Cortico-Spinal Responsiveness During EEG Arousal in the Cat

¹ From the Department of Physiology, University of Oregon Medical School, Portland, Oregon

This study considers the possibility that the greater mobility of the mammal during aroused alertness is due to an elevation of excitability of cortical neurons giving rise to cortico-spinal fibers. Responsiveness of this neuronal population to electrical excitation of the cerebral cortex was measured during periods of spindle bursts in the EEG, during interspindle lulls, and during electrocorticographic arousal initiated by olfactory or by hypothalamic stimulation. Responsiveness during spindle waves varied widely; during interspindle lulls and during induced arousal responsiveness was stable. There were no significant differences between the central tendencies of responsiveness in these three conditions. It is concluded that the unknown cortical mechanisms activated by the change from the comatose to the aroused condition of the EEG do not involve an alteration in the state of corticospinal neurons or their associated cortical interneurons.