Rhythmic electrical activity from isolated cerebral cortex

Bremer has demonstrated that rhythmic activity of the cerebral cortex, similar to the alpha rhythm, represents an inherent property of the cortex itself. In spite of Bremer's findings there has been considerable disagreement as to whether the rhythmic cortical activity depends upon the interaction of the cortex and subcortical structures, or whether the cortex is able to produce spontaneous rhythms. Spontaneous and induced cortical activity has been investigated in cats in intact hemispheres, in hemispheres after thalamectomy, and in portions of the cortex which have been completely isolated from the rest of the brain. Both after thalamectomy and after severance of all subcortical and intracortical connections to a small portion of the cortex, spontaneous rhythmic cortical activity was recorded, resembling the normal alpha rhythm. Electrical activity induced by electrical or chemical stimulation in such preparations was indistinguishable from activity induced by the same means in normal hemispheres. The results of this study give support to Bremer's views on the origin of the rhythmic cortical activity, and have led to the following conclusions: 1. 1. Rhythmic electrical activity, closely related to the alpha rhythm, is an inherent property of the cortex itself. It is not necessarily dependent upon thalamo-cortical circuits, though these circuits, when present, may modify its form and amplitude. 2. 2. The explanation of contradictory results obtained by some authors may be due to conditions of the cortex following operative procedures. The facility with which the effect of such procedures can be reversed by chemical stimulants like eserine and acetylcholine should be emphasized. 3. 3. Rhythmic electrical activity in response to electrical or chemical stimulation of the cortex has the same characteristics in an isolated portion of the cortex as in normal cortex with intact connections, under the conditions of our experiments.