64 BRAINS OF RATS AND MEN 



The experiments cited by Lashley in refutation of theories of 

 diffusion and "drainage" or "induction" are far from convincing. 

 These concepts have doubtless been greatly overworked by theor- 

 ists, but in their elementary forms they rest upon a large body of 

 experimental data. It is true that our knowledge of the precise 

 mechanisms employed in irradiation, in "drainage," in facilita- 

 tion by use, and in the fabrication of new learned patterns of 

 behavior is still incomplete, but the cases cited by Lashley in 

 refutation of these theories and of the doctrine of variable synap- 

 tic resistance are in reality wholly irrelevant, as a neurological 

 analysis of the experimental data would show. 



It would be out of place here to go into the technical details of 

 such a neurological analysis. In one passage Lashley substitutes 

 for the current theories mentioned above the utilization of effer- 

 ent paths which were not functional during learning. After de- 

 struction of the arm area of the right precentral gyrus of a 

 monkey and subsequent training of the right hand with a prob- 

 lem-box, the arm area of the left cerebral hemisphere was then 

 destroyed. It was later found that there was almost perfect 

 transfer of the habit from the trained but now enfeebled right 

 hand to the untrained left hand which had been partially para- 

 lyzed throughout the training but was now almost fully re- 

 covered. From this it is concluded, "We have evidence of the 

 utilization of neural paths in the performance of a learned reac- 

 tion which were not activated during the course of learning. In 

 this case the drainage theory is definitely ruled out." 



This is a gratuitous assumption, for there is an immense com- 

 plexity of neural architecture in addition to that of the precentral 

 gyrus which was certainly involved in this training and which 

 may have been entirely unaffected by the operations, and drain- 

 age or any other process which one wishes to hypothecate may 

 have been involved in the transfer of the training to the other 

 hand. These monkeys had damage done only to a sector of the 

 final common path which may be utilized not only by this habit, 



