An Examination of the Neural Correlates of Interoceptive Processes in the Macaque Monkey

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.