Evoked and spontaneous extracellular potassium shifts in the cerebral cortex of unanaesthetized cats.

Ion sensitive potassium selective double barrel micropipettes were used to measure simultaneously the changes in extracellular potassium and extracellular field potentials at identical locations in the cerebral cortex of head restrained cats. Field potential changes were evoked by direct electrical cortical stimulation, by electrical stimulation of the mesencephalic reticular formation, by painful cutaneous shock and by presenting meaningful stimuli like food. Field potential changes that may occur during the spontaneous oscillations of alertness were also recorded. The surface negative field potentials evoked by electrical stimulation of the cortex, mesencephalic reticular formation or by painful cutaneous shock were accompanied by marked extracellular potassium increases. Conspicuously large potassium increases (nearing the 10 mM levels) accompanied the "event-related" potentials elicited by meaningful stimuli, while no consistent relationship could be observed between the changes of extracellular field potential and potassium. Compared to these events, minor extracellular potassium shifts were seen during the spontaneous oscillations of alertness, although marked potassium increases could be observed in the absence of any provoking stimuli as well. It is suggested that both neuronal and glial elements are involved in the genesis of slow cortical potentials.