Ascending Conduction in Reticular Activating System, With Special Reference to the Diencephalon

Abstract

RECENT study has revealed a cephalically directed brain stem system whose stimulation desynchronizes the electrical activity of the cerebral cortex in a manner simulating that observed in awakening from sleep or in the EEG arousal reaction (8). This system was found to be distributed in the reticular formation of the medulla, the tegmentum of the pons and midbrain and the sub-and hypothalamus. The means by which its activating influence became exerted upon the cortex was speculated upon and, because of the generalized distribution of the cortical effects, it seemed likely that the diffuse thalamic projection system was concerned. Some evidence favoring this possibility was obtained but the problem was left for further investigation.Following preliminary determination of the organization of the diffuse thalamic projection system (12), the present study has explored this matter further: (i) by determining the thalamic regions whose electrical activity is desynchronized by stimulation of the reticular formation of the lower brain stem, (ii) by determining the distribution of thalarnic sites from which evoked potentials are recorded upon single shock stimuli to the reticular activating system, (iii) by exploring the thalamic areas whose direct excitation desynchronizes the electrocorticogram, (iv) by ascertaining the distribution of cortical potentials evoked by single shock stimulation of the reticular activating system, and (v) by determining the effect of diencephalic lesions on ascending conduction of the reticular influence. The results indicate that the ventromedial part of the thalamus is most critically involved in transmission of the reticular activating influence, with the rest of the thalamus (including the diffuse thalamic projection system) playing a subsidiary role. Evidence, moreover, is provided that a proportion of the influence of the reticular activating system upon the cortex may be exerted by an extra-thalamic route, paralleling that of the secondary response system described by Morison et al, (1, 10, 11). METHODSCats immobilized with B-erythroidine were used, with a Palmer respirator providing artificial respiration. Exposures were made under local procaine. S m d doses of chloralo---

Collateral Afferent Excitation of Reticular Formation of Brain Stem

“…The regions outlined in the present study are also those through which the EEG arousal reaction is mediated, judged both from direct stimulation and recording techniques (19). I t is well \known that the cortex is widely activated by afferent stimuli, although the -direct sensory path goes only to a discrete cortical area.…”

“…The ascending course of this reticular activating system is distinct from that of afferent pathways in the brain stem (19) and selective destruction of its cephalic portion is followed by the EEG synchrony and behavioral somnolence, hitherto attributed to deafferentation of the cerebrum (7, 8). Such consequences do not follow selective interruption of ascending somatic and auditory paths in the midbrain and after this latter injury both somatic .…”

A modern Cosmas and Damian: Sir Roy Calne and Thomas Starzl receive the 2012 Lasker~Debakey Clinical Medical Research Award

“…Proposing the impossible Thomas Starzl entered medical school at Northwestern University in 1947. After three years of medical school, he took a year off to do research with Horace Magoun, studying the processing of sensory stimuli by the reticular formation (8)(9)(10)(11)(12). His work in Magoun's laboratory earned Starzl a Ph.D. in neurophysiology and an M.A.…”

Diffuse Thalamic Projection System in Monkey

“…In a dozing animal, such high frequency sensory stimulation obliterates all background synchrony in these nuclei, paralleling a ubiquitous cortical desynchronization (34). This generalized electrical arousal is now known to occur largely through the reticular activating or sensory collateral system (20,25,34,35) which includes at i1,s rostra1 pole the diffuse nuclei. It seems reasonable from this that these nuclei play a part, through their projections, in the mediation of this effect.…”

“…It seems reasonable from this that these nuclei play a part, through their projections, in the mediation of this effect. Although undoubtedly the case, it has also been shown (35) that the role of these nuclei in cortical arousal, while perhaps important, is not critical.…”