THE PROBLEM 1/7 



1/6. The nervous system is well provided with means for action. 

 Glucose, oxygen, and other metabolites are brought to it by the 

 blood so that free energy is available abundantly. The nerve 

 cells composing the system are not only themselves exquisitely 

 sensitive, but are provided, at the sense organs, with devices of 

 even higher sensitivity. Each nerve cell, by its ramifications, 

 enables a single impulse to become many impulses, each of which 

 is as active as the single impulse from which it originated. And 

 by their control of the muscles, the nerve cells can rouse to 

 activity engines of high mechanical power. The nervous system, 

 then, possesses almost unlimited potentialities for action. But 

 do these potentialities solve our problem ? It seems not. We 

 are concerned primarily with the question why, during learning, 

 behaviour changes for the better : and this question is not 

 answered by the fact that a given behaviour can change to one 

 of lesser or greater activity. The examples given in S. 1/5, 

 when examined for the energy changes before and after learning, 

 show that the question of the quantity of activity is usually 

 irrelevant. 



But the evidence against regarding mere activity as sufficient 

 for a solution is even stronger : often an increase in the amount of 

 activity is not so much irrelevant as positively harmful. 



If a dynamic system is allowed to proceed to vigorous action 

 without special precautions, the activity will usually lead to the 

 destruction of the system itself. A motor car with its tank full 

 of petrol may be set into motion, but if it is released with no driver 

 its activity, far from being beneficial, will probably cause the 

 motor car to destroy itself more quickly than if it had remained 

 inactive. The theme is discussed more thoroughly in S. 20/12 ; 

 here it may be noted that activity, if inco-ordinated, tends merely 

 to the system's destruction. How then is the brain to achieve 

 success if its potentialities for action are partly potentialities for 

 self-destruction ? 



The relation of part to part 



1/7. It was decided in S. 1/5 that after the learning process the 

 behaviour is usually better adapted than before. We ask, there- 

 fore, what property must be possessed by the neurons, or by the 

 parts of a mechanical ' brain ', so that the manifestation by 



5 B 



