Propagation of epileptiform potentials in the guinea-pig piriform cortex is sustained by associative fibres

The role of the associative connections in the propagation of epileptiform discharges originating from an acute, localized epileptic focus in the anterior piriform cortex has been characterized recently in the in vitro isolated guinea-pig brain preparation. The present study demonstrates that the dorsal propagation of epileptiform synaptic potentials generated in APC is carried by long-projective associative fibres. Current source density analysis of the field potential profiles evoked by stimulation of the lateral olfactory tract has been utilized to describe the functional circuit activated in rostral and caudal regions of the piriform cortex, before and after the induction of a bicuculline epileptic focus in the anterior piriform cortex. Separate stimulation of the lateral olfactory tract at two sites, caudal and rostral to a tract incision, activates epileptiform potentials that are generated at the site of primary focus in the anterior piriform cortex and travel along associative fibres. Selective cutting of the long-projective associative fibres abolishes the epileptic associative potential in the cortical regions caudal to the section. The present study demonstrates directly that epileptiform potentials propagate along associative fibres to cortical regions that are synaptically related to the focus of origin. Such a pattern of propagation may sustain the generation of secondary foci in cortical regions remote from the primary epileptic focus.