i8o BRAINS OF RATS AND MEN 



tions upon the visual cortex before and after training 

 were carefully studied statistically with adequate ex- 

 perimental and anatomical controls. 



In the case of some kinesthetic-motor habits it has 

 been shown that the habit is preserved (perhaps in an 

 impaired form) if even a small part of the frontal cor- 

 tex is left intact, though it is totally lost if the entire 

 frontal cortex is destroyed (see p. i86). The relation 

 of the visual habit to the occipital cortex is similar. 

 Lashley says: 



There is indication that, e.g., any extensive but incomplete 

 destruction of the visual areas of both hemispheres in the rat is 

 followed by inaccuracy of brightness discrimination, with great 

 variability from day to day, such as has been reported by Franz 

 in 1916 for aphasia, yet without any complete loss of any phase 

 of the visual function. 



In the final report on these experiments (1926) the 

 results are summarized as follows: 



Injuries to the occipital region inflicted before training and 

 including every possible part of the occipital third of the cerebrum 

 have no effect upon the ability of the animals to form the habit 

 of brightness discrimination. Total destruction of the "visual" 

 area does not reduce the speed with which a simple visual habit 

 may be formed. 



Injuries in the same region produced after the habit was 

 established resulted in a weakening or total loss of the habit. The 

 loss, as measured by the amount of practice necessary to re- 

 establish the habit, was closely proportional to the extent of the 

 injury and independent of its locus within the occipital third of 

 the cortex. 



Evidence is given to show that the loss of the habit is not the 



