SPREADING DEPRESSION OF ACTIVITY IN THE CEREBRAL CORTEX

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Abstract
In rabbits, under dial narcosis, weak stimulation of the exposed cerebral cortex is followed by a depression of the spontaneous electrical activity. The depression then slowly spreads in all directions. Within 3-6 mins. it involves all of the dorso-lateral cortex except area retrosplenialis granularis dorsalis (Rsg [beta]) of Rose. The depression is more readily initiated in the frontal than in the occipital areas. Recovery requires, as a rule 5-10 mins. at each region. Recovery is often well advanced at the stimulated region when the depression is just starting in distant parts. Only with supraminimal stimulation does the depression spread to the opposite hemisphere, then appearing first in the region symmetrical to the point of stimulation. The spreading depression involves the cortical responses to touch, to electrical stimulation of afferent nerves, to illumination of the retina, to ipsilateral or contralateral cortical stimulation (electrical) and to local application of strychnine or of eserine plus acetylcholine. Single shocks applied to a depressed region fail to elicit typical responses in the opposite non-depressed hemisphere. Large, slow, localized potential waves, during which one electrode becomes negative with respect to others 1-3 mm. distant, often develop during the period of depression. Fast components may also appear. The activity, when intense, closely resembles the "seizure pattern" of exptl. epilepsy. The spread of "tonic-clonic" responses is probably mediated by the same cortical elements which mediate the spread of depression. The two processes require little or no contribution from sub-cortical centers.

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