AN ACTIVATING SYSTEM IN BRAIN STEM OF MONKEY

Abstract

THE EXISTENCE of afferent collateral pathways to areas of the brain stem and diencephalon medial to the well-known long projection systems has been demonstrated anatomically¹and physiologically.²Recently, Starzl, Taylor, and Magoun³have shown in the cat that this centrally oriented core, comprising the midbrain tegmentum, the subthalamus and hypothalamus, and the ventromedial portion of the thalamus, forms a highly integrated system, in the extent of which single shock-evoked potentials of somatic and auditory origin can be recorded from collaterals which leave the median and lateral lemnisci as high as the posterior part of the thalamus. High-frequency stimulation of the peripheral receptors, on the other hand, effected desynchronization of electrical activity in this central core, as well as in the cortex. Furthermore, Moruzzi and Magoun⁴demonstrated that direct high-frequency stimulation of this medial system desynchronized electrocortical activity in a manner exactly paralleling arousal from sleep or