Parallel occurrence of theta and respiration-coupled network oscillations throughout the mouse brain

Slow brain oscillations are usually coherent over long distances and are thought to constitute a means to link distributed cell assemblies. In mice, theta oscillations (4-12 Hz) stand as one of the most studied global slow rhythms. Previous research has suggested that theta takes part in interregional communication required for cognitive functions. However, mice often breathe at theta frequency, and we have recently reported that nasal respiration leads to synchronous network oscillations that are independent of theta. Namely, we showed that respiration-coupled oscillations occur in the hippocampus, prelimbic cortex, and parietal cortex, suggesting that, as theta, respiration-coupled oscillations are also global. In the present work, we sought to extend these findings by tracking respiration while simultaneously recording local field potentials from 15 brain regions of freely moving mice during exploration and REM sleep. We report that respiration-coupled rhythms can be detected in parallel with theta in widespread neocortical regions, from prefrontal to visual areas, and also in subcortical structures such as the thalamus, amygdala and ventral hippocampus. Though both rhythms occur simultaneously, respiration-coupled oscillations are more dominant in frontal regions while theta oscillations prevail in more caudal networks. We conclude that respiration-coupled oscillations are a global brain rhythm suited to entrain distributed networks into a common regime. This pattern might have escaped attention in previous studies due to the absence of respiration monitoring, its similarity with theta oscillations, and its highly variable peak frequency. It should, however, be considered as a widespread signal and potential mechanism of long-range network communication.