Electrical Activity of Isolated Cortex in the Unanesthetized Cat with Intact Brain Stem.

Summary. 1. The electrical activity of isolated parietal cortex in the un‐anesthetized cat with intact brain stem has been analyzed. The data confirm that neuronally completely isolated cortex with preserved blood supply has the capacity of generating rhythmic electrical activity. 2. Electrical activity appeared spontaneously in the isolated areas, a fact confirming other studies with similar preparations. The spontaneous activity could be reversibly blocked by small doses of barbiturates. Brain stem mechanisms which were intact may have increased the excitability of the isolated area through extraneuronal means. The excitable slab becomes electrically active — it is assumed — due to the ‘stimulating’ influence of circulatory and/or humoral factors in the cortex. 3. The paroxysmal bursts, recorded from isolated cortex, showed a strong resemblance to a similar activity reported by other workers. A slow wave component of the bursts was found to be dominated by 2.5 to 3.5 per second waves of high voltage which often attained very regular characteristics. 3 per second sinusoidal forms as well as 3 per second spike and wave forms were often recorded. In the EEG record these rhythms appeared synchronous over the isolated area. The data demonstrate that the cortex itself possesses the inherent mechanisms necessary for the production of a 3 per second pattern similar to the one met with in petit mal epilepsy. Some conditions for the appearance of such a pattern in isolated cortex are discussed. 4. Apart from the 3 per second rhythms and a fast frequency component (of frequencies of up to 65 c/s), the slab activity was highly irregular, demonstrating a variety of frequencies and wave forms seen in the routine EEG. The data seem consistent with the view that the regulation and maintenance of the alpha rhythm, as well as other regular cortical patterns, are based upon an inter action between the cortex and other neuronaI structures (cortical as well as subcortical). 5. It is emphasized that not only purely interneuronal relationships, but also circulatory conditions as well as other factors — as yet unknown — may determine the form and frequency of rhythmic electrical events of the cortex.