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HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY III 



was located in the experimental room, but they failed 

 to appear if the recording was done elsewhere in the 

 laboratory. The authors were impressed by the 

 durability and persistence of the subcortical rhythms 

 as contrasted to the transitory characteristics of the 

 cortical ones. 



Summary 



Certain generalizations about learning derived from 

 the EEG responses can be made with the reservation 

 that they do not always agree with all the data. At 

 the cortex the CS comes to block alpha waves in a 

 new way that parallels the development of the CR in 

 time. Besides this, the CS can arouse new cortical 

 waves whose existence seems to depend upon the 

 learning process. And finally, the cortical responses 

 evoked by the CS can be larger, more complex and 

 more stable during acquisition and retention than 

 they arc during habituation and extinction. 



But entirely similar electrical changes are also 

 taking place in many other brain locations. Before 

 conditioning, what is to become the CS causes a 

 variable evoked response in the afferent sensory tracts 

 and in limbic Structures; these, like their cortical 

 counterparts, become larger, more complex and more 

 stable in learning. The new cortical waves arc matched 

 bv novel events in limbic and reticular structures 

 that are exactly similar in principle and perhaps even 

 in kind, such waves in the reticular substance may 

 actually be far less fickle and evanescent than the 

 cortical ones. And, finally, the cortical alpha block 

 probably reflects mainly the action of the reticular 

 lui maiion. Thus limbic, reticular and cortical struc- 

 tures arc all involved in learning, if the EEG results 

 an- to be believed. 1 low <>ne can ol ijeciiv elv determine 

 from this evidence alone that one part of the brain 

 is more involved in learning than another is difficult 

 to see. Nor is it possible at the present time to do 

 more than guess at how the three major systems 



cortex, reticular formation and limbic system in- 

 teract with one another. There seems to be little 



question lli.tt lliev do so, ,m<l some interesting funda- 

 mental t.icts will inevitably emerge from experiments 

 ■ In ected at this question. 

 The psychologically, oriented reader will want to 



know how well the EEG (hidings, such as lliev are, 



correlate with the types oi learning recognized in his 

 ■in. II he favors the Pavlovian analysis of con- 

 ditioning he will find Gastaut's summaries (69, 70) 



and thai ol Bu a 8 R |i) informative. In terms 



of the analysis ol learning presented earlier in this 



chapter we can say the following. Type I, Type II 

 and perceptual learning are not yet distinguishable on 

 the basis of their EEG characteristics. Acquisition 

 is accompanied by widespread electrical events, but 

 no single set of them is crucial. A clear case can be 

 made for the involvement of the reticular formation in 

 habituation and extinction; and insofar as attentive 

 functions play a part in learning, the reticular forma- 

 tion is also unquestionably involved. The EEG re- 

 sponses often correlate poorly with the behavioral 

 responses, that is to say, they are not invariably present 

 when the CR appears, nor are they always absent 

 when it does not. A beginning has been made in the 

 study of differential conditioning and of the emotional 

 versus the operant continuum. Taking it all together, 

 EEG correlates have been found for many behavioral 

 manifestations in learning and it is safe to predict 

 that many more will be uncovered when precise 

 modern behavioral control is combined with the 

 electrophysiological method in the study of animal 

 preparations. 



It must be confessed that, from the physiological 

 point of view, the data available art- still scattered, 

 fragmentary and incomplete. The important question 

 of localization of events in different cortical areas, 

 for instance, has been addressed in very few studies, 

 and so long as scalp electrodes are employed, definitive 

 answers probably cannot be expected. This point 

 may be settled bv the implanted microelectrodes 

 just coming into use. 



BRAIN STIMULATION 



Electrical stimulation of the brain of the unanesthe- 

 ti/ed animal combined with a simultaneous measure- 

 ment of behavior is a technique being increasingly 

 employed. In the area of our concerns the objectives 

 are to produce or modify learned behavior bv acti- 

 vating the brain in some artificial order or unnatural 

 degree. Such studies, as we will see, have already 

 developed some interesting information. 



Brum Shocki 'Produce' Bchavim 



While shocks delivered to many brain locations 

 have no elicit whatever upon behavior, at other loca- 

 tions the same shock schedule mav produce dramatic 

 events indeed. Animals that are awake can be put to 



sleep and vice versa; peaceful animals can be made 



to attack viciously, quiet ones become active, and 



autonomic responses like salivation and defd ation are 



