92 BRAIN MECHANISMS AND LEARNING 



feeding centre are by no means removed by the new training but the new connec- 

 tions are formed independently of them. 



This suggests a form of continuity between the inborn reflexes, imprinting and 

 normal conditioning and shows that there arc perhaps no sharp limits between 

 these phenomena. Experiments made long ago in Pavlov's laboratory by Citovitch 

 are also relevant here. This author found that the alimentary reflex to the smell of 

 tood is not inborn but conditioned because it appears only after a few reinforce- 

 ments of the stimulus, but this reflex is established very rapidly and is then very 

 stable. I think that we could label this phenomenon either as conditioning or as 

 imprinting. 



Thorpe. Some experiments have been done with deafened birds by Schwartakoft 

 and Messmer. The production of the essential elements in an innate song is not 

 fundamentally affected by being deafened but there may be a change in the overall 

 'pitch' of the song. This seems to provide a sharp distinction from conditioning. 



EsTABLE. In certain species of birds, males sing more and more and differently 

 when exliilarated by the presence of the female or when after being in the neigh- 

 bourhood of the female the latter is removed from his sight. Hormonal influences 

 have been mentioned as possible explanation of this, but though they are probably 

 necessary, they cannot be suflicient to explain the production ot such a variety oi 

 songs. Besides, an exclusively endocrine mfluence cannot explain the flict that the 

 male sings better than the female; the nervous system and tlie sound-producing 

 apparatus must necessarily participate. 



When the male bird is in the presence of the female, it sings ; if the latter is removed, 

 it sings even more. When the female is absent it stops singing. What happens in 

 the brain of the male bird would be interesting to know. Is there some endocrino- 

 logical influence in the mechanism of the brain which conditions this behaviour ; 

 For example, the problem of the gestalt theory if the conditioned reflex is the 

 cause, if it is first or second. I have talked on this subject with Kohler, who was a 

 pioneer in this field. He believes that the gestalt structures precede conditioning. 



Segundo. To complement the observation of Dr Baser I would like to note that 

 we have implanted electrodes in the mesencephalon of the Tero bird [Beleuopterus 

 chilciisis). Electrical stimulation with threshold voltage produced investigation or 

 orientation movements; with higher voltages, the bird stretched its wings, started 

 to fly and in addition, squawked loudly. (Silva, Estable and Segundo, unpublished 

 observations.) 



Grastyan. a marked following reaction could be observed in some oi our 

 experiments by stimulating the hypothalamus in cats. This behaviour seemed to be 

 also in close correlation with the function of the rhinencephalon. You say that 

 there is a limited period of the animal's life when this reaction can occur naturally. 

 In which stage of maturation of the central nervous system does this reaction occur? 

 Which structures are responsible for its integration in the birds? 



Doty. I have seen this following reaction consistently in cats deprived of all 

 visual cortex in infancy. They will approach and follow moving acoustic stimuli 

 and persist in this activity for minutes. 



Grastyan. l^r Adey has made similar observations, after the destruction ot the 

 cntorhinal cortex in the marsupial phalanaen. 



Adey. After a limited reaction of the hippocampus cortex which forms the 

 entorhinal area. The animal was tamed and at the same time would follow anv 



