Neural Circuits of Interoception

Abstract

The present paper considers recent progress in our understanding of the afferent/ascending neural pathways and neural circuits of interoception. Of particular note is the extensive role of rostral neural systems, including cortical systems, in the recognition of internal body states, and the reciprocal role of efferent/descending systems in the regulation of those states. Together these reciprocal interacting networks entail interoceptive circuits that play an important role in a broad range of functions beyond the homeostatic maintenance of physiological steady-states. These include the regulation of behavioral, cognitive, and affective processes across conscious and nonconscious levels of processing. We highlight recent advances and knowledge gaps that are important for accelerating progress in the study of interoception.

Keywords: autonomic; efferent; homeostasis; interoceptive awareness; visceral afferent.

Figure 1.. The Continuum of Interoception.

Interoception is a neural process that traverses sensors (e.g., mechanoreceptors, thermoreceptors, chemoreceptors, osmoreceptors, humoral receptors, glucoreceptors, and free nerve endings), pathways (e.g., vagal, cranial, sacral, spinothalamic, and somatosensory), networks (e.g., central and peripheral autonomic, enteric, thalamocortical, hypothalamic, limbic, sensorimotor, salience, and default), circuits (e.g., appetitive, affective, arousal, thermal, nociceptive, cognitive, social, and threat), and awareness (e.g., detection, attention, insight, magnitude, discrimination, accuracy, and sensibility). Each component contributes to the next, although most processing of interoceptive signals occurs beyond the conscious awareness of the organism. Further, interoceptive awareness relies on circuit-based representations of the internal bodily self (e.g., ‘my body’: manikin at top right) and differs substantially from other circuit-based representations of other living objects (e.g., ‘dog’, ‘plant’ etc.)

Figure 2.. Brain Regions Involved in Interoceptive Processing.

There is a cross-species gap in our understanding of how interoceptive signals are relayed through the central nervous system from the body. In humans, the role of cortical and limbic regions is well characterized, with less emphasis on the transmission of interoceptive signals from the body to brainstem regions (e.g., NTS, PB). In animal models including rodents (as illustrated here), the role of interoceptive signal transmission from the body to brainstem regions (e.g., NTS) is well detailed, with less emphasis on the role of signal transmission to higher cortical regions. Ascending arrows denote afferent signal transmission; descending arrows denote efferent signal transmission. Abbreviations: Amy, amygdala; BG, basal ganglia (including striatum and caudate); CVO, circumventricular organs including the subfornical organ (SFO), organum vasculosum of the lamina terminalis (OVLT), and the area postrema (AP); DMN, dorsal motor nucleus; Hipp, hippocampus; HPA, hypothalamus and pituitary; Ins, insular cortex; mPFC, medial prefrontal cortex (including infra- and pre-limbic cortex); NA, nucleus ambiguus; NTS, nucleus tractus solitarius; OFC, orbitofrontal cortex; PAG, periaqueductal grey; PB, parabrachial nucleus; RVLM, rostral ventrolateral medulla; SI/II, primary and secondary somatosensory cortex; vmPFC, ventromedial prefrontal cortex.