The effects of epileptogenic activity on auditory evoked potentials in cats

Epileptogenic foci were produced by application of penicillin to the auditory cortex of cats. A gradual modification of the evoked potentials to clicks and of the recovery cycle to paired clicks was noted following the application of penicillin. With the onset of interictal spikes, responses were initially depressed. The depression gradually changed till every click triggered a reflex epileptogenic spike. Areas surrounding the primary focus and areas at the mirror focus had depressed evoked potentials, while at the primary focus a click elicited reflex spikes. Progressive recruitment of cortical regions farther away from the primary focus was noted with increased epileptogenicity. The recovery cycle was also affected with prolongation of the absolute refractory period. These complex modifications of sensory input were closely related to the intensity of the epileptogenic disturbance, the distance of the area processing the information from the primary epileptogenic focus, and the time of arrival of the signal to be processed in relation to the interictal and ictal discharges.