Local Cortical Activity Of Distant Brain Areas Can Time-Lock To The Respiratory Rhythm In The Freely Behaving Rat
An important unresolved question about neural processing is the mechanism by which distant brain areas coordinate their activities and relate their local processing to global neural events. A potential candidate for the local-global integration are slow rhythms such as respiration, which is also linked to sensory exploration. In this article, we asked if there are modulations of local cortical processing which are time-locked to (peripheral) sensory-motor exploratory rhythms. We studied rats freely behaving on an elevated platform where they would display exploratory and rest behaviors. Concurrent with behavior, we monitored orofacial sampling rhythms (whisking and sniffing) and local field potentials (LFP) from olfactory bulb, dorsal hippocampus, primary motor cortex, primary somatosensory cortex and primary visual cortex. We defined exploration as simultaneous whisking and sniffing above 5 Hz and found that this activity peaked at about 8 Hz. We considered rest as the absence of whisking and sniffing, and in this case, mean respiration occurred at about 3 Hz. We found a consistent shift across all areas toward these rhythm peaks accompanying behavioral state changes. We also found, across areas, that LFP gamma (70-100 Hz) amplitude could phase-lock to the animals respiratory rhythm, a finding indicative of respiration-locked changes in local processing. The respiratory rhythm, although occurring at the same frequencies of hippocampal theta, was not spectrally coherent with it, implying a different oscillator. Our results are consistent with the notion of respiration as a binder or integrator of activity between distant brain regions.