Influence de la respiration sur les rythmes du cerveau chez le Rat : une étude électrophysiologique au cours des cycles veille / sommeil

Inter-area communication requires the different brain rhythms to be coordinated across areas. This coordination can be achieved by synchronizing electrophysiological rhythms. As others, we hypothesized respiratory rhythm could act as a central clock for cerebral rhythms coordination. If true, one can expect neuronal activity to be influenced by respiration in a large brain network. We tested that by recording respiration and neuronal activity in different brain areas in the freely-moving rat during different vigilance states. In agreement with recent publications, we observed that all structures could be modulated by breathing. We provided the additional observation that such a modulation varies according to the vigilance state, each state being associated with a specific respiratory regime. Particularly, we observed a large-scale synchronization of all recorded structures on the respiratory rhythm is only observable in the calm awake state, where the breathing has a low frequency (2Hz), with a relatively high air flow. At the same time, we also observe a modulation of the fast gamma rhythm (35-80 Hz) in all areas, only in the calm awake state. To determine whether this general respiratory synchronization was a consequence of the state itself or of the respiratory regime, we sought to uncorrelated the brain state of the respiratory regime. Animals were thus recorded while breathing a CO2-enriched air, where the respiratory characteristics (frequency and amplitude) are increased compared to the normal air condition. We observed the across-areas respiratory synchronization observed in quiet state can be extended, under CO2 condition, to other vigilance states including sleep states (REM and non-REM).We show that the coordination of the brain by breathing is related to the combined effect of the amplitude and duration of inspiration. Finally, we wanted to evaluate the respective share of air flows related to breathing and central breathing control on the brain's training by breathing. We uncorrelated the animal's breathing from the air flows in the nasal cavity through a double tracheotomy experiment in the anesthetized animal. The first results seem to show that the air flows circulating in the nasal cavity during successive breaths have a preponderant part in the entrainment of the brain. In conclusion, breathing can lead to a large cortical network via the activation of the olfactory system by the air flows circulating in the nasal cavity. The optimal breathing regime for this training is slow and deep breathing. This study is important to understand how relaxation and meditation methods work on the brain.