36 K. S. LASHLEY 



a significantly greater number of trials for relearning of the 

 visual habit than are required in the original learning (except 

 perhaps in cases of thalamic lesion). The operative de- 

 struction, therefore, did not interfere with the capacity to 

 relearn any more than it did with the capacity for original 

 learning. Only the after-effects of previous training were 

 reduced or abolished. 



This result is in general accord with previous findings for 

 the motor habits of the 'inclined plane' and 'double-platform' 

 boxes (Lashley and Franz, '17; Lashley, '20) in the rat, 

 where it was shown that habits destroyed by injury to the 

 frontal regions are reacquired with normal facility; with 

 Franz's findings ('07) for motor habits in cats and monkeys 

 when the frontal lobes are destroyed, and for monkeys after 

 lesions in the visual areas (Franz, '11). Data on aphasia 

 (Franz, '24) indicate that in man also relearning of habits 

 lost through cerebral insult may progress at normal rate. It 

 is true that this rapid recovery in man is not invariable, but, 

 as Monakow states, the unimprovable cases are those of ex- 

 tensive diffuse lesions. They therefore probably correspond 

 to the cases of very extensive lesion in the rat (Lashley, 

 '20) in which learning is definitely retarded. 



If, as seems clearly established, these smaller lesions do 

 not lessen the animal 's ability to learn, we must conclude that 

 no part of the cerebral cortex is better adapted for the for- 

 mation of any particular habit than is any other. Any ana- 

 tomically continuous cerebral area may serve the learning 

 function, provided it presents a sufficient mass. This must 

 mean that in a problem situation the effects of stimulation 

 irradiate to all parts of the cortex. As the habit is estab- 

 lished there comes into being a definite structural modifica- 

 tion having topographical position and capable of destruction 

 by brain injury. The learning process is independent of 

 locus, whereas the mnemonic trace or engram has a definite 

 localization.^ 



' The problem of localization is perhaps even more complicated than these data 

 indicate. I have records of two animals in which practically all of the cortex 



