194 BRAIN MECHANISMS AND LEARNING 



active factor the luomcnt the dog is placed in the stand and the reaction 

 emerges only at the moment the bell comes into play it will become clear 

 that the time of day, being a special stimulus, determines the quahty of 

 the reaction because of the creation of a specific subthreshold dommant 

 state ot the central nervous system (according to Uchtomsky) which 

 spreads to the working apparatuses owing to the trigger action of the 

 conditioned stimulus. 



The synthetic nature oi the relations between the conditioned reflex 

 and the external conditions ot the experiment, both as a whole and of its 

 individual components, may also be revealed under the usual conditions. 

 Suffice it to transfer the animal, that until then had responded with good 

 conditioned alimentary reflexes, to other surroundings (for example, a 

 lecture-hall for demonstration to students) and the conditioned stimulus 

 loses its conditioned reflex effect. In this case the synthesis elaborated from 

 the tonic afferent action of the usual experimental situation and the trigger 

 action ot the conditioned stimulus is disturbed and the conditioned reflex 

 disappears. 



The following question arose in our laboratory: does this process of the 

 synthesis of the situational and trigger afferent influences have any 

 preferable localization in the cerebral cortex? 



The experiments of our associate Shumilina, conducted over many 

 years and consisting in extirpation of the frontal lobes in dogs who had 

 conditioned reflexes elaborated in the two-sided stand, have shown that 

 the frontal lobes have a very definite relation to this function of synthesis 

 of the afferent stimulations of different quality. During the experiment all 

 the normal intact animals in the two-sided stand behave rather mono- 

 tonously, with certain insignificant variations. Since the different condi- 

 tioned stimuli are reinforced by a single portion of food on the different 

 sides of the stand, the animals elaborate an expedient habit of sitting 

 quietly during the intervals between the conditioned stimuli /// the niiddh' 

 of the stand. 



After removal of the frontal parts (six to eight according to Brodman) 

 all the intact animals begin to behave in a characteristic way immediately 

 following the operation — they keep running from one feeding trough to 

 the other as long as the experiment lasts. We have named these movements 

 'pendular' (Fig. 3). 



It might be assumed that these movements were one of the forms of 

 'motor restlessness' described by many authors after they had removed the 

 frontal areas of the animals' brains. However, a direct analysis of the 

 mechanism of these pendulous movements has shown them to be directly 



