Lack of respiratory coupling with neocortical and hippocampal slow oscillations.

Previous work has demonstrated an influence of the respiratory cycle and, more specifically, rhythmic nasal inspiration for the entrainment of slow oscillations in olfactory cortex during ketamine-xylazine anesthesia. This respiratory entrainment has been suggested to occur more broadly during slow-wave states (including sleep) throughout the forebrain, in particular in the frontal and parahippocampal and hippocampal cortices. Using multisite local field potential recording methods and spectral coherence analysis in the rat, we show here that no such broad forebrain coupling takes place during slow-wave activity patterns under either ketamine-xylazine or urethane anesthesia and, furthermore, that it also does not arise during natural slow-wave sleep. Therefore, respiratory-related oscillatory neural activities are likely limited to primary olfactory structures during slow-wave forebrain states.