Electrocorticographic activity of the prepyriform cortex during the sleep-wakefulness cycle of the freely-behaving rat.

The electrocorticographic (ECoG) behavior of prepyriform cortex (PPC) was studied during the spontaneous sleep-wakefulness cycle (SWC) of freely-behaving rats in which recording electrodes had been chronically implanted in PPC, neocortex (NEO), entorhinal area, olfactory bulb (OB), hippocampus, and dorsal neck muscles. The different phases of the SWC were discerned by taking into account the NEO, OB and neck musculature electrical activities, and criteria were set for the identification of various PPC ECoG patterns. The existence of rather regular associations between the PPC ECoG and the various SWC phases was demonstrated, but it was also seen that these associations defied simplistic generalizations. Thus, whereas the level of ECoG activity (in terms of synchronization vs. desynchronization) was, in the majority of instances, equivalent in PPC and NEO in some SWC phases (alert wakefulness, synchronized sleep and paradoxical sleep), the same was not true in the case of the relaxed wakefulness, drowsiness, intermediary and preparadoxical phases. In the same context, when the time relationships between the alternations of different SWC phases and PPC ECoG patterns were analyzed, it became clear that although only rarely the PPC transition occurred after the correspondent SWC one, the former could either precede, or be simultaneous with the latter, depending on the particular SWC transition being considered. The neural control mechanisms possibly responsible for the coupling of PPC and NEo EcoG activities are briefly discussed.