Intracortical synchronization of epileptic discharges at different stages of ultrastructural rearrangements in a completely neuronally isolated area of rat neocortex.

Cross-correlation functions were used to study the time delay (a measure of synchronization) in the appearance of epileptic discharges in distant areas of the cortex in the intact cortex and in neuronally isolated cortical strips in Wistar rats. Experiments were performed at different stages of axon sprouting 30 and 90 days after isolation of cortical areas and in intact cortex. Significant increases in the number of synapses in layer V of isolated cortical strips at 30 days correlated with significant decreases in the time delay, while decreases in the number of synapses at 90 days correlated with a significant increase in the time delay. This is evidence that newly formed synapses increase the extent of synchronization and thus affect epileptogenesis. The data obtained here suggest that large pyramidal cells in layer V of the rat neocortex form a neural network in pathological conditions, this supporting intracortical synchronization of epileptic discharges.