Rhythmic nasal air-puff as a potential noninvasive brain stimulation approach for stabilizing integrated brain...

Breathing modulates neural oscillations and large-scale brain network organization, partly through mechanical stimulation of olfactory sensory neurons (OSNs). To investigate the mechanosensory contribution of olfactory input, we compared rhythmic, odorless nasal air-puff stimulation (~0.2Hz) with oral breathing during resting-state fMRI in healthy adults (n = 21). Dynamic functional connectivity was analyzed using a hidden Markov model (HMM) applied to BOLD fluctuations centered on the stimulation frequency. Four recurrent brain states were identified, spanning a continuum from highly segregated to globally integrated configurations. Relative to oral breathing, nasal air-puff stimulation increased the fractional occupancy and lifetime of the integrated state characterized by higher global and local efficiency and lower modularity, reduced the overall switching rate, and selectively reshaped transition probabilities away from fragmented configurations. These effects partially reproduced key features observed during natural nasal breathing in our prior work, suggesting that rhythmic mechanosensory activation of OSNs contributes to the stabilization of integrated large-scale brain states. The findings support a respiration-entrained framework in which olfactory input contributes to the organization and temporal stability of large-scale brain networks.