102 K. S. LASHLEY 



technique. In previous work Dr. Franz and the writer obtained 

 formation of simple habits after somewhat more extensive in- 

 juries but unfortunately these animals were not tested in a more 

 difficult habit. 



What is the bearing of these results upon the problem of the 

 cerebral mechanism of learning? In the first place, they show 

 conclusively that there are in the rat no special association areas 

 to which is restricted the function of associating sensory and 

 motor projection areas. We know from earlier work that habits 

 of the type required by the double-platform box are normally 

 mediated by the frontal pole. But in the absence of this some 

 other part assumes its function. The same condition must be 

 true for any other so-called association area that may exist in the 

 rat's cortex. There may be association areas which can function 

 alternatively, but the operations have covered almost all combi- 

 nations of cerebral regions except bilateral frontal with occipital 

 and this possibility seems almost ruled out. 



Second, the work of Franz on cats and monkeys and of Franz 

 and the writer on the rat indicates that the cerebral reflex paths 

 functioning in certain habits are distributed uniformly to all parts 

 of the frontal region, since the destruction of one frontal lobe in 

 the higher forms or of any given part of the frontal pole in the 

 rat is not followed by loss of the habit and the destruction of the 

 entire frontal region does result in loss of the habit. The pres- 

 ent experiments indicate, further, that the organization of the 

 entire cerebrum of the rat must be along similar lines; that the 

 | /reflex connections involved in habits may be laid down in any 

 part of the cortex. Under normal conditions the frontal pole 

 perhaps offers less resistance to the reintegrating of the activities 

 required by the habit than do other parts, but the same integra- 

 tions may be formed readily elsewhere. 



The determination of the regions which actually did function 

 in the habit would have been of considerable interest. Franz 

 found that when the animal lacking the frontal lobe learned a 

 problem box, destruction of tissue adjacent to the first injury 

 resulted in loss of the habit. On the other hand, Ley ton and 

 Sherrington ('17) failed to locate the region which assumed motor 



