Sleep-like states modulate functional connectivity in the rat olfactory system.

The present study was an examination of state-dependent functional connectivity during spontaneous activity between the piriform cortex and its upstream and downstream connections. Rats were anesthetized with urethan and allowed to spontaneously cycle between fast- and slow-wave states similar to fast- and slow-wave sleep states. Local field potential recordings were made from the olfactory bulb, piriform cortex, dorsal hippocampus, amygdala, and primary visual cortex. The results demonstrate that during slow-wave sleep-like states, when the piriform cortex shows reduced sensitivity to odor input via the olfactory bulb, there is enhanced coherence with other forebrain structures. Granger causality analyses suggest that the link between piriform cortical and hippocampal activity during slow-wave state is in the direction of the hippocampus to the piriform cortex rather than the reverse. The results suggest that slow-wave sleep-like states may provide an opportunity for the transfer and/or consolidation of information related to odor memories, specifically at a time when the piriform cortex is less sensitive to sensory input.