ATTENTION, CONSCIOUSNESS, SLEEP AND WAKEFULNESS 



'573 



mation, and persisted in the absence of auditory cor- 

 tex. 



This important experiment, in agreement with 

 other studies, suggests that the tonic, longer-lasting 

 arousal reaction which is subject to habituation by 

 selective but less differentiated stimuli may be a part 

 of a general arousal and attention mechanism sub- 

 served by the ARAS. With its principal locus in the 

 strategically located reticular formation, capable of 

 monitoring input-output functions, it might be 

 thought of as serving a first order protective, pre- 

 paratory and adjustive function in the manner sug- 

 gested by Cannon, Gellhorn, Hess, Ranson and others. 

 The phasic, shorter-lasting arousal reaction, less 

 susceptible to habituation and capable of greater 

 stimulus differentiation and associated less with ARAS 

 than DTPS, would appear to be mediated by a mech- 

 anism better adapted to the special alerting and highly 

 selective attention needed for higher forms of dis- 

 crimination and learning. 



In the foregoing experiments, as well as in other 

 recent studies (43, 64, 85, 101 103) bearing on 

 arousal, alerting, attention, habituation and condi- 

 tioning, it has become evident that a complex of in- 

 terrelated mechanisms is involved. Specific afferent 

 pathways of communication must be maintained, but 

 it appears necessary also for these to have several 

 points of confluence and convergence within the 

 central nervous system. Specific sensory pathways 

 conduct messages from a variety of specialized and 

 widely dispersed receptors to special destinations in 

 the cortex and elsewhere. Interposed in these path- 

 ways at various strategic locations are relays or syn- 

 apses which are subject to centrifugal influences which 

 regulate and control the sensory influx. 



Attention, perceptual discrimination, conditioning 

 and learning require, however, more than the de- 

 liverance of specific messages to certain segregated 

 locations, for information from several diverse sources 

 must be brought together if elaboration, correlation 

 and integration are to occur. In conditioning, as we 

 know, one sense mode may come to substitute for 

 another in effecting .1 response, and in order to ac- 

 complish this there must be points of confluence and 

 convergence. The reticular formation of the lower 

 brain stem, the unspecific nuclei of the thalamus and 

 the association zones of the cortex appear to be centers 

 of convergence, as does also the hippocampus. These 

 convergence centers, although interposed at different 

 levels of the central nervous system, appear to be 

 mutually interactive and share some functions in com- 



How the separate and conjoined sensory influences 

 in these regions of the brain provide the conditions of 

 discrimination, retention, plasticity and modifiability 

 we know to exist will long be the subject of intensive 

 study, but some progress is being made as the results 

 reported here attest. However, neuroanatomicallv, 

 neurophysiologically and behaviorally, we have barely 

 scratched the surface and much remains to be done. 

 So far in this chapter we have considered mainly the 

 neurophysiological and electrophysiological studies 

 which have revealed new mechanisms and new con- 

 cepts of brain function. We shall now turn to another 

 class of electrophysiological events, the electroenceph- 

 alogram 1 1 . 1 .< . Of more global character it represents 

 ongoing activity in the brain recorded at a distance 

 from the surface of the scalp. 



THE ELECTROENCEPHALOGRAM IN SLEEP 

 AND WAKEFU1 NESS 



Charat Im slu s of the EEG in Wakefulness 



Hans Berger, ;i German neuropsychiatrist, is aptly 

 called the father of electroencephalography. In his 

 first lew articles ( 1 <» 22), he described the basic types 

 of electrical activity generated in the brain of human 

 subjects and recordable from the surface of the scalp. 

 These are described by Walter in Chapter XI of this 



1 1 11 ml hook. 



The normal waking EEG is characterized by a 

 prominent alpha rhythm composed of waves of 8 to 

 1 2 per sec. and about 30 fiY. on the average. The per- 

 sistence, rhythmicity and regularity of the alpha 

 w ,i\ is \ .i! \ hum individual to individual. In a state of 

 quiescence with eyes closed the alpha rhythm is more 

 or less continuous but often shows amplitude modula- 

 tions. Like the ARAS, the alpha rhythm is affected 

 by all types of sensory stimulation. About two fifths 

 (il a second after an unexpected stimulus, the alpha 

 waves block and the EEG may remain in a state of 

 activation with only low-voltage fast or base-line 

 activity for several seconds or longer until the subject 

 has become accustomed to the stimulation. After a 

 lew repetitions of the stimulus the alpha blockade 

 lasts only about 1 sec. before the waves return, and 

 after a number of repetitions habituation may set in 

 with the result that no blocking or suppression of the 

 alpha waves occurs. Visual stimulation is less suscep- 

 tible to habituation than auditory or other types. 



Berger believed the alpha blockade resulted from 

 the focus of attention upon a specific sense mode with 

 generalized inhibition spreading to other sense zones. 



