TEMPERATURE REGULATION "CENTERS" 
repaired itself, if you will. The brain apparently has the ability to 
change its functional organization and so bring about a return of 
essentially normal output despite the loss of some parts. I have no 
notion of what this reparative or regenerative process might be. All 
I can point out is that the doctrine of centers does not take into 
account this plasticity of the brain in its formulations of the hypo- 
thetical function of various centers. 
THE ANALYSIS OF BEHAVIOR INTO ITS ELEMENTS 
These difficulties I have described so far are largely concerned 
with manipulative problems of stimulation, ablation, and recording. 
There are, in addition, some major observational difficulties con- 
cerned with how behavior is to be subdivided, and what behavioral 
elements are to be ascribed to specific sites. The assumptions are, 
in the doctrine of centers, that each center produces an organized, 
recognizable entity as its output, that the part of the brain respon- 
sible for each response is at a high energy level, and the others are 
quiescent. It is a doctrine of mutual exclusion. Consider as an 
example of these complex assumptions the phenomenon of reflex 
shivering, which we have already considered at some length. Specif- 
ically, is there any one part of the brain which is solely concerned 
with shivering and with no other reflex phenomenon? What parts of 
the brain are silent when shivering is going on, but when the animal 
is otherwise inactive? On the other hand, what parts of the nervous 
system concerned with shivering are also concerned with other 
types of behavior, whether thermoregulatory or not? 
Beginning with the periphery, it is obvious that cold receptors 
are not specific for shivering or, for that matter, even for thermo- 
regulatory responses. They can elicit a wide variety of autonomic 
or somatic responses depending upon previous circumstances, as 
with our experiment in stimulation of the prepyriform cortex. Nor 
can there be said to be shivering effectors, since the muscles are 
used also in a variety of other activities. 
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