ATTENTION, CONSCIOUSNESS, SLEEP AND WAKEFULNESS 



!5 8 9 



a state, he recognizes that in normal sleep or awaken- 

 ing from sleep a suggestion is not reacted upon unless 

 the proper 'set' has been established. He finds a 

 similar thing in hypnosis, that a readiness and will- 

 ingness to respond as the hypnotist directs is a factor 

 in the effectiveness of suggestion. This would seem to 

 imply some kind of plane of reduction, since the sub- 

 ject would not necessarily assume this set under nor- 

 mal conditions. Further careful study is needed of 

 hypnotic influences if the neural mechanism of this 

 remarkable condition is to be understood. Presumably 

 much of this will have to be done with the EEG as the 

 principal liaison between modern neurophysiological 

 conception and the hypothetical states of hypnosis. 



SUMMARY 



A cursory review of the history of concepts con- 

 cerning sleep and wakefulness centers in the brain 

 has been attempted with impressions of the steps 

 which have led to the modern concept of wakefulness 

 as dependent upon the reticular system. Several 

 sources of stimulation which influence the reticular 

 formation in the lower brain stem and, through it, 

 the ascending reticular activating sv stein (ARAS) art- 

 discussed. The ARAS influences the cerebral cortex 

 and higher brain centers diffusely, lint may also have 

 more differentiated effects, some of which may act 

 through the diffuse thalamic projection astern 

 (DTPS) in such a manner as to regulate cortical 

 activity and excitability, especially in associational 

 fields. In addition to this nonspecific influence the 

 ARAS and DTPS may act differentially with respect 

 to the fields of reception served by the specific tha- 

 lamic projection systems (STPS). 



Wakefulness is maintained by excitation of the 

 reticular formation and the ARAS through collaterals 

 from all sensory pathways, by corticifugal impulses 

 originating in various regions of the cortex and by 

 humoral factors which affect particularly the rostral 

 portions of the reticular formation. Increased activity 

 in the ARAS through .my of these sources of excita- 



tion acts upon the cortex by changing the pattern of 

 its electrical activity from the slow waves and spindle 

 bursts of sleep, or the alpha waves of relaxed wake- 

 fulness, to a pattern of low-voltage fast waves, com- 

 monly referred to as 'activation.' Electrocortical ac- 

 tivation is accompanied by behavioral arousal and 

 by alertness and attention. 



The elusive term 'consciousness' has been consid- 

 ered as a graded form of awareness, ranging from the 

 simplest perceptual discriminations to the more com- 

 plex cognitive forms of abstraction and thinking. It 

 has no precise locus on the sleep-wakefulness contin- 

 uum described in terms of EEG patterns, behav- 

 ioral characteristics and states of awareness. Uncon- 

 sciousness in which perceptual contact with the 

 environment is lost can be identified roughly with the 

 onset of sleep in Stage C of the EEG in which delta 

 waves and 14-per-sec. spindle bursts predominate. 

 Other forms of unconsciousness induced by breathing 

 low oxygen mixtures, by hyperventilation, by insulin 

 coma, by deep alcoholic intoxication and by some 

 seizure states are maink associated with the onset and 

 persistence of large ami slow waves. In grand mal sei- 

 zures and in some physiological, drug and anesthetic 

 conditions, loss of consciousness is associated with 

 high-voltage fast activity. 



Attention is closely allied to arousal and wakeful- 

 ness and, like wakefulness and consciousness, appears 

 to be a graded phenomenon extending from general 

 alerting, .is in the orienting reflex, to specific alerting, 

 as when attention is focused upon a given sense mode 

 and dominates sensory input to the point of exclusion 

 of other sense modes. Still higher or more finely 

 focused attention m.iv lie restricted to a limited aspect 

 of a given sense mode. 



Recent neurophysiological findings have been con- 

 sidered which not only broaden the scope of modern 

 concepts of brain organization and function, but bear 

 specifically upon the mechanisms which may underlie 

 and subserve the processes of attention, perception 

 and learning. 



REFERENCES 



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