The Emerging Science of Interoception: Sensing, Integrating, Interpreting, and Regulating Signals within the Self

Abstract

Interoception refers to the representation of the internal states of an organism, and includes the processes by which it senses, interprets, integrates, and regulates signals from within itself. This review presents a unified research framework and attempts to offer definitions for key terms to describe the processes involved in interoception. We elaborate on these definitions through illustrative research findings, and provide brief overviews of central aspects of interoception, including the anatomy and function of neural and non-neural pathways, diseases and disorders, manipulations and interventions, and predictive modeling. We conclude with discussions about major research gaps and challenges.

Keywords: autonomic; insula; parasympathetic; spinal; sympathetic; vagal.

Figure 1.. Illustrative diagram of sample ascending neural pathways of interoception.

This diagram only describes the ascending neural pathways connecting the peripheral internal organs with the brain. The non-neural ascending pathways are not included in this figure. Interoceptive sensory signals generated by the peripheral organs may be detected by molecular sensors or receptors, called interoceptors, present at the termini of the peripheral sensory ganglia. The sensory ganglia residing in the cranial/vagal pathways, such as nodose or jugular ganglia, often send projections to the nucleus tractus solitarii (NTS) of the brainstem through vagal afferents, sometimes referred to as ‘parasympathetic afferents.’ The sensory ganglia located along the spinal nerve pathway, often called dorsal root ganglia, send projections through the dorsal column of the spinal cord into the brain via spinal afferents, sometimes referred to as ‘sympathetic afferents.’

Figure 2.. Brain regions involved in central processing of interoceptive signals.

The diagrams in this figure depict some of the various brain regions involved in central interpretation, integration, and regulation of interoceptive information. The figure on the left is a mid-sagittal view of the human brain, highlighting brain regions implicated in central processing of interceotion. The figure on the right is a lateral-saggital view of the brain highlighting the insula cortex, including anterior insular cortex (AIC) and posterior insular cortex (PIC), as well as somatonsensory cortex (SI/SII). Within the brain, interoceptive information is often first processed in subcortical structures such as the medial nucleus of the solitary tract (NTS), the parabrachial nucleus (PB), and then the ventromedial nucleus of the thalamus. Neurons in these structures project to other brain regions such as the hypothalamus and eventually to the insular cortex, a critical cortical node in the interoceptive system. Primary interoceptive information relayed from the ventromedial nucleus of the thalamus projects to PIC, where integration with exteroceptive sensorimotor and proprioceptive information from SI/II most likely occurs. AIC is most strongly connected to paralimbic cortical regions such as the orbitofrontal cortex (OFC), anterior cingulate cortex (ACC), and prefrontal cortex (PFC), which may be involved in linking between interoceptive and emotional or cognitive states for further integration and interpretation, and possibly generation of regulatory signals sent back to lower brain regions involved in interoceptive descending efferent systems.

Figure 3.. Illustrative diagram of sample descending neural pathways of interoception.

This diagram only describes the descending neural pathways connecting the brain with the peripheral internal organs. The non-neural descending pathways are not included in this figure. We refer to the signals generated by the CNS, often in response to interoceptive input, to regulate the interoceptive processes as “regulating signals of interoception”. Neurons in the CNS involved in generating these regulating signals can be called central regulators of interoception. The regulating signals may be communicated to the peripheral internal organs via descending spinal or vagal/cranial efferents. The spinal efferents are also referred to as the sympathetic efferents of the autonomic nervous system as they go through the spinal cord pathway and regulate sympathetic activities. After existing the spinal cord, some of the spinal efferents synapse onto the sympathetic chain ganglia, which then directly project onto the peripheral organ cells to regulate interoceptive signals or organ function. These sympathetic chain ganglia may thus be considered as the effector neurons in the interoceptive descending neural pathway. Other spinal efferents synapse onto prevertebral ganglia instead, which may act as effector neurons and project to the peripheral organ cells. The vagal/cranial efferents, also called the parasympathetic efferents of the autonomic nervous system, typically go through the nodose or jugular ganglia bundles and make synaptic connections onto parasympathetic ganglia, which are often located near the peripheral organs and act as effector neurons to regulate peripheral organ’s interoceptive signals or organ functions.