An Examination of the Neural Correlates of Interoceptive Processes in the Macaque Monkey
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An Examination of the Neural Correlates of Interoceptive Processes in the Macaque Monkey Dissertation zur Erlangung des Grades eines Doktors der Naturwissenschaften der Mathematisch-Naturwissenschaftlichen Fakultät und der Medizinischen Fakultät der Eberhard-Karls-Universität Tübingen vorgelegt von Renee Elizabeth Hartig aus Smithtown, New York, United States of America September 2019 Tag der mündlichen Prüfung: 10. Dezember 2019 Dekan der Math.-Nat. Fakultät: Prof. Dr. W. Rosenstiel Dekan der Medizinischen Fakultät: Prof. Dr. I. B. Autenrieth 1. Berichterstatter: Dr. Henry C. Evrard 2. Berichterstatter: Prof. Andreas Bartels 3. Berichterstatter: Prüfungskommission: Dr. Henry C. Evrard Prof. Andreas Bartels Prof. Cornelius Schwarz Prof. Nikos K. Logothetis vii I hereby declare that I have produced the work entitled “An Examination of the Neural Correlates of Interoceptive Processes in the Macaque Monkey” submitted for the award of a doctorate, on my own (without external help), have used only the sources and aids indicated and have marked passages included from other works, whether verbatim or in content, as such. I s wear upon oath that these statements are true and that I have not concealed anything. I am aware that making a false declaration under oath is punishable by a term of imprisonment of up to three years or by a fine. Tübingen, 30 September 2019 ________________ Renee Elizabeth Hartig viii To the wise that came before my time ix x ABSTRACT Several well-established methods exist for recording and measuring the underlying signals of the brain. Methods such as electrophysiology and fMRI, when taken together, have the capacity to disclose local and global neuronal activity. Here, both techniques were employed to refine the working functional model of the insular cortex, a recipient of sensory afferents relaying information about the body’s physiological state. This dissertation serves to extend the current knowledge relating to the sensory afferent pathways relaying gustatory and interoceptive information to the brain, with special considerations of the role of the insular cortex. A series of fMRI experiments were conducted in the anesthetized macaque; whereby, responses to different types of interoceptive stimulation were measured (e.g. lower gastrointestinal distention, cutaneous thermal stimulation, auricular vagus nerve stimulation, and taste). The gross anatomical localization of these functions were mapped, providing a foundation for subsequent electrophysiological sampling across the insula. Using these methods, our results revealed a topographic organization of multi-modal interoceptive responses and the evidence garnered was analyzed within the context of insular cortex connectivity and its association with limbic and higher-order cortical areas. Our results support previous evidence of a topographic representation of interoceptive afferents in the human insula and contribute to the working model of insular cortex function in non-human primates. The manner in which interoceptive information is organized may disclose how upstream regions integrate sensory information to form a conscious percept of the body’s physiological state, shaping cognition, and contribute to emotional embodiment. The present work serves as a basis for mapping functional responses with more involved paradigms designed to assess the emotional and cognitive responses to interoceptive sensations in the awake behaving state. xi xii CONTENTS ABSTRACT --------------------------------------------------------------------------------------------------------- XI ABBREVIATIONS -------------------------------------------------------------------------------------------------- 3 SYNOPSIS -------------------------------------------------------------------------------------------------------------- Channeling the Senses -------------------------------------------------------------------------------------------- 5 Building Upon the Senses ---------------------------------------------------------------------------------------- 11 Scientific Objectives ---------------------------------------------------------------------------------------------- 12 State of the Art ---------------------------------------------------------------------------------------------------- 14 Dynamic Brain States ------------------------------------------------------------------------------------------- 14 Functional Magnetic Resonance Imaging -------------------------------------------------------------------- 15 Electrophysiology ----------------------------------------------------------------------------------------------- 16 Overview ------------------------------------------------------------------------------------------------------------ 