Further observations on the spreading depression of activity in the cerebral cortex.

THE spreading depression of activity, a response elicited by local stimulation of the cerebral cortex, has been described previously (4). Briefly, this response consists of a marked, enduring reduction of the “spontaneous” electrical activity, a reduction which appears first at the region stimulated and spreads out from there in all directions, involving successively more and more distant parts of the cerebral cortex. The rate of spread is slow: in rabbits, under dial, a response started in the frontal region takes 4 or 5 minutes to reach the occipital pole. Recovery of the initial pattern of “spontaneous” electrical activity requires 5 to 10 minutes at each region. Specific electrical activity, different from the “spontaneous,” often develops during the period of depression in some cortical regions. This activity, when intense, closely resembles the Qeizure pattern” of experimental epilepsy. The following study considers another aspect of this response: a slow voltage variation, having a duration of several minutes.