.6 Study Objectives ..................................................................................................22 TABLE OF CONTENTS (CONTINUTED) Page 2. Regional Differences in Taste Responsiveness: Effects of Taste Quality and Tasting Mode ......................................................................................................................24 2.1 Abstract ................................................................................................................26 2.2 Introduction ..........................................................................................................27 2.3 Materials and Methods .........................................................................................30 2.3.1 Subjects .....................................................................................................30 2.3.2 Stimuli .......................................................................................................31 2.3.3 Experimental procedure ............................................................................33 2.3.4 Data analysis .............................................................................................35 2.4 Results ..................................................................................................................36 2.4.1 Experiment 1: passive tasting ...................................................................36 2.4.2 Experiment 2: active tasting ......................................................................38 2.4.3 Impact of tasting mode on regional differences in taste responsiveness across stimuli ......................................................................................................38 2.5 Discussion