122 K. S. LASHLEY 



/"' These cases suggest that there is an actual difference in the 



( effects of unilateral and bilateral destruction; that destruction of 

 the corpus striatum does not actually eliminate the coordinating 



/ mechanism, but merely destroys the balance of some regulatory 

 mechanism which is useful when functioning normally but which 



x may be dispensed with altogether provided that the loss is bilat- 

 eral. Such a situation would be analogous to that presented by 

 the semicircular canals, but more experimental data must be 

 accumulated before the point can be established. 



The function of the motor area in learning 



These observations on paresis indicate that the stimulable cor- 

 tex and some part or all of the corpus striatum have a similar 

 motor function. Is it possible that neurones in either one of 



f these structures may function as the final common path of a 

 learned reaction in the absence of the other? If this were true 

 it would explain the seeming restriction of visual habits to the 

 occipital pole (section V) and the failure of complete destruction 

 of the excitable cortex to abolish simple kinaesthetic-motor hab- 

 its. The records include two cases which speak strongly against 

 this, however. They are animals number 10* and 11* (plate 

 IV, figures 10 and 11). Both of these animals showed complete 

 destruction of the excitable cortex as a result of the two succes- 

 sive operations to which they were subjected and also very ex- 

 tensive injuries to the corpora striata. Nevertheless, both 

 showed practically perfect retention of the simple maze. It is 

 possible that the portions of the corpora striata remaining were 

 sufficient to mediate the habit, but it seems unlikely that such 

 extensive injuries to a functional area should not have produced 

 some deterioration. Further, a number of cases (table 9) appear 

 in which extensive injury to both corpora striata and the excit- 

 able cortex was not followed by any marked loss in ability to 

 learn. Such results suggest that the motor areas may not be 

 important for learning as such; that the function of the motor 

 cortex may be maintenance of normal muscle tone and that 

 habitual reactions may be superimposed upon this by impulses 



