Nasal respiration entrains neocortical long-range gamma coherence during wakefulness

Recent studies have shown that slow cortical potentials in archi-, paleo- and neocortex can phase-lock with nasal respiration. In some of these areas, gamma activity (γ: 30-100 Hz) is also coupled to the animal's respiration. It has been hypothesized that these functional relationships play a role in coordinating distributed neural activity. In a similar way, inter-cortical interactions at γ frequency have also been associated as a binding mechanism by which the brain generates temporary opportunities necessary for implementing cognitive functions. The aim of the present study is to explore whether nasal respiration entrains inter-cortical functional interactions at γ frequency during both wakefulness and sleep. Six adult cats chronically prepared for electrographic recordings were employed in this study. Our results show that during wakefulness, slow cortical respiratory potentials are present in the olfactory bulb and several areas of the neocortex. We also found that these areas exhibit cross-frequency coupling between respiratory phase and γ oscillation amplitude. We demonstrate that respiratory phase modulates the inter-cortical gamma coherence between neocortical electrode pairs. On the contrary, slow respiratory oscillation and γ cortical oscillatory entrainments disappear during non-rapid eye movement and rapid eye movement sleep. These results suggest that a single unified phenomenon involves cross-frequency coupling and long-range γ coherence across the neocortex. This fact could be related to the temporal binding process necessary for cognitive functions during wakefulness.