1/2 DESIGN FOR A BRAIN 



Behaviour, reflex and learned 



1/2. The activities of the nervous system may be divided more 

 or less distinctly into two types. The dichotomy is perhaps an 

 over-simplification, but it will be sufficient for our purpose. 



The first type is reflex behaviour. It is inborn, it is genetically 

 determined in detail, it is a product, in the vertebrates, chiefly 

 of centres in the spinal cord and in the base of the brain, and it is 

 not appreciably modified by individual experience. The second 

 type is learned behaviour. It is not inborn, it is not genetically 

 determined in detail (more fully discussed in S. 1/9), it is a product 

 chiefly of the cerebral cortex, and it is modified markedly by the 

 organism's individual experiences. 



1/3. With the first or reflex type of behaviour we shall not be 

 concerned. We assume that each reflex is produced by some 

 neural mechanism whose physico-chemical nature results inevit- 

 ably in the characteristic form of behaviour, that this mechanism 

 is developed under the control of the gene-pattern and is inborn, 

 and that the pattern of behaviour produced by the mechanism is 

 usually adapted to the animal's environment because natural 

 selection has long since eliminated all non-adapted variations. 

 For example, the complex activity of ' coughing ' is assumed to 

 be due to a special mechanism in the nervous system, inborn and 

 developed by the action of the gene-pattern, and adapted and 

 perfected by the fact that an animal who is less able to clear its 

 trachea of obstruction has a smaller chance of survival. 



Although the mechanisms underlying these reflex activities are 

 often difficult to study physiologically and although few are known 

 in all their details, yet it is widely held among physiologists that 

 no difficulty of principle is involved. Such behaviour and such 

 mechanisms will not therefore be considered further. 



1/4. It is with the second type of behaviour that we are con- 

 cerned : the behaviour that is not inborn but learned. Examples 

 of such reactions exist in abundance, and any small selection 

 must seem paltry. Yet I must say what I mean, if only to give 

 the critic a definite target for attack. Several examples will 

 therefore be given. 



A dog selected at random for an experiment with a conditioned 



2 



