Epicortical slow potential shifts and sensory-evoked potentials are related to seizure propensity in gerbils

Gerbils were assessed for behavioral tendency by scoring seizure severity and the amount of ambulatory and rearing activities in a novel 'open-field' arena. Seizure-prone animals exhibited seizures on early open-field trials (1-2) and later performed more ambulatory activity than non-seizure-prone animals. Two weeks later, two groups of both seizure prone and non-seizure prone animals were chronically implanted with six silver/silver chloride ball electrodes for recordings during behaviour. Electrodes were on the surfaces of the frontal, parietal and occipital cortices bilaterally. In one group these were used to record slow potential shifts; in the other, visual- and acoustic-evoked responses. Larger negative and positive slow shifts occurred in seizure-prone animals. Most evident were the larger positive right frontal shifts and negative left occipital shifts. Seizure tendency was related to the amplitude of these waveforms. Visual-evoked potential amplitudes were generally larger and latencies shorter in seizure-prone animals, especially in the right occipital and left parietal cortices. Seizure susceptibility was associated with increased visual-evoked potential amplitude in the right frontal and left occipital cortices, and with reduced latency of both auditory- and visual-evoked responses in the left occipital cortex. The discussion highlights a role for glia in slow shift generation and the association of large shifts with enhanced sensory-evoked responses, especially in seizure-prone animals.