W. H. THORPE 91 



song birds which arc, ot course, very active and mostly small. We have started 

 some ablation experiments with song birds, but these have not got very far yet. It 

 is as yet very difficult to stimulate the brain of a very small bird so that it will behave 

 in a fairly normal fashion and still sing. I think it will be some rime before the 

 technique is developed to the point at which signihcant results will begin to accrue. 



Fessard. What about parrots f 



Thorpe. Parrots should certainly be easier to investigate but, although they have 

 of course an astonishing facility for vocal mimicry, would not be much good tor 

 the study of the innate sounds. In this matter of vocal imitation the Indian hill 

 mynah excels even the parrots. But perhaps the most puzzling feature is that 

 neither parrots nor mynahs appear to use their power of mimicry in the wild at all 

 (Thorpe, 1959). They have stereotyped cries and calls which seem to serve tor 

 co-ordinating the movements oi the tiock but show no sign of mimicry. From the 

 point of view of the study of vocal learning these species would be admirable; but 

 not for studying mechanisms tor innate sound production. 



BusER. It might be of interest to mention here observations made in Paris by 

 Dr Rougeul and Dr Assenmacher, studying the electrical activity of deep brain 

 structures in unanacsthetized ducks by stereotaxic methods: each time when simply 

 introducing or moving up and down the Horsley-Clarke electrode, the animal 

 would start quacking whenever a certain level was reached. King in the tegmental 

 midbrain. Electrical stimuli were not systematically tried and the mechanical 

 excitation produced h\ the electrode appeared actualK' surticient to produce the 

 described effect. 



KoNORSKl. I would like to make two comments. The tirst one is this: As far as I 

 know, only birds, and among mammals only man, have the ability ot reproducing 

 sounds, i.e. they possess what mav be called acoustic-vocal reflexes of a specitic 

 kind. This ability seems to indicate that in these animals direct connections exist 

 between the acoustic area and the part of motor area concerned with vocalization. 

 We know that in man such connections in fict exist between anterior temporal 

 area and frontal opercular region. If the}- are destroyed the peculiar torm of 

 asphasia ensues. The patient understands what is said to him and is even able to 

 verbalize his thoughts, but he is not able to repeat exactly the words he hears. It is 

 much easier for him to say something spontaneously than to repeat it. It would be 

 very interesting to know whether such an acoustic vocal system exists in birds, and 

 if so, to study it both from anatomical and physiological points ot view. 



The second point concerns the problems of imprinting. We know trom exten- 

 sive experimental data (the literature is given in a paper by Konorski and SzweJ- 

 kowska, 1952) that classical conditioning shares one important property with 

 imprinting, namely its partial irreversibility. By the way, this is why I do not like 

 the term 'temporary connections' because these connections, once established, are 

 not temporary but stable, and, as I shall discuss later, they are not obliterated by 

 'disuse'. If you elaborate an alimentary conditioned reflex to some stimulus, it is 

 much more difficult to transform it afterwards into, say, a detensive conditioned 

 stimulus b}' changing the reinforcement trom tood to shock, than to elaborate the 

 defensive conditioned reflex to quite a new stimulus. Even after a long defensive 

 training of the alimentary conditioned stimulus, its previous alimentary role may 

 be detected. We explain these facts by saying that the old conditioned connections 

 established between the central representation of the conditioned stimulus and 



