Surface anodal direct current was applied to the motor cortex at the respresentation of the contralateral forelimb in anesthetized or unanesthetized rabbits. The first abnormal activity (isolated spikes) appeared as the current intensity reached ca. 100 μA. The activity occurred first from the frontal pole in most cases. As the current was further intensified, spikes became more frequent. Sharp waves, augmented fast waves and slow waves were also included in the seizure activity. Finally, all the cortical leads were involved in serious seizure activity, which was highly disordered and looked like noise. However, the author believed that this highly disordered EEG activity was not an artifact, but rather electrocortical activity because of the following reasons: 1. Sometimes, a seizure with a similar pattern occurred after the polarizing current was turned off. 2. Seizure activity started mostly from the frontal pole, which was rather distant from the polarizing anode. 3. Multiple unit discharges were recorded from the cortex under the polarizing electrode only during serious seizure activity. 4. Augmentation of microvibration at the distal end of the forelimbs was observed in parallel with seizure activity.
No apparent movement, except for augmented microvibration of the forelimbs, was observed even during serious cortical seizure activity. Therefore, cortical efferent neurons probably cortributed little to the seizure activity. Intense surface anodal current, which is sufficient to induce seizure EEG activity may have a strong facilitatory effect on certain types of cortical neurons, as indicated by the intense neuronal discharges recorded during seizure EEG activity.
