Spread of epileptiform potentials in the neocortical slice: recordings with voltage-sensitive dyes

The spread of epileptiform potentials in guinea pig neocortical slices was investigated by use of voltage sensitive dyes and a fast optical recording technique. Epileptiform activity was induced in a perfusion medium containing 10-20 microM bicuculline-methiodide and by single pulse stimulation of layer I or the white matter. The location of minimal and maximal amplitudes, the shape of the potentials at specific sites and the velocity of spread were independent from the specific stimulation site. The expression of epileptiform activity appeared to depend on specific, possibly geometrical, properties of the tissue.