Evaluating heartbeat perception for the investigation of the role of the insula in interoception

Interoception is usually defined as the ability to perceive signals from the internal organs of the body. This ability is often studied with the heartbeat counting task. However, there has been a lot of criticism of this task, with questions raised about what exactly it measures. The HCT is also widely used in neuroimaging studies where activity in the insula cortex during interoception is the target. The current study addresses the validity issue derived from the HCT and questions the interpretation of the activation of the insula cortex during this task. In the first experiment, the HCT was repeated multiple times to investigate whether participants' performance improved with practice. Moreover, the HCT was matched with an equivalent visual task to explore the possibility that the HCT reflects an ability to count any uncertain stimuli, regardless of the sensory domain. The results showed that participants' performance in the HCT remained stable regardless of practice. Additionally, their performance in the HCT was correlated with their performance in the visual task. Based on this, the study concludes that performance in the HCT may reflect an ability to count ambiguous stimuli rather than interoceptive stimuli. Interoceptive abilities are of particular interest in the context of psychiatric conditions and related psychological constructs. As such, in the second experiment, the study investigated the relationship between HCT performance and three of the most common questionnaires for evaluating trait anxiety, alexithymia, and depression. The results showed no robust evidence for any associations between HCT performance and these psychological traits. This suggests that the HCT is not a good tool for diagnosing psychiatric conditions and is unlikely to provide a direct measure of any impairments in interception. In the last experiment, the study investigated whether the functional activity of the insula cortex during the HCT and an exteroceptive task can be explained by its structural connectivity. By applying a gradient approach, the study found that the structural connectivity diversity of the insula cortex predicts its functional responses to both tasks. Moreover, based on the patterns of the structural connections, the insula cannot be divided into subregions following its anatomical divisions. This is an important step towards better understanding how structural connections in the brain are related to its functions. It also suggests that there is a structurally guided difference between the response patterns to the HCT and the exteroceptive control condition. Overall, the study recommends against using the HCT as a measure of interoception and does not interpret the activity of the insula cortex found during it as reflecting only interoceptive processes.