Conduction of Cortical Impulses to the Autonomic System

Abstract

Clinical as well as experimental observations show that the cortical centers of vegetative organs are, in many instances, in close topical relation to those of adjacent skeletal muscles. The descending corticofugal tracts to the peripheral part of the autonomic system are topographically related to the pyramidal tract. They also lose their excitability after destruction of the motor cortex and frontal lobe, within the same time as do the corticofugal somatic fibers. (Spiegel, 1 Friedberg. 2 ) It seemed, therefore, of interest to ascertain whether the pyramidal tracts by themselves can conduct corticofugal impulses to the autonomic system. The experiments were performed on 30 cats. In a first series, the “extrapyramidal” fibers that arise from the hypothalamus were severed by deep incision into the floor of the 4th ventricle. The central grey matter and tegmentum in the pons and midbrain were destroyed where the centrifugal fibers of the hypothalamus are located. In a second series of experiments, the conduction of cortical impulses to vegetative organs was studied after transverse section of both pyramidal tracts on the base of the pons. After the lesion of either of these systems had been performed, the effects of stimulation of the motor cortex and the frontal lobe was noticed on the pupil, the blood vessels, the heart, the sweat glands and the urinary bladder.

In the study of the pupil, the lesion of the brain stem was combined with unilateral cervical sympathectomy. Thus, cortical stimulation elicited on the pupil ipsi-lateral to the sympathectomy only inhibition of the sphincter, on the other pupil inhibition of the oculomotor plus stimulation of the sympathetic.