![]() ![]() ![]() Īs noted earlier, gustatory (taste) receptors have variously been considered as interoceptors or exteroceptors. Although some central neurons may have inherent chemoreceptive sensitivity, it also appears that brain glial cells (astrocytes), that are chemically (but non-synaptically) coupled to neurons, may mediate the sensitivity to local states such as pCO 2/pH, glucose sensitivity and Na + sensitivity that participate in controlling hunger and thirst among other functions. ![]() Central sensitivity to metabolic conditions is thus conveyed jointly by both peripheral and central chemoreceptors. Both central and peripheral osmoreceptors, for example, that are sensitive to the local osmotic pressure (cellular dehydration), are important in eliciting thirst and other drivers of metabolic adjustments to compensate for body water imbalance. There is also a wide range of chemoreceptors that are sensitive to a variety of body conditions and metabolic states these include central and peripheral glucoreceptors, thermoreceptors, gustatory receptors, and osmoreceptors. This chemosensitivity is likely achieved, at least in part, through specific ion channels, such as the Twik-related acid-sensitive K + channels 1 and 3 (TASK1/TASK3), that are sensitive to acidosis and pO 2. A classic example is the carotid body chemoreceptor sensitivity to pCO 2, pH, and to a lesser extent pO 2, in the regulation of respiration and cardiovascular reflexes. 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.)Ĭhemoreceptors are widespread and are sensitive to a wide variety of chemical states or substances. Each component contributes to the next, although most processing of interoceptive signals occurs beyond the conscious awareness of the organism. 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). One important focus will be on the interactions between interoceptive afferent signaling and the coupled, reciprocal descending regulatory systems that comprise coherent circuits for adaptive regulation. We focus on recent developments – and gaps – in our understanding of ascending and descending pathways that are essential for interoceptive processing across human and other animal species. This review considers the neural pathways and neural circuits of interoception. Contemporary conceptualizations often consider that interoception entails the integrative interpretation of internal and external stimuli – in the cognitive/emotional context – to derive an overall physiological representation of the state of the body, including conscious and nonconscious aspects. However, interoception is now generally considered to entail far more than only visceroception, and to include the emotional and cognitive sequelae of, and conversely, contributions to, internal bodily states and regulation. The term visceroception could perhaps characterize the classic view. Among the most salient evolutions in our concepts of interoception is the considerable broadening of the meaning of the term. Gustation and olfaction likely play a role in interoceptive processes. ![]() Gustation and olfaction, however, are special visceral senses – they share common biochemical markers with general visceral afferents, and project to central areas implicated in interoception (section on Ascending Pathways). For example, gustation is not always considered to be an interoceptive sense (although lower alimentary receptors may be). Much has changed in our understanding of interoceptive processes since Sherrington’s time. Sherrington contrasted interoception to exteroceptive sensing, or the sensitivity to stimuli emanating from outside the body (including odors), which could yield projicience – an explicit self-referential representation of sensory stimuli occurring far away from the body. The notion of an internal sense of the body (e.g., coenesthesis or somesthesis) dates back centuries, although it was Sherrington (1906) who first introduced the term interoceptive (see Glossary) to refer to senses that convey information on the internal state of the body. ![]()
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