FUNCTIONAL ALTERATIONS IN MOTOR AND SUPRANUCLEAR MECHANISMS IN EXPERIMENTAL CONCUSSION

Abstract

Concussion was produced by applying adequate force to the cat''s brain by means of a pendulum striking the head or an hydraulic system connected with the interior of the cranium. Respiration ceased; the canthus, pupillary-light, startle and pinna reflexes disappeared; the pupils dilated and the nictitating membrane retracted. Electrical stimulation within the brain by means of fine electrodes placed with the Horsley-Clarke instrument revealed that excitability of the intra- and extra-cranial portions of the cranial motor nerves and of the descending fibers from the cerebral cortex in the basis pedunculi were unimpaired in concussion. Excitability of nerve-cell groups comprising cranial motor nuclei was impaired less frequently, to a smaller degree and for shorter intervals than excitability of supranuclear motor parts, such as brain-stem tegmentum, hypothalamus and motor cortex. The inspiratory center of the medulla oblongata behaved much like a cranial motor nucleus. Cessation of respiration and abolition of reflexes appeared not to be motor defects. Concussional alterations in function set in at the moment concussion was produced and functional recovery occurred gradually. A brief, often momentary, excitatory effect on motor neurons, apparently correlated with decreased thresholds, was sometimes observed upon concussion.