Respiratory phase shapes brain-heart dynamics: evidence from recurrence analysis of EEG band power and heart rate.

Introduction: Respiration is increasingly recognized as a key modulator of brain-body interactions, influencing both neural and autonomic dynamics. While prior work has demonstrated respiratory-driven entrainment, it remains unclear whether distinct phases of the breathing cycle give rise to different dynamical regimes of cortical activity. Methods: In this study, we investigated respiratory-phase-dependent modulation of brain-heart interactions during controlled breathing, focusing on breath-hold periods following inhalation and exhalation. EEG band power time series and heart rate (HR) were analyzed in 15 healthy subjects. In addition to conventional spectral measures, recurrence quantification analysis was employed to characterize non-linear dynamics in cortical activity. Results: Results revealed clear respiratory-phase-dependent differences. Inhale-hold was associated with increased γ band power, higher recurrence rate, and elevated HR, whereas exhale-hold showed reduced γ activity, lower recurrence, and decreased HR. These findings are consistent with known mechanisms of respiratory sinus arrhythmia and suggest that the two conditions correspond to distinct autonomic states. From a dynamical systems perspective, increased recurrence during inhale-hold suggests more structured and constrained cortical dynamics, while reduced recurrence during exhale-hold reflects comparatively more variable activity. Discussion: Together, these findings suggest that respiratory phase modulates the organization of brain-body dynamics, potentially reflecting shifts between more stable and more flexible regimes of neural activity. This phase-dependent organization supports the view that respiration may act as a physiological mechanism for dynamically tuning brain-heart interactions, with implications for understanding the role of breathing in the modulation of neural dynamics.