The Insular Cortex: Neuroanatomical and Functional Insights into Interoception, Emotion, and Self-Awareness

The primate posterior insula is the terminus of a phylogenetically novel ascending pathway encoding the physiological state of the body or interoception. An increasingly complex posterior-to-anterior integration within insula culminates into a representation of subjective corporal, emotional and cognitive feelings in the anterior insula. This region contains the von Economo neuron (VEN), an atypical large spindle-shaped projection neuron that is selectively depleted in psychiatric reductions of self-conscious feelings. Our lab examines the anatomical and functional organization substantiating the role of the insula and the autonomic system in subjective feelings. We demonstrated that the insula in macaque monkeys is divided into 13 sharply-delimited architectonic areas that have each a distinct pattern of neuronal connections. These connections supports the idea of a posterior-to-anterior integration with high-order sensory and limbic activities. We provided optogenetics, microstimulation, functional imaging and tract-tracing evidence in macaques that the anterior insula is a motor output stage for the control of sympathetic and parasympathetic premotor and perhaps preganglionic nuclei. We demonstrated that the VEN occurs in only one architectonic area of the anterior insula in macaques (an “elemental” localization à la Brodmann) and contributes major descending projections. This suggests that the VEN could be the autonomic equivalent of the giant Betz cell controlling voluntary skeletal movements. In comparison with macaques, the VEN occurs in three adjacent architectonic areas in humans, suggesting major evolutionary optimization towards the emergence of human feelings seen here as an abstract perception of bodily homeostasis in an increasingly more controllable environment and interdependent society.