Cardio-respiratory interactions in interoceptive perception: The role of heartbeat-modulated cortical oscillations
The cardiovascular and respiratory systems are anatomically and functionally integrated within the cardio-respiratory system. This close connection suggests that breathing continuously shapes cardiac interoceptive perception. Previously, we demonstrated cardio-respiratory interoceptive interactions in the heartbeat-evoked potential, a neural marker of cortical processing of cardiac signals. Specifically, we observed enhanced late heartbeat-evoked potential positivity and greater interoceptive accuracy during exhalation compared to inhalation in participants engaged in cardiac interoceptive tasks. Here, we extended these findings to the time-frequency domain by reanalysing our previous dataset. We investigated heartbeat-modulated cortical oscillations, examining power, inter-trial coherence, and functional connectivity across the respiratory cycle at rest, during a cardiac interoceptive task (heartbeat counting), and an exteroceptive control task (cardiac-tone counting). Results revealed that during the heartbeat counting task, late heartbeat-related power, inter-trial coherence, and functional connectivity increased during exhalation compared to inhalation, particularly in the alpha and theta frequency bands. These effects were primarily localized to right fronto-centro-parietal electrodes. Furthermore, we identified interactive relationships between heartbeat-evoked potential and heartbeat-modulated cortical oscillations in the alpha band that predicted interoceptive accuracy. These relationships were independent of cardiac physiology and were absent in the exteroceptive task. We proposed a model of cardio-respiratory interactions within the framework of interoceptive predictive coding, suggesting that these interactions occur at multiple levels of the interoceptive hierarchy: peripheral, brainstem, and cortical. Our interpretation highlights the role of heartbeat-related alpha-band modulations in enhancing the precision-weighting of cardiac prediction errors, thereby facilitating attentional allocation to interoceptive signals and the suppression of task-irrelevant distractors, particularly during exhalation.