Exploring the dynamic interplay between cardiac interoception, focus of attention, and respiration

The Heartbeat-Evoked Potential (HEP) is an EEG voltage fluctuation that reflects the cortical processing of cardiac signals. The predictive coding model of interoceptive perception posits that HEPs represent a precision-weighting process of prediction errors related to heartbeat sensations. Recent studies have found that HEP amplitude and cardiac interoceptive accuracy are higher during exhalation compared to inhalation, possibly since cardiac-related sensations of heartbeats occurring during inhalation are suppressed, while those occurring during exhalation are amplified by attention. To explore the dynamic interactions between cardiac interoception, focus of attention, and respiration, we developed a new experimental paradigm. We assessed HEP activity in 34 volunteers (28 ± 4 years) during four tasks involving either interoceptive or exteroceptive attention, and focused on either the cardiac or the respiratory system. The Heartbeat Counting Task (HCT) and the Breath Counting Task (BCT) were the interoceptive tasks, while the Cardiac-Tone Counting Task (C-TCT) and the Breath-Tone Counting Task were the exteroceptive tasks (B-TCT).Results showed that the HCT induced significant HEP increases compared to both the C-TCT and the BCT over frontal-central electrodes in a late HEP t ime-window. Crucially, observed HEP amplitude increases during the HCT compared to both the C-TCT and the BCT were driven by HEPs recorded during the exhalation phase of respiration, with minimal contributions from HEPs recorded during inhalation. These findings showed that HEP amplitude reflects a precision-weighting process of prediction errors specifically modulated by attention directed towards cardiac sensations, and that the exhalation phase of respiration enables this precision-weighting process.