The interplay between focus of attention, respiratory phases, and the Heartbeat Evoked Potential

The Heartbeat Evoked Potential (HEP) is an EEG fluctuation that reflects the cortical processing of cardiac signals. HEP amplitude increases during various tasks involving cardiac interoception. Recent research has also indicated that HEP amplitude and cardiac interoceptive accuracy are higher during exhalation compared to inhalation. This difference may be due to the suppression of heartbeat-related sensations during inhalation and the amplification of sensations during exhalation through attentional mechanisms. Despite significant advancements in HEP research, the interactions between the HEP, interoceptive attention, and respiration are still unclear. In this study, we developed a novel experimental paradigm to investigate the relationship between HEP amplitude and respiratory phases during tasks that involve attention to cardiac interoception, non-cardiac interoception (specifically, respiration), and exteroceptive stimuli. The tasks included the Heartbeat Counting Task and the Breath Counting Task as interoceptive tasks, as well as the Cardiac-Tone Counting Task and the Breath-Tone Counting Task as exteroceptive tasks. Results demonstrated significant increases in HEP amplitude during the Heartbeat Counting Task compared to the Cardiac-Tone Counting Task and the Breath Counting Task, mostly observed over fronto-central electrodes in a late time-window. Notably, the amplitude increases during the Heartbeat Counting Task were primarily driven by HEPs recorded during exhalation, while inhalation had minimal impact. These findings align with the predictive coding model of interoceptive perception, suggesting that HEP amplitude reflects a precision-weighting process of prediction errors related to cardiac sensations that is specifically influenced by attention directed toward the heart. Furthermore, our findings emphasize the crucial role of exhalation in this precision-weighting process. These results may have considerable implications for the development of respiratory interventions to fine-tune cardiac interoception.