E. A. ASRATYAN lOI 



The matter is entirely different with a reverse conditioned reflex connec- 

 tion between unconditioned stiniuh. They greatly resemble, especially 

 in their fragility and irregularity, conditioned connections between in- 

 different stimuli. It must be pointed out that a reverse connection, is so 

 feeble, so unstable, multiphasic and diverse in its manifestations and 

 depends on so many factors for its functioning that initially we even 

 doubted its conditioned reflex nature. 



Some of the peculiar features revealed by the experiments of Lyan- 

 Chi-an in the functioning of reverse conditioned reflex connections are 

 of special interest. For instance, (S) evokes more easily the reflex corres- 

 ponding to (P) if the strength of (P) has been increased or if the excitability 

 of the central nervous structures is raised. By strengthening (P) or by 

 an increase in the excitability of the relevant nervous apparatus it becomes 

 possible to revive and activate the reverse conditioned connections even 

 when under usual experimental conditions they cease to manifest them- 

 selves. A similar result is obtained if (S) is weakened, or the excitability 

 of the corresponding nervous structures is lowered. For example, in an 

 experiment in which stimuli are applied in the sequences 'electrical shock 

 — food', the presentation of food evokes a conditioned reflex lifting of 

 the animal's leg more frequently and more distinctly if the leg was 

 previously stimulated by a stronger shock than usual, or if, prior to 

 the experiment, the dog was deliberately fed to satiety. The feature 

 common to these two different preliminary experimental manipulations 

 is that they both lead to the same picture of relative excitability or 

 excitation of the central nervous structures corresponding to these two 

 stimuli. 



In contrast to this, a prehminary strengthening of (S) or increase in 

 excitability of the nervous structures corresponding to its reflex leads to 

 inactivation of the nervous connection even when under usual experi- 

 mental conditions they function regularly and satisfactorily. Similar 

 results are obtained by a preliminary weakening of (P) or by a preliminary 

 decrease of the excitability of the relevant nervous structures. Let us, for 

 example, take again the type of experiments thoroughly studied by Lyan 

 Chi-an in which stimuli were applied in the sequence: 'electric shock — 

 food'. Here the presentation of food evokes no conditioned lifting of the 

 leg if the animal is in a state of fasting before the experiment, or if it is 

 given appetizing food at the beginning of the experiment, or if its leg is 

 first stimulated by a weak electric shock. It may be noted that although 

 these preliminary experimental manipulations are different, they have 

 something in common: in different ways they lead to the creation of the 