17 Part 1: Functional Imaging during Interoceptive Stimulation --------------------------------------------- 17 Part 2: Interotopic Maps ---------------------------------------------------------------------------------------- 18 Part 3: Functional Connectivity ------------------------------------------------------------------------------- 19 A Step Forward --------------------------------------------------------------------------------------------------- 19 Bibliography ------------------------------------------------------------------------------------------------------- 22 Declaration of Contributions ----------------------------------------------------------------------------------- 29 1 Appended Manuscripts 1. NORMALIZING PRIMATE NEUROIMAGING RESULTS ------------------------------------------- 31 2. THE NON-HUMAN PRIMATE CORTICAL TASTE REPRESENTATION ------------------------- 31 3. BOLD CORRELATES OF RECTAL DISTENTION IN THE ANESTHETIZED MACAQUE ----- 69 4. THE INSULAR CORTEX’S INTEROTOPIC MAP ----------------------------------------------------- 83 ACKNOWLEDGEMENTS ------------------------------------------------------------------------------------- 125 2 ABBREVIATIONS ABVN auricular branch of the vagus nerve ACC anterior cingulate cortex AIC anterior insular cortex ANOVA analysis of variance ANS autonomic nervous system AP anteroposterior axis BOLD blood-oxygen-level-dependent CN cranial nerve CNS central nervous system DV dorsolateral axis ECG electrocardiogram EGG electrogastrogram fMRI functional magnetic resonance imaging FOV field-of-view FWHM full-width at half-maximum HPC heat-pinch-cold cell Idfa/dAIC dorsal fundus of the anterior insular cortex Idfm dorsal fundus of the mid-insular cortex Idfp dorsal fundus of the posterior insular cortex GLM General Linear Model LFP local field potential MCC midcingulate cortex MDvc mediodorsal thalamic nucleus ventrocaudal portion 3 MDEFT modified driven equilibrium Fourier transform ML mediolateral axis MUA multi-unit activity NHP non-human primate NTS nucleus tractus solitarius PAG periaqueductal gray PBN parabrachial nucleus PGA Primary Gustatory Area PIC Primary Interoceptive Cortex PFC prefrontal cortex PSFS peripheral suction fluid stimulator RD rectal distention Ri retro-insula ROI Region-of-Interest SDF spike density function ssGLS suction-sealed gustolingual stimulator vAIC ventral Anterior Insular Cortex VEN von Economo Neuron VMb ventromedial thalamic nucleus basal portion VMpo ventromedial thalamic nucleus posterior portion 4 SYNOPSIS “Sense-objects are always present, and thus when a sense organ—the subtle matter that allows you to see, hear, and so forth— develops, an eye consciousness, ear consciousness, nose consciousness, tongue consciousness, or body consciousness will be produced.” (Dalai Lama, 2000) CHANNELING THE SENSES The brain is an avid processor of the world around us and the world within us. The processing of these environments, and the signals arising from them, is crucial for survival and the maintenance of a healthy, balanced life. This dissertation examines the representation of different sensory modalities in the brain, with particular attention to signals arising from the body. The underlying neural activity representing these sensory processes was analyzed to refine the concept of a somatotopographically organized insular cortex in the macaque monkey, a region with multiple functional domains encoding different aspects of bodily processing. The evidence presented here was compared to the topographic organization of the human insula, as determined by fMRI, and to prior tract-tracing studies previously targeting thalamic nuclei known to project to the insula. From this comparative research, we learn that the topographic innervation of afferents is conserved from the spinal cord to the cortex and that distinct anatomical subregions support the integration of multi-modal information. While a plethora of functional modules exist within the neuroanatomical construct of the brain, this intricate system is often parsimoniously described for general education purposes. What has been commonly taught to students about the central nervous system (CNS) largely concerns the input of information to the brain and outputs in terms of emotions, behavior and physiological changes. There are five classical senses everyone learns by adulthood: taste, touch, smell, vision and hearing. It is generally understood that the brain receives visual input from the eyes, auditory 5 input from the ears, taste input from the mouth, olfactory input from the nose and tactile input from the skin. By this framework, each sense has its own specialized organ for transducing the relevant information. But, to consider the processing of sensory information only within this framework would surely