Respiratory Modulation of Cortical Rhythms - Testing The Phase Transition Hypothesis.

The presence of respiration-locked sensory cortical activity has been documented in various mammalian species in recent years, including cognitively-relevant gamma oscillations (30-80 Hz). This work builds on previous evidence suggesting that respiration has a direct influence on oscillatory activity in human sensory, motor and association cortical areas. The entrainment of cortical activity patterns by respiratory phase suggests a direct influence of respiration on cognitive processing, which represents a possible neuronal mechanism behind the well-documented but unexplained effects of respiratory exercises on emotional and cognitive functions. We explore possible interpretation of those findings in the context of the cinematic view of cognition, in particular cortical phase transitions. In addition to traditional Fourier-based correlational analysis of cortical signals, we introduce Hilbert analysis, which allows to monitor rapid phase synchronization-desynchronization transitions. Our results support the hypothesis that respiration-locked cortical activity is linked to phase transitions in the cortex, measured by discontinuities of the instantaneous phase of the analytic signal determined by the Hilbert transform. Taken together, these findings suggest that respiration acts as master clock exerting a subtle but unfailing synchronizing influence on the temporal organization of dynamic cortical activity patterns and the cognitive processes they control.