HOW DO RATS LEARN? 177 



and in higher mammals the disturbance of motor 

 function becomes progressively greater as the zoolog- 

 ical scale is ascended. Even in man, however, where 

 loss of the ''motor cortex" nearly or quite abolishes 

 voluntary control of the affected muscles, some such 

 control may be subsequently regained. The signifi- 

 cance of this so-called motor cortex is, accordingly, 

 one of the most puzzling problems in neurology. 



9. What is the relation of the cortex, and par- 

 ticularly of the frontal cortex, to the corpus striatum 

 in habit formation? This general theme has already 

 been discussed, and it seems clear that in the course 

 of vertebrate evolution there have been remarkable 

 changes in the relations between cortex and striatum. 



In Lashley's experiments on rats there was no 

 evidence that the corpus striatum has any significant 

 relation to the learning process except as unsym- 

 metrical lesions of the striatum produced motor dis- 

 turbances which affected the course of the reactions. 



10. Finally, there is evidence in higher mammals 

 that the frontal lobes have unique significance in the 

 learning process (Franz, 1907; Lashley and Franz, 

 1917; Bianchi, 1922). 



The later members of this series of questions (6-10) 

 will be examined further in the following chapters. 



