ISO BRAIN MECHANISMS AND LEARNING 



Pavlovian test by direct application of an electric shock to the animal's paw. Yet 

 to us, the difference seems considerable, hi Pavlov's test, the subject draws away 

 the paws from the source of stimulation, thus displaying an adaptative behaviour, 

 which terminates in a reverse afferent drive, in our sense of the word, indicating 

 that the animal has avoided the impact of the electric current. Besides, Dr Doty in 

 his experiment shows the movement of limbs as the mechanical effect of a stimula- 

 tion wliich, after having been subject to association, is now conveyed outwards 

 onto the motor system. This proves admirabK' the capacity of the brain tissue to 

 register any sequence of induced stimuli. 



I wish, in concluding, to draw your attention to one miportant factor, which is 

 of particular relevance, to Dr Hernandez-Peon's remark on the possibility of 

 showing pure cortico-cortical connections. Our laboratory has shown that the 

 most insignificant stimuli, as well as lesions of the cortical tissue will instantly 

 involve subcortical formations, and possibly, reticular ones. Tliis is why, by the 

 very nature of the process, no subsequent effects of stimulation can be only cortical. 



Doty. In reply to Dr Anokhin — I think we must simply adopt the mechanistic, 

 objective approach which Pavlov used so successfully. If I form a conditioned reflex 

 by using an avoidable, painful, 'biologically significant' stimulus to a forepaw so 

 that the animal lifts it when a tonal conditional stimulus is sounded, and for the 

 other paw proceed as Giurgea and I have done so that the other paw is hfted when 

 the 'auditory anahser' is stimulated directly at the cortex, you would be unable to 

 tell me simply by looking at the animal's behaviour, which conditioned reflex was 

 which. True, by careful analysis I suspect you would find great differences in the 

 autonomic nervous system responses to the stimuli employed, at least during some 

 stages of the training. But their absence in the latter case only proves them to be an 

 unnecessary complication in the process of establishing the neural alteration 

 responsible for the change in effect of the conditional stimulus. Both tone and 

 direct electrical stimulation of the 'auditory analyser' are initially without effect on 

 somatic musculature save possibly for an 'orientation reflex' which is soon lost. 

 Both become effective on the same motor apparatus in approximately the same 

 number of trials. Both states are subject to the laws of conditioning, i.e. there is no 

 apparent backward conditioning, there can be external inhibition, they can be 

 extinguished. Why then call them different states or infer for them different 

 mechanisms f 



We have shown that if the ventral roots are crushed and an animal immobilized 

 with bulbocapnine, it can still be conditioned to make conditioned reflexes with its 

 hind leg even though the leg has never moved during conditioning. Thus we can 

 show proprioceptive feedback from the unconditioned reflex to be unnecessary for 

 the formation of conditioned reflexes. This does not say, that such factors are not 

 normally present; only that they need not be. Such experimental simplification ot 

 the situation certainly does not alter significantly the process we desire to elucidate, 

 nor change its name. In similar vein the elimination of motivational factors must 

 not be construed to infer qualitatively different processes to be operative in 

 'cortical-cortical' conditioning as compared to the more usual procedures which 

 involve such unknowns as 'biological purpose' or unanalysable emotional and 

 subjective factors. 



