The role of the pyriform cortex in the generation of interictal spikes in the kindled preparation

The development of interictal spikes (IIS) was monitored during amygdala or pyriform cortex kindling in a series of 4 experiments. It was found that (1) spike-like transients were often present in the pyriform cortex EEG before kindling had begun; (2) these transients developed progressively into large amplitude and complex IIS as kindling proceeded; (3) the pyriform cortex IIS continued to show the greatest proportion of earliest onset spikes in most animals after kindling was completed; (4) other sites (including the ventral, but not the dorsal hippocampus) gradually developed the capacity to generate IIS as kindling progressed; (5) although specific sites within the pyriform cortex may serve as a generator, their location along the longitudinal axis of the pyriform lobe varied from animal to animal (and did not appear to depend upon the location of the kindling electrode); (6) although there often appeared to be 2 spike types, based on the polarity of the first component, there were also transitional waveforms, raising the possibility that they were variations on a single spike type, and (7) the IIS were often preceded, usually in the pyriform cortex, by reliable pre-spike events (smaller spikes or a 'ripple' on the EEG).