Influence of cortical steady potential on evoked potentials and neuron activity

Abstract

Previous experiments had suggested that the relationship between neuron activity and the evoked potential produced by light flashes in the cat's visual cortex is influenced by the cortical steady potential. This observation has now been quantified by measuring the area enclosed by the slow late components of the evoked potential. These measurements showed that the area of the slow negative wave increase linearly as the steady potential became less negative, while the area of the slow positive wave decreased linearly. There also appeared to be a linear relationship between cortical neuron activity during the slow negative wave and the area of this wave, neuron firing decreasing as the slow negative wave became larger. On the other hand, there was no correlation between neuron firing during the slow positive wave and the area of this wave. It was further shown that steady potential shifts due to changes in pCO 2, whether produced by hyperventilation or occurring spontaneously, are not associated with any consistent changes in the pattern of neuron activity or of the evoked potential. Thus, a definite correlation between the cortical steady potential and neuron activity in the visual cortex of cat encéphale isolé preparations exists, but only if non-neuronal factors that can influence DC recordings are held constant.