'558 



HANDBOOK OF 1'IIYSIOI i >f ; Y 



NEUROPHYSIOLOGY III 



sponding synchronized cortical waves of high voltage, 

 perhaps favoring sleep. It would also seem possible 

 ih.it the slowly rising d.c. pulses might block the 

 influences of the ARAS in maintaining wakefulness, 

 by electrotonic or polarization effects. It has been 

 argued l>\ I less that this is not the case since the same 

 type "I stimulus has been applied in the ergotropic 

 center with excitatory rather than depressive and 

 sleeplike results. 



Nauta's (182) results on sleep in the rat in some 

 respects agree with those of Hess and in other respects 

 are more closely related to the work of Ramon's 

 group. He believes there is a center for sleep in the 

 preoptic and suprachiasmatic regions, and that there 

 exists in the matmnillarv region a center for wake- 

 fulness. According to Xauta the center for wakeful- 

 ness plays a predominant role, and the sleep center 

 of the anterior hypothalamus serves mainly a modula- 

 tory function upon the activity of the center of wake- 

 fulness. 



Origins of the Ascending Reticular Activating 

 System Concept 



Our present knowledge of the ascending reticular 

 activating swrm (ARAS) derives from the discovery 

 by Moruzzi & Magoun (181) that stimulation of the 

 reticular formation of the lower brain stem in the cat 

 produces clectrocortical 'activation 1 or 'desynchroni- 

 zation' and behavioral arousal. This recognition of 

 the ARAS as a second or unspecilk sensory system 

 which plays a very significant role not only in the 

 regulation of sleep and wakefulness, but as a potential 

 integrator of other important functions mediated by 

 the central nervous system has led to some entircK 

 new concepts ol brain function. 



Such an important discovery could scarcely have 

 been made had it not been lor certain antecedent 

 experiments and observations by others. Among 

 these were the pioneering experiments of Berger (19- 

 22) who lirsi successfully described the human elec- 

 troencephalogram in I'l-'f). I lis general findings were 

 confirmed by Adrian & Matthews (6), and subse- 

 quently by a host ol Others. 'See Chapter XI of this 

 Handbook.) His work demonstrated thai the brain has 

 intrinsic rhythms oi its own, among them an 8 to 12 

 per sec alpha rhythm which ma) be blocked l>\ at- 

 tention and sensory stimulation. He showed that 

 waking and sleeping may !»■ distinguished in the 

 IM, b\ their different patterns. I I< l also demon- 

 strated thai conditions which impair consciousness, 



such as anesthesia and epileptic States, produce dis- 

 tinctive lit; change: Each ol these early observa- 



tions was important in its own right, but the funda- 

 mental discovery that the brain has an electrical beat, 

 apart from induced activity, was to prove a tremen- 

 dous stimulus to future work in neurophysiology. 

 Furthermore, the recognition of clectrocortical ac- 

 tivity and its use as an indicator of cortical activation 

 or arousal was exceedingly important in the subse- 

 quent experiments of Bremer (33-35) and Moruzzi 

 & Magoun (181). 



As described in the preceding section, the early 

 concepts of sleep and waking centers were gradually 

 being; revised in the light of the results of stimulation 

 or of lesions made in the diencephalon and brain 

 stem. In this regard the work of Hess (iii, 113, 116) 

 on autonomic centers and the production of sleep 

 by diencephalic stimulation was significant. Perhaps 

 most important of all, since Magoun had been a 

 student of Ranson's and Moruzzi had worked in 

 Bremer's laboratory, were the antecedent experi- 

 ments by these senior investigators. In an excellent 

 review of the experimental work on the hypothala- 

 mus published in 1939, Ranson & Magoun (200) 

 literally anticipated the ARAS concept of a "waking 

 center.' They stated: "In the hypothalamus and 

 particularly in the posterior part of the lateral hypo- 

 thalamus is located a mechanism, which when 

 activated excites the entire organism. Here we have 

 the "waking center". . . . Furthermore, it has been 

 shown that electrical stimulation of the lateral part 

 of the hypothalamus causes a similar generalized 

 somatic and visceral activation, and, when applied 

 in an unanesthetized cat which has been lying quietly 

 on its side with eyes closed, causes it 10 become alert, 

 wide awake and intensely excited." 



Alter commenting that the foregoing reaction was 

 due to descending influences, they pointed out: '"It 

 is probable that the active hypothalamus not only 

 discharges downward through the brain stem, spinal 

 cord and peripheral nervous system into the body but 

 also upward into the thalamus and cerebral cortex." 

 These remarks indicate that there was a growing 

 awareness of the importance of the caudal portion 



of the hypothalamus (and elsewhere, the rostral 



mesencephalon) not only as a 'waking center,' but 

 one capable of arousing and alerting the entire 

 organism. 



Bremer 1 ■;■; 35) was the first to demonstrate by 



elernocortic.il and behavioral methods that a mid- 

 brain transection in the cat, his now famous cerveau 

 isoli preparation, produced characteristic signs of 

 profound somnolence, lie attributed the sleep thus 



produced to a generalized deafferentation which .11 



the time, prior tO know ledge ol I he role of the ARAS 



