266 OEIGINAL ARTICLES AND CLINICAL CASES 



The data from these animals, in conjunction with that presented in 

 earlier papers, establishes the fact that the rat may form somsesthetic 

 motor habits in the absence of the stimulable cortex and of the caudate 

 Duclei. I have shown that destruction of the stimulable area alone does 

 not lead to an appreciable reduction in the rate of formation of visual 

 habits, and that a difficult latch box, the "double platform box," may 

 be learned at normal rate after complete destruction of the stimulable 

 areas and severe injury to one or both caudate nuclei [10]. Of the 

 three animals reported in the present study, No. 19 alone survived 

 long enough to allow of acquirement of the visual habit and in this 

 animal the left caudate nucleus and part of the right were uninjured. 

 In the other two, however, the stimulable cortex was destroyed and the 

 caudate nuclei were either destroyed, as in No. 17, or severed from 

 their thalamic connections, as in No. 18. These animals survived 

 only a short time, but both gave unmistakable evidence of the formation 

 of simple somaesthetic-motor habits. From the data on the retention of 

 visual habits after the same operation, presented in the following section, 

 it is probable that the animals would have formed the visual habit if 

 training could have been continued. 



The problem of the relation of the extent of cerebral destruction to 

 the complexity of the habits which may be formed must be reserved for 

 later discussion when more adequate experimental data are available. 

 The interest of the present study is chiefly in the question of whether 

 or not habitual " voluntary " movements are mediated by the stimulable 

 areas. These experiments show clearly that neither the stimulable area 

 nor the caudate nuclei are necessary for the acquirement of such move- 

 ments. This is in agreement with the results of Kothmann [16] with 

 monkeys and justifies the conclusion that the so-called motor areas are 

 not essential to the acquirement of voluntary activities. 



This at once suggests the more important question of whether under 

 normal conditions the motor areas are directly functional in the 

 performance of habitual reactions. This problem has been attacked by 

 destroying the structures after a complex habit had been acquired and 

 testing for retention of the habit after the operation. 



Tin Retention of Visuo-motor Habits after Destruction of 



the Stimulable Areas and the Caudate Nuclei. 



For tests of retention after operation the animals were trained in the 



crimination box until they made thirty consecutive trials without an 



When this record was attained the problem was considered 



