Patterns of cortical population discharges during metrazol-induced seizures in cats

Abstract

1. 1. Discharges of neuronal populations were recorded, together with the electrocorticogram (ECoG), in various areas of the cortex and in the pyramidal tract simultaneously, throughout Metrazol-induced seizures in curarized cats. Quantitative evaluation of the level of neuronal discharge was deduced from sequential numbering of multi-unit spikes recorded during the course of a seizure. 2. 2. The organization of cortical cell discharges during Metrazol-induced seizures presented a constant pattern in which three stages could be distinguished: (a) initial paroxysmal bursts at increasing level; (b) tonic discharge maintained for a few seconds at maximal level; (c) clonic bursts of high level recurring until the abrupt end of the seizure. 3. 3. The convulsive discharges of pyramidal tract fibres followed the same pattern. They were similar to and synchronous with those of motor cortex neurones. It was therefore assumed that the population explored in the motor cortex consisted mostly of pyramidal cells. 4. 4. The same general pattern of neuronal ictal discharges was found in the different cortical areas examined, with high variability in occurrence and accuracy of synchronization. 5. 5. The relationship between convulsive ECoG waves and neuronal activity varied according to whether the discharge was phasic or tonic in character. During the first and the third stages of the seizure a clear correlation appeared between the paroxysmal bursts and surface-positive waves. Interruption of cell discharges during surface-negative waves was less constant. Tonic discharges bore no clear relation to the concomitant ECoG waves.