XVI 



Actions and How They Are Performed 



H 



We have been discussing how the brain deals with the messages it 

 receives from the senses, and how it reduces them to a useful form 

 by finding significant patterns in them. We have now to go a step 

 further and see how these patterns or pictures are translated into 

 actions, which enable the animal to satisfy its needs and to continue 

 to live — actions which are often extremely complicated. 



There seem to be two chief ways by which these actions are 

 stimulated and controlled — and both ways have been developed in 

 animals to a quite extraordinary degree. 



INSTINCT 



First, there is the instinctive response. The animal is in a situation 

 which it has not met before, but nevertheless it is able to perform 

 very complex actions, the purpose of which cannot be known to it. 

 Under these circumstances the ability to perform these actions must 

 be innate, i.e. the animal is bom with it. 



Chickens can run about soon after being hatched and will peck at 

 any small, bright object; a calf or newly-born rabbit is soon able to 

 suck from its mother. Birds can fly, when their wing feathers have 

 developed, with little or no practice. These are all complicated 

 muscular actions. They involve bringing great numbers of muscles 

 into action, each in the right order and at the right time. The signals 

 which stimulate these muscles must reach their destination at just the 

 right times. These signals must be dispatched by the brain and it 

 follows that in such cases the pattern of nervous stimulation which 

 produces the action must be present in the animal's brain at birth 

 only requires a suitable stimulus to cause it to function. Thus no 



