io8 



BRAIN MECHANISMS AND LEARNING 



same manner as was assumed by Lorente de No (1934, 1938) and his 

 followers for the activity of the central nervous system in general. In any 

 case, there are sufficient grounds for this assumption during the stage of 

 formation of conditioned reflexes and for the initial period of their func- 

 tioning. Subsequently, depending on a number of circumstances, evolu- 

 tionary development leads to different results: to the inhibition of both 

 conditioned connections, to the inhibition of one of them, and some- 

 times to the preservation of both connections in a state of stability and 

 efficiency. In this case a usual one-way conditioned coiuiection can be 

 regarded as a derivative of a double conditioned connection, as resulting 

 from the subsequent inhibition of one of the paired connections. 



Fig. 8 



Schematic representation of a conditioned reflex arc. 



I should like also to point out that all the factual material described in 

 this communication, as well as the appraisal of its scientific significance, 

 may also be regarded as corroborating the proposition we advanced many 

 years ago, that the primary conditioned reflex results from the synthesis 

 of combined inborn reflexes evoked by both unconditioned and 'in- 

 different' stimuli (Fig. 8). 



Of course, at present, we arc far from a satisfactory interpretation ot 

 these facts. Nevertheless, some purely hypothetical statements can be made. 

 In particular, we are inclined to believe that the elaboration of a double 

 conditioned connection may be accounted for by the relative equality of 

 intensity of the excitations which arise in the corresponding central 

 nervous structures under the influence of the combined stimuli. It goes 



