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NEURONAL INTEGRATIVE MECHANISMS* 



Theodore Holmes Bullock 

 University of California at Los Angeles 



Integration is to put parts together into a whole. Such a process occurs 

 in organisms at many levels, from the subcellular to that of the community. 

 The levels of interest for the present purpose begin with a whole neuron, 

 therefore do not embrace an analysis of the mechanisms in the cell or its 

 membrane, and extend only one or two steps up the hierarchy, through 

 closely knit groups of neurons to relations between such groups, but not so 

 far as the level of the whole nervous system of any animal. This limitation 

 is not one of appropriateness but is imposed by our methods and present 

 understanding, as physiologists. 



Indeed our understanding of the actual mechanism of nervous integra- 

 tion, our insight into the unit behavior which might account for this subtle 

 and complex result, is so meager that it may be asked, what can we say ? 

 This paper makes no pretense of accounting for very much normal be- 

 havior, and will conclude by emphatically invoking as yet unknown levels of 

 interaction ; but it makes an effort to say what can be said today about the 

 properties of neurons which must be involved in, and in certain cases appear 

 even to account for, the observed integration. It goes little beyond a list of 

 the properties — each of which provides a degree of freedom or an available 

 mechanism for altering the input-output function. These properties gen- 

 erally are additive, so that with only a few it is possible to obtain rather 

 complex permutations. Still our knowledge permits a very limited foray 

 into the vast field of higher nervous integration, and I am emboldened for 

 it only because so few have undertaken to bring together the several mecha- 

 nisms that are now known (see Fessard, 1954, 1956), while one often still 

 hears instances of thinking on these problems in which the neurons are 

 treated as purely digital or are otherwise oversimplified. 



One further disclaimer is necessary. We must deal with observed prop- 

 erties of neural units even though they cannot be explained by current 

 theories of cellular mechanism. So we are not accounting for the properties ; 

 rather in enunciating the phenomena which may explain higher levels, we 

 are formulating the problems awaiting attack at molecular levels. 



Let us return to the definition of our problem. Integration, I said, para- 

 phrasing the dictionary, is to put parts together into a whole. 



* Aided by grants from the National Institutes of Health, the National Science 

 Foundation, and the University of California. 



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