FURTHER OBSERVATIONS ON THE SPREADING DEPRESSION OF ACTIVITY IN THE CEREBRAL CORTEX

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Abstract
A slow voltage variation having a duration of 4-6 min. accompanies the spreading depression of activity in the rabbit''s cerebral cortex which has previously been described. Each cortical region first becomes negative with respect to an extracortical reference electrode, for 1-2 min. This negativity reaches, within 0.5-1 min. a maximum of 8-15 mV and then decreases somewhat more rapidly. The region then becomes positive for 3-5 min., this phase having usually a smaller amplitude than the negative. A sudden cortical anemia, resulting from a 1-min. arterial occlusion, abolishes the "spontaneous" electrical activity of the cortex without itself inducing a slow voltage variation, but it promptly and profoundly alters the slow voltage variation accompanying the spreading depression of activity. This alteration consists essentially of a prolongation and an increase of the negativity. In a cortex, in no part of which a spreading depression of activity is in progress at the time, interruption of the circulation for longer periods induces a slow voltage variation only 2.5-5 min. after the arterial occlusion, at which time the cortex becomes negative. The cortex then remains negative for as long as the circulation is interrupted (up to at least 12 min.). The results seem to indicate that in the spreading depression of activity, a change of the same nature as one resulting from prolonged interruption of the circulation, occurs in the cerebral cortex. The electrical sign of this change is the negative voltage variation.

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