MECHANISMS OF LEARNING 191 



any third of the cortex, but if learned with cortex in- 

 tact it cannot be retained after total destruction of the 

 occipital cortex. It was also shown that the inclined 

 plane box habit acquired by a normal animal is im- 

 paired if part of the frontal cortex is destroyed and is 

 lost entirely after total destruction of the frontal cor- 

 tex. 



In Lashley's first paper (1920) no experiments 

 were reported which determined whether the more com- 

 plex double-platform box habit acquired by a normal 

 rat is retained after destruction of the frontal cortex. 

 Later (1921^, p. 277) he writes, "There is some evi- 

 dence, to be reported later, that the habit of the 

 *double platform box' is disturbed but not complete- 

 ly abohshed by destruction of either the frontal or the 

 occipital regions." It is probable, therefore, that this 

 habit, like the inclined plane box habit, involves some 

 participation of the frontal cortex in normal learning 

 and retention and, unlike the simpler problem-box 

 and maze habits, a co-operation of frontal and occipi- 

 tal cortex is also a factor in this normal learning pro- 

 cess. 



SUMMARY 



From the foregoing survey of the anatomical and 

 physiological evidence it is clear that the cerebral cor- 

 tex of the rat is structurally diverse in its different 

 parts and that this diversity of internal organization 

 is correlated, at least in part, with differences in the 

 subcortical connections of the different fields. These 



