CEREBRAL FUNCTION IN THE RAT 133 



simple habits after the complete destruction of all the cortex of 

 the frontal, temporal, and parietal regions and the greater part 

 of that on the orbital surfaces. This includes all the regions to 

 which the function of habit formation has been ascribed and 

 leaves only those which have been thought to have visual, audi- 

 tory, and olfactory functions. The destruction of cortical tissue 

 has not been extensive enough to prove that learning may take 

 place wholly at the level of the sub-cortical centers but the evi- 

 dence at hand is sufficient to justify more extensive experiments 

 upon this point. The ability of the animals to form habits 

 after the loss of those parts of the brain which are normally used 

 in learning, the reestablishment of motor control after the loss 

 of the stimulable area of the cortex and of the corpus striatum, 

 and the seeming equipotentiality of the different parts of the 

 frontal pole in the functioning of complex habits go far toward 

 establishing the complete functional interchangability of all 

 parts of the cerebral cortex. 



SUMMARY 



Rats were trained after destruction of various parts of the 

 cerebral cortex including the frontal, temporal, parietal, and a 

 large part of the orbital surfaces and the influence of the cerebral 

 destruction upon their ability to form and retain kinesthetic- 

 motor habits was tested. It was found that: 



1. The habit of turning correctly in the simple maze may be 

 retained after the destruction of any part or all of the cortex 

 lying in front of and above the knee of the corpus callosum and 

 after the destruction of any part of the temporal and parietal 

 regions. 



2. The maze-habit may be acquired after the destruction of 

 all the cortex included within these areas, and after the destruc- 

 tion of one, perhaps both, of the striate nuclei. 



3. The more complex habits involved in opening the inclined- 

 plane box are retained after destruction of the temporal regions 

 of the cortex. 



4. The complete destruction of the frontal regions of the 

 cortex results in the loss of the inclined-plane box habit. 



