Temporal coordination of olfactory cortex sharp-wave activity with up- and down-states in the orbitofrontal cortex during slow-wave sleep

During slow-wave sleep, inter-areal communications via coordinated slow oscillatory activities occur in the large-scale networks of the mammalian neocortex. Because olfactory cortex (OC) areas, which belong to paleocortex, show characteristic sharp-wave activity during slow-wave sleep, we examined whether OC sharp-waves in freely behaving rats occur in temporal coordination with up- and down-states of the orbitofrontal cortex (OFC) slow oscillation. Simultaneous recordings of local field potentials and spike activities in the OC and OFC showed that during the down-state in the OFC, the OC also exhibited down-state with greatly reduced neuronal activity and suppression of sharp-wave generation. OC sharp-waves occurred during two distinct phases of the up-state of the OFC: early phase sharp-waves occurred at the start of up-state shortly after the down-to-up transition in the OFC, while late phase sharp-waves were generated at the end of up-state shortly before the up-to-down transition. Such temporal coordination between neocortical up- and down-states and olfactory system sharp-waves was observed between the prefrontal cortex areas (orbitofrontal cortex and medial prefrontal cortex) and the OC areas (anterior piriform cortex and posterior piriform cortex). These results suggest that during slow-wave sleep, OC and OFC areas communicate preferentially in specific time windows shortly after the down-to-up transition and shortly before the up-to-down transition.

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