Respiratory rhythm and multisensory perception

Introduction: The brain continuously processes information coming from both the external environment and visceral signals generated by the body. This constant information exchange between the body and the brain allows rhythmic signals originating from the heart and lungs, among others, to influence perception. In previous work, we have shown that cardiac cycle phase interacts with multisensory integration, i.e., the non-linear combination of information coming from multiple senses. Here, we investigated respiratory modulations of reaction times and multisensory integration in a simple detection task. Methods: Forty healthy participants were presented with unimodal (Auditory, Visual, Tactile) and bimodal (Audio-Tactile, Audio-Visual, Visuo-Tactile) stimuli while respiratory activity was recorded. Linear mixed effects models were performed on reaction times and the Race Model Inequality approach was employed to quantify multisensory integration, with a specific focus on respiratory phases. Results: First, respiration was found to significantly modulate reaction times irrespective of the stimulus type, with distinct temporal dynamics for unimodal and bimodal stimuli. Notably, reaction times were slower during the expiration-to-inspiration phase. Then, the Race Model Inequality analysis revealed higher multisensory integration for Audio-Tactile and Audio-Visual stimuli during expiration-toinspiration phase. Participants also adapted their respiratory cycle, as their response onsets preferentially occurred during early expiration. Discussion: These findings indicate that respiration is not merely a bottom-up mechanism but is actively adjusted to optimize the signalto-noise balance between interoceptive and exteroceptive signals. From a predictive processing perspective, these results suggest that respiration acts as a "master clock" aligning external information sampling with fluctuating states of neural excitability. This intricate interplay between respiration and neural processes sheds light on the dynamic nature of multisensory integration and its modulation by peripheral factors.