Electrical Activity of the Cerebral Cortex as Compared to the Action Potential of Excised Nerve

Abstract

As Bartley and Newman have shown, there can be recorded from the cerebral cortex, over considerable of its surface, a continuous and extremely complicated series of electrical oscillations. The record as it appears on the cathode ray oscillograph, with adequate sensitivity to show its complexity, is far too intricate for any such casual analysis into specific waves as is possible in nerve trunks.

That this activity consists of a complication of more simple elements is indicated by the following experiments: If in the rabbit's or dog's cortex shallow cuts (1 mm. deep) are made near a recording electrode (an indifferent electrode being located on the bone of the skull), the form of the record changes, becoming simpler. Cutting off the blood supply from an area causes its activity to cease in 5 to 10 minutes, without any obvious simplification. Ether anesthesia may cause marked simplification of the record at a stage shortly before all activity ceases. The simplest large waves have a duration of 30 to 100 sigma, but in the complex picture there appear to be some as short as 10 sigma. The amplitude of individual waves of the normal record may be as much as 1/2 mv. increasing upon stimulation of the animal to several times this. No oscillations can be found even at a sensitivity of 1/2 meter per mv., that have as short a duration as nerve-fiber action potentials. The long refractory period, low frequency, long duration and suppression by anesthesia at a concentration that does not affect nerve fibers indicate that nerve cells spontaneously active in the cortex are involved, and suggest that the potentials themselves may be cell potentials rather than nerve-fiber potentials. Further, responses to direct electrical stimuli are too long in duration for nerve-fiber potentials, and are of the order of duration of the spontaneous waves.