Cardiac and gastric interoception have distinct neural substrates

Abstract Interoception, or an awareness of the internal body state, guides agents in adaptive behavior by informing them of ongoing bodily signals, such as heart rate or energy status. However, it is still unclear whether the human brain represents the differences in the subjective experience of interoception differently. Hence, we directly compared the neural activation for cardiac (awareness related to heartbeats) and gastric (awareness related to the stomach) interoception in the same population (healthy human, N = 31). Participants were asked to focus on their heart and stomach sensations to be aware of interoception in a magnetic resonance imaging scanner. The results indicated that neural activation underlying gastric interoception encompassed larger brain regions, including the occipitotemporal visual cortices, bilateral primary motor cortex, primary somatosensory cortex, left orbitofrontal cortex, and bilateral hippocampal regions. Cardiac interoception, however, selectively activated the right anterior insula extending to the frontal operculum more compared to gastric interoception. Moreover, our detailed analyses focusing on the insula, the most relevant region for interoception, revealed that the left dorsal middle insula encoded cardiac and gastric interoception in different activation patterns but not the posterior insula. Our results demonstrate that cardiac and gastric interoception have distinct neural substrates; in particular, the selective brain activation may reflect differences in the functional roles of cardiac and gastric interoception. Significance statement Interoception, subjective senses that arise from within the body, plays a critical role in maintaining adaptive behavior by informing of the ongoing bodily states, such as heart rate and energy status. Although interoception has various characteristics depending on its source signals, previous neuroimaging studies have extensively used cardiac interoception (senses related to heartbeats), making it unclear whether the brain differently encodes diverse experiences of interoception. Here, we demonstrate that cardiac interoception and gastric interoception (senses related to the stomach) have distinct neural substrates by combining mass-univariate analysis with multivoxel pattern analysis for fMRI data. Our findings suggest that the selective brain activation may reflect differences in the functional roles of cardiac and gastric interoception.