DESIGN FOR A BRAIN 1/6 



less to a more beneficial, i.e. survival-promoting, form would 

 need a discussion far exceeding the space available. But in this 

 introduction no exhaustive survey is needed. I require only 

 sufficient illustration to make the meaning clear. For this pur- 

 pose the previous examples will be examined seriatim. 



When a conditioned reflex is established by the giving of food 

 or acid, the amount of salivation changes from less to more. And 

 the change benefits the animal either by providing normal lubri- 

 cation for chewing or by providing water to dilute and flush away 

 the irritant. When a rat in a maze has changed its behaviour so 

 that it goes directly to the food at the other end, the new behaviour 

 is better than the old because it leads more quickly to the animal's 

 hunger being satisfied. The circus animals' behaviour changes 

 from some random form to one determined by the trainer, who 

 applied punishments and rewards. The animals' later behaviour 

 is such as has decreased the punishments or increased the rewards. 

 In Man, the proposition that behaviour usually changes for the 

 better with learning would need extensive discussion. But in the 

 example of the finger movements and the compound microscope, 

 the later movements, which bring the desired object directly to 

 the centre of the field, are clearly better than the earlier move- 

 ments, which were ineffective for the microscopist's purpose. 



Our problem may now be stated in preliminary form: what 

 cerebral changes occur during the learning process, and why does 

 the behaviour usually change for the better ? What type of 

 mechanistic process could show the same self-advancement ? 



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. The 

 ramifications are followed by repeated stages of further ramifica- 

 tion, so that however small a change at any point we can put 

 hardly any bound to the size of the change or response that may 

 follow as the effect spreads. And by their control of the muscles, 

 the nerve cells can rouse to activity engines of high mechanical 



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