INTRODUCTION 



This monograph is directed toward the explanation of behavior by- 

 means of testable hypotheses concerning the neural structures which 

 mediate this behavior. We use the word behavior, for lack of a better 

 term, in a very broad sense to cover any form of response to the en- 

 vironment, internal or external, whether it is acting or only perceiv- 

 ing, and whether the response occurs immediately or after long delay, 

 providing only the response is governed by nervous activity initiated 

 by occurrences in the environment. We are seeking to develop a 

 theory of the nervous system as the determiner of behavior. 



Data of anatomy and physiology are altogether inadequate — un- 

 less in the case of a simple spinal reflex — for tracing in detail the 

 progress of a nervous impulse from its inception at a receptor, 

 through its ramified course in the nervous system, to its termination 

 at the effector. We know pretty well where the fibers lead from the 

 retina; we known even in some detail where the different retinal 

 areas are mapped on the cortex ; we know a good deal about the inter- 

 action of one region of the cortex upon another, and we know many 

 details about the functioning of neural units. But how the neural 

 units are combined in the visual area to enable the organism to locate 

 an object seen and to act accordingly, how the nervous discharges 

 from the two retinas are shunted this way and that to combine and 

 emerge at the appropriate effectors, is not explained by existing ex- 

 perimental and observational technique. For solving such problems 

 it is necessary to create testable hypotheses, to be revised, replaced, 

 or expanded according to the outcome of the tests. 



The task of developing this theory is three-fold. First, an ideal- 

 ized model of the elementary units must be constructed in terms of 

 postulates governing their individual behavior and their interactions. 

 The model must be simple enough to permit conceptual manipula- 

 tion. The units we have designated neurons. Our neurons are defined 

 by the hypotheses we impose upon them, and it may turn out that not 

 the single neuron of the physiologist and anatomist, but some re- 

 curring complex of these is most properly to be regarded as its pro- 

 totype. The junction of neurons we refer to as a synapse, and where 

 the impulses from two or more neurons are able to summate in pro- 

 ducing a response in one efferent neuron, or in each of several, we 

 have also, briefly, referred to the set of these junctions as constitut- 

 ing a single synapse. Such usage, in harmony with that of Rashevsky 



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