CEREBRAL FUNCTION IN THE RAT 75 



knowledge. The adoption of methods looking toward the deter- 

 mination of other habit forms will result in more complete 

 information. 



Although it is commonly believed that habit formation is due 

 to the functioning of cerebral parts, and especially those parts 

 which are called cortical, it is by no means right to conclude that 

 all habit reactions are due to cerebral, or more restrictedly cor- 

 tical, activities. Leaving aside those reactions which must pass 

 by way of subsidiary stations, like the thalamus, as part of the 

 total reaction, it is doubtless the case that certain habits are 

 carried out by the exclusive use of non-cortical, and exclusively 

 also perhaps by non-cerebral parts. This is shown in the reactions 

 of the so-called lower animals, and it has been contended that 

 for the execution of some long-established habits in higher 

 animals only non-cerebral parts are needed. There is reason to 

 believe that in the brainless frog certain simple habits may be 

 acquired. One of the urgent needs at the present time both in 

 neurology and in the study of learning is the establishment of 

 the parts played by the different portions of the nervous system. 

 With these facts in hand it will not only be possible to under- 

 stand something of learning and forgetting, but at the same 

 time we shall be better able to appreciate that inadequately 

 named condition which is called cerebral vicarious functioning. 



Two main problems were in mind when the following work 

 was begun. One was the effects of different lesions upon habit 

 formation and retention, the second was the determination of 

 the parts needed for habit formation. These problems are 

 identical in some particulars, but they can also be considered to 

 be independent. It may be that in a normal animal a habit is 

 formed by the interaction of certain nervous elements, but that 

 when any of these elements have been destroyed or even inter- 

 fered with other elements may take their places. Or, it may 

 be that in the process of learning many different elements are 

 used at first, but that the number decreases as the habit is 

 acquired. 



The scope of the experiments described here has been limited 

 to a determination of the relation of the frontal pole and dorsal 



