Respiration facilitates behaviour during multisensory integration

The brain processes information from the external environment alongside signals generated by the body. Among bodily rhythms, respiration emerges as a key modulator of sensory processing. Multisensory integration, the non-linear combination of information from multiple senses to reduce environmental uncertainty, may be influenced by respiratory dynamics. This study investigated how respiration modulates reaction times and multisensory integration in a simple detection task. Forty healthy participants were presented with unimodal (Auditory, Visual, Tactile) and bimodal (Audio-Tactile, Audio-Visual, Visuo-Tactile) stimuli while their respiratory activity was recorded. Results revealed that reaction times systematically varied with respiration, with faster responses during peak inspiration and early expiration but slower responses during the expiration-to-inspiration transition. Applying the race model inequality approach to quantify multisensory integration, we found that Audio-Tactile and Audio-Visual stimuli exhibited the highest integration during the expiration-to-inspiration phase. These findings conceivably reflect respiration phase-locked changes in cortical excitability which in turn, orchestrates multisensory integration. Interestingly, participants also tended to adapt their respiratory cycles, aligning response onsets preferentially with early expiration. This suggests that, rather than a mere bottom-up mechanism, respiration is actively adjusted to maximise the signal-to-noise balance between interoceptive and exteroceptive signals.