It has been observed by neurosurgeons that in a certain number of patients undergoing large craniotomies involving exposure of the brain for long periods and cortical exploration there develop focal symptoms of paralysis, such as hemiplegia and aphasia, even when no cerebral substance has been removed. These symptoms appear within a few hours or one to two days after operation and are generally transitory, although they may persist in some cases for several weeks.
At Dr. Penfield's suggestion, Echlin1 started a series of experiments to determine what effects on the brain or the meninges might be produced by operative exposure. He described lesions following simple exposure of the brain at operation which, from their nature and the similarity of their anatomic distribution to those produced by electrical stimulation, appeared to him to be due to cerebral ischemia. In those animals whose brains were exposed at operation for more than