'47-' 



IIWDHiiiiK OF PHYSIOLOGY " NEUROPHYSIOLOGY III 



relevant data abound in profusion, these often do not 

 fit together in an orderly pattern, and they sometimes 

 raise more questions than they answer. Besides this, the 

 available methods for studying learning are frequently 

 inadequate, and the ones best suited to the task have 

 not been in use long enough to fulfill their promise. 

 We will therefore be able to provide only a partial 

 description of the mechanisms, this being derived 

 from a statement of the problems as we see them, a 

 summary of the data obtained by various methods and 

 a discussion of some of the possible ways in which the 

 nervous svstem functions in learning. 



The study of the neural basis of learning is inter- 

 disciplinary; it draws on the facts and methods of a 

 number of different fields. Experimental psychology, 

 the discipline most directly charged with precisely 

 defining the behavior called learning and con- 

 ditioning, has made a substantial contribution, and 

 familiarity with its techniques and terminology is 

 required for any serious student of learning. For this 

 reason, we devote the next section to 'Psychological 

 Methods and Terms.' The several biological sciences, 

 and particularly neuroanatomy, neurophysiology and 

 biochemistry, arc also heavily represented in the work 

 on learning. What they offer in the way of methods 

 and facts at the present time appears in the sections 

 'Ablation Studies,' 'EEG Correlates,' 'Brain Stimu- 

 lation' and 'Psychopharmacology.' From a study of 

 this material, the reader will lie prepared, we trust, 

 lor the theoretical explanations for learning that are 

 treated in the final sections. 



But first .1 word about the references. Material 

 published alter June i<)")7 has not been cited with .1 

 lew notable exceptions. The selected list here w.is 

 chosen furthermore so that the reader could, by con- 

 sulting their bibliographies, uncover practically every- 

 thing known about the problem. We feel fairly certain 

 of this with respect to the western literature despite 



the absence ol .1 single modern German citation. I he 

 Russian . 1 1 11 1 eastern European literature is another 

 m. iin 1 I he language diffi< ulty here has been formi- 

 dable, and we have worked either from brief summa- 

 ries of obviously large research programs under way 

 for many years, or from the translation <>l as few as 



One paper in .1 much larger series bv the same author, 



Besides this, out Eastern colleagues in mam instances 

 approai h learning problems in an interestingly diffei 



enl way 1 our own, and we are not entirely sure 



that, as reporters, out rendering of their facts and 

 elusions his always been wholly accurate. 



Certainly our report is not complete, much as we 

 would have liked it to be. 1 



PSYCHOLOGICAL METHODS AM) TERMS 



Although philosophers and scientists have long 

 speculated about the nature of learning and have 

 observed it in pets, zoo animals, children and fellow 

 men, the first systematic observations of learning and 

 memory were made by Ebbinghaus in i88~, (551. With 

 nonsense syllables, which he invented, he carefully 

 measured the course of memorizing and forgetting in 

 human subjects. Then in 1906 Pavlov described (in 

 English) his now famous discovery of the conditioned 

 reflex, describing various factors governing its acqui- 

 sition and extinction (180). About the same time, the 

 maze was first employed for the measurement of 

 learning in animals (221); and the problem box, in 

 which an animal must discover through trial and 

 error the solution to a problem, was used for a similar 

 purpose (235). Thus were launched the two general 

 kinds of methods, the conditioning method and the 

 trial-and-error method, which have since provided 

 the great bulk of information about learning and the 

 various factors that affect it. It is necessary to have a 

 clear understanding of these psychological techniques 

 and the terminology that goes with them before 

 turning to the neural correlates of learning and con- 

 ditioning. 



Conditioning 



As Pavlov used the term, 'conditioning' applied to a 

 situation in which two kinds of stimuli are presented 

 to an animal. One stimulus, called the 'unconditioned 

 stimulus 3 (US), is any stimulus that evokes some 

 definite response, called the 'unconditioned response' 

 1 I R), without any prior learning. In Pavlov's case, 

 the L'S was food and the UR was salivation. Another 

 stimulus, the 'conditioning stimulus' (or after Learning 

 has occurred, the 'conditioned stimulus' 01 CS 1, is one 

 that prior to learning evokes no significant response. 

 In many of Pavlov's experiments, this was a bell. By 

 pairing the CS and the US, the one presented just 

 before the other, and doing this for a number ol trials, 



1 iin concern on this point has been considembh allayed 

 li\ the publication In Rusinov & Rabinovich (211) of an 

 admirable brief summary "i much material relevant to this 

 ■ hapter. 



