EPICORTICAL SLOW POTENTIAL SHIFTS AND SENSORY-EVOKED POTENTIALS ARE RELATED TO SEIZURE PROPENSITY IN GERBILS

Gerbils were assessed for behavioural tendency by scoring seizure seve rity and the amount of ambulatory and rearing activities in a novel 'o pen-field' arena. Seizure-prone animals exhibited seizures on early op en-field trials (1-2) and later performed more ambulatory activity tha n non-seizure-prone animals. Two weeks later, two groups of both seizu re prone and non-seizure prone animals were chronically implanted with six silver/silver chloride ball electrodes for recordings during beha viour. Electrodes were on the surfaces of the frontal, parietal and oc cipital cortices bilaterally. In one group these were used to record s low potential shifts; in the other, visual- and acoustic-evoked respon ses. Larger negative and positive slow shifts occurred in seizure-pron e animals. Most evident were the larger positive right frontal shifts and negative left occipital shifts. Seizure tendency was related to th e amplitude of these waveforms. Visual-evoked potential amplitudes wer e generally larger and latencies shorter in seizure-prone animals, esp ecially in the right occipital and left parietal cortices. Seizure sus ceptibility was associated with increased visual-evoked potential ampl itude in the right frontal and left occipital cortices, and with reduc ed latency of both auditory-and visual-evoked responses in the left oc cipital cortex. The discussion highlights a role for glia in slow shif t generation and the association of large shifts with enhanced sensory -evoked responses, especially in seizure-prone animals.