[Analysis of prolonged evoked potentials of the cerebral cortex]

Evoked responses of the motor cortex (dendritic and slow negative potentials) elicited by its direct electrical stimulation, primary, nonspecific and antidromic responses elicited by stimulation of ventrolateral and intralaminar thalamic nuclei and pyramidal pathways and the respective postsynaptic responses of neurons were studied in acute experiments on curarized cats. The potentials evoked during direct cortical stimulation, as well as during stimulation of specific and nonspecific thalamic nuclei and pyramidal pathways were recorded from one and the same point of the motor cortex, while the respective intracellular responses--from one and the same neuron. It is demonstrated that slow negative potentials evoked under these stimulation conditions and the corresponding IPSP follow an identical time-course. The results obtained indicate that the slow negative potential is the reflection of hyperpolarization of pyramidal neurons. The individual components of various evoked potentials recorded from the cortical surface are supposed to be of common genesis.