Cardio-respiratory interactions in interoceptive perception: The role of heartbeat-modulated cortical oscillations

The cardiovascular and respiratory systems are anatomically and functionally integrated, suggesting that breathing continuously influences cardiac interoception. Previously, we demonstrated that the heartbeat-evoked potential (HEP), a neural marker of cardiac signal processing, is modulated by respiration, with enhanced late HEP positivity and increased interoceptive accuracy during exhalation. Here, we reanalysed our previous dataset in the time-frequency domain to investigate heartbeat-modulated cortical oscillations across respiratory phases during rest, cardiac interoception (heartbeat counting), and an exteroceptive control task. During heartbeat counting, exhalation was associated with increased late heartbeat-modulated alpha- and theta-band power and inter-trial coherence over fronto-parietal electrodes, compared with inhalation. Heartbeat-modulated alpha activity was related to HEP amplitude and predicted interoceptive accuracy. Exploratory analyses also indicated enhanced heartbeat-modulated functional connectivity during exhalation. These effects could not be accounted for by cardiac physiology alone and were absent during exteroception. We propose a mechanistic account of cardio-respiratory interactions grounded in interoceptive predictive coding, suggesting that exhalation enhances precision-weighting of cardiac signals by facilitating attentional allocation to interoceptive signals and suppressing task-irrelevant distractions.