HOW DO RATS LEARN? 171 



directly compared. Animals with total destruction of 

 one cerebral hemisphere and those deprived of both 

 occipital lobes were slightly less active than normal; 

 and those with frontal injuries were more active than 

 normal. 



These differences in general activity must be taken 

 into account in evaluating the learning processes of 

 the operated rats, especially in the case of habits 

 primarily involving kinesthetic activity. In fact, 

 throughout the experiments it is clear that the par- 

 tially decerebrated animals had a distinct advantage 

 over the normals in learning these particular habits. 

 In some cases this is clearly due to the fact that the 

 less vigorous and frisky animals adjusted to the 

 conditions of the experiment more readily than the 

 more active ones; in other cases it is unexplained. The 

 author found no evidence for any general disturbance 

 of the reflex and instinctive reactions which might 

 account for marked difference in learning ability 

 (1920, p. 73). But it must be kept in mind that ex- 

 tensive injuries of the cortex, those involving more 

 than 50 per cent of the cortical substance, and es- 

 pecially total destruction of the frontal cortex, do 

 affect general motility and do impair (and in some 

 cases abolish) the retention of kinesthetic-motor 

 habits. 



5. Is there any relation between actual amount of 

 cortex functioning and the rate of learning, irrespec- 

 tive of possible localization of specific functions.'' 



