ASCENDING CONDUCTION IN RETICULAR ACTIVATING SYSTEM, WITH SPECIAL REFERENCE TO THE DIENCEPHALON

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Abstract
The ascending course of the reticular activating system has been investigated in the brain stem of the cat, with special reference to conduction through the diencephalon. With repetitive stimulation of this system in the bulb or mid-brain, desynchronization of electrical activity has been observed in the sub- and hypothalamus, ventromedial thalamus and internal capsule. Potentials evoked by single shock reticular stimuli are recorded from the same areas. Excitation of these diencephalic regions, in turn, induces generalized desynchronization of electrocortical activity, and single shock stimuli delivered to them evoke widely distributed cortical potentials. These results suggest that alternative routes are available for corticipetal conduction of the reticular activating influence over: (i) a thalamic path involving transmission to the ventromedial part of the thalamus, with relays to the cortex from the remainder of this structure; and (ii) an extrathalamic path involving direct passage into the internal capsule from the sub- and hypothalamus. In agreement, after selective destruction of either one of these routes, leaving the other intact, generalized desynchronization of electrocortical activity could still be elicited by lower brain stem stimulation.

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