W. H. THORPE 93 



moving object. This was not accompanied by any aggressive behaviour towards 

 the object they were following. They normally attack with jaws or teeth objects 

 that come within the visual field. This ceases after ablation of the entorhinal cortex. 



Magoun. I am glad to hear reference to the rhinencephalic or limbic brain in 

 this connection because I think attention should be called to the generalizations of 

 Paul Maclean that this part of the C.N.S. is concerned with these types of behaviour 

 which preserve the individual on feeding or aggression or defence, and which 

 preserve the race by managing sexual behaviour. 



Hernandez-Peon. The curves that Dr Thorpe showed us concerning the rate 

 ot development of internal inhibition may explain the great individual variation 

 observed during experimentally induced habituation. I wonder if he could elabo- 

 rate the matter further and tell us what is the presently available evidence obtained 

 by using a systematic approach. Wliat kind of responses have been tested and 

 which animals have been studied f 



Thorpe. The subjects were all birds ot tlie following species: Canary {Scriiiiis c. 

 caiiariiis). Greenfinch {Cliloris chloris) and Great Tit [Pants itiajor). These curves refer 

 to string-pulling behaviour and to learning to take food from two types of dishes, 

 one with a black lid and one with a white one. In the string pulling the wild bird, 

 it it learns the trick at all, often behaves with extreme precision and the whole 

 movement appears highly organized. In experimental studies, however, the birds 

 present very varied behaviour. This, we hope, will be explained in the future as a 

 result of this discovery of the diiferent rates of change of these factors, namely the 

 level of responsiveness and of internal inhibition, which arc themselves partly an 

 expression of the previous experience of the bird. 



