Interoception refers to how we perceive our body’s internal state, based on the sensory signals coming from various organs and internal structures. These signals reach the central nervous system (CNS) and allow the body to maintain homeostasis through reflexes (e.g., the baroreflex), motivational drives (e.g., hunger and thirst), and explicit bodily sensations (e.g., shortness of breath, bladder fullness, or gastric pain). All of these can prompt us to adopt certain behaviors or carry out specific actions (Quadt L et al., 2018).
To understand the link between interoception and illness, we need to briefly introduce the concept of the predictive processing model. This model suggests that the brain acts like a hierarchical “prediction machine.” Instead of building representations solely from raw sensory data, the brain uses predictions to anticipate incoming information and only updates its internal model when there are meaningful mismatches, thus minimizing “prediction errors.” This process helps the brain save energy, respond more quickly, anticipate events, and make decisions when there is uncertainty (Sprevak M & Smith R, 2023).
Research indicates that certain aspects of interoception are disrupted in people with chronic conditions—particularly interoceptive sensitivity (confidence in detecting and interpreting interoceptive signals) and, to some degree, interoceptive accuracy (actual ability to detect and interpret these signals) (Locatelli G et al., 2023). In a healthy state, interoceptive signals rarely reach conscious awareness unless we deliberately focus on them, because they fall within expected ranges and are processed automatically. Interoceptive sensations become noticeable primarily when these signals are unexpected, creating significant enough “prediction errors” to cross the threshold into consciousness. We label interoceptive sensations as “symptoms” when our best guess is that abnormal causes—linked to illness—explain these signals (Quadt L et al., 2018).
Both fatigue and pain, two of the most frequent symptoms in chronic conditions, emerge from incoming interoceptive information (Quadt L et al., 2018; Ceunen E et al., 2016). From a Bayesian perspective, many illness-related behaviors, including persistent fatigue, may continue over time due to distorted beliefs about the CNS’s ability to control bodily states predictively. Early changes in interoception during disease onset feed back into brain pathways, with high cortisol levels disrupting N-methyl-D-aspartate receptor function—important for forming and updating belief systems (Nair A & Bonneau RH, 2006). This feedback loop might lead to a metacognitive belief that the system can’t properly regulate internal states, because there is an ongoing mismatch (prediction error) between the states the brain expects (based on these beliefs) and the states it actually perceives. Relying on sickness behaviors and experiencing prolonged fatigue could be seen as an adaptive response to these “dysfunctional” regulatory evaluations—essentially, the system fails to reduce interoceptive prediction errors (Quadt L et al., 2018).
In the case of pain, it might not seem logical that paying close attention to internal sensations could help someone who suffers from it. However, trying to completely ignore or suppress pain awareness can be counterproductive. For individuals who engage in high levels of “catastrophic thinking” about pain, mindfulness-based coping strategies may be more helpful than simple distraction. From a behavioral standpoint, interoception can contribute to persistent pain more through learned avoidance of internal signals than through increased focus on bodily sensations (Gnall KE et al., 2024).
Finally, to emphasize how interoception may influence chronic illness and homeostatic regulation via the autonomic nervous system, note that multiple CNS areas and nuclei handle interoceptive signals, regulate autonomic responses, generate emotional representations, and drive adaptive behaviors:
1. Nucleus of the Solitary Tract (NTS): Located in the brainstem, it is where interoceptive signals from vagal and spinal nerves converge. It’s essential for homeostatic control of blood pressure, heart rate, and breathing.
2. Parabrachial Complex: Relays interoceptive signals from the NTS to higher brain regions like the thalamus, and is also involved in rapid autonomic responses related to pain and temperature regulation.
3. Periaqueductal Gray (PAG): Integrates interoceptive signals and coordinates them with autonomic outputs, regulating defensive and autonomic responses such as pain modulation, and cardiovascular and respiratory control.
4. Hypothalamus: Combines interoceptive signals from the NTS with hormonal signals about the body’s internal state and then coordinates endocrine responses with major effects on the autonomic system, such as regulating body temperature, fluid balance, and hormone levels.
5. Thalamus: Operates as a relay station, directing interoceptive information from the NTS and parabrachial complex to the insular cortex and the cingulate cortex; it also aids in processing both nociceptive and interoceptive signals.
6. Insular Cortex (IC): The posterior insula receives primary visceral sensory data from the thalamus and converts it into conscious representations of internal states. The anterior insula integrates this information with emotional processes to regulate autonomic responses (e.g., changes in heart rate and sweating under stress).
7. Anterior Cingulate Cortex (ACC): Forms a functional network with the anterior insula and the hypothalamus, involved in guiding motivated behaviors and autonomic adjustments, such as those related to stress or physical effort.
By bringing together interoceptive and internal-state processing, autonomic responses, emotional processes, conscious representations of bodily states, and adaptive behaviors, it’s clear how crucial interoception is to chronic conditions and to the normal function of the autonomic nervous system (Quadt L et al., 2018; Quigley KS et al., 2021).
Bibliography
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