PART ONE 



TRANS-SYNAPTIC DYNAMICS 



The performance of any overt act, by any but the most primitive 

 of organisms, is accomplished by the contraction and relaxation of 

 groups of specialized cells called muscles. Normally these contractions 

 and relaxations, by whatever mechanisms they may be effected, are at 

 least initiated by prior events occurring at the junctions with these 

 muscles of certain other specialized cells called neurons. Whatever 

 the nature of these prior events, and by whatever mechanism they 

 are effected, they are themselves initiated by a sequence of still prior 

 events in the neurons themselves, and these in turn by yet earlier 

 events at the junctions of other neurons with these. Thus regressing, 

 step by step, we conclude that apart from possible cycles, pools of 

 perpetual activity, the whole sequence was started by an initial set 

 of events at the points of origin of an initial set of neurons. And 

 finally this ultimate set of initial events — the set, or any member of 

 the set, according to convenience, being called a stimulus — was 

 brought about by or consisted in some physical or physiological occur- 

 rence in the environment or within the organism. 



Doubtless there are often and perhaps always countless other 

 accompanying events occurring within the organism and interacting 

 to a greater or lesser degree with those events here mentioned, but 

 no scientific theory can account for everything, and still less for 

 everything all at once. We wish, therefore, to define our schematic 

 reacting organism as one consisting solely of receptors (sense-or- 

 gans) , effectors (muscles) , and a connecting set of neurons, the whole 

 and the parts being affected by the physical or physiological environ- 

 ment only insofar as this acts as a stimulus via the receptors. We 

 wish to consider to what extent behavior can be accounted for in 

 terms of such a model. In undertaking such an inquiry, we freely and 

 expressly acknowledge that much is left out, and we emphatically 

 refuse to make any claim in advance as to the range of the behavior 

 that can be so accounted for. This is an empirical question to be ex- 

 perimentally decided. But a hypothesis cannot even be refuted until 

 it is clearly formulated. 



The structure of a neuron is fairly complicated and its behavior 

 is hardly less so. Consequently, to make progress the neurons, too, 

 must be schematized. Structurally there is a cell body and two or more 



