90 K. S. LASHLEY AND S. I. FRANZ 



was destroyed in one or another of these animals without inter- 

 fering in any way with the formation of the relatively complex 

 habit. In numbers 3, 6 and 7 the lesions were small but in 

 numbers 1 and 4 there was a loss of practically the entire frontal 

 pole of both hemispheres without a correlated reduction of the 

 learning ability. 



It seems quite certain, therefore, that no particular part of 

 the anterior third of the cortex of the white rat is necessary for 

 the formation of a complex kinesthetic-motor .habit and, from 

 the condition in numbers 1 and 4, that the entire frontal region 

 of the cortex may be dispensed with without any reduction of 

 the ability to learn. 



IV. RETENTION OF THE INCLINED-PLANE HABIT AFTER 

 CEREBRAL LESIONS 



Earlier experiments with the higher mammals indicate that 

 learning may take place in the absence of parts of the cortex 

 which are normally functional in habit formation. Thus, 

 Franz (3) has found that the destruction of the frontal lobes in 

 the cat and monkey is followed by the loss of recently formed 

 habits but that the habits can be immediately reacquired and 

 that the rate of learning is practically the same as before the 

 loss of these areas. The ability of the animals described in 

 series III to learn the inclined plane problem does not, there- 

 fore, preclude the possibility that the frontal region of the cor- 

 tex is normally functional when present. To test this a series 

 of normal animals' were trained on the inclined plane box, then 

 operated upon to destory the frontal areas, and tested for re- 

 tention of the habit. Seventeen animals survived the opera- 

 tion and were tested thoroughly for retention or relearning of 

 the habit. 



In three animals the lesions were restricted to the dorsal and 

 temporal regions, first to test the relation of these parts to the 

 functioning of the habit, second, as a control of the effects of 

 operative shock. 



No final criterion of learning was adopted, but the animals 



