STUDIES OP CEREBRAL FUNCTION IN LEARNING 277 



probable that the loss in this case is due to the fact that the frontal 

 region is an important somaesthetic projection area as well as electro- 

 stimulable. The one case for which there is clear evidence is the 

 group of somaesthetic habits of the discrimination box which determine 

 general orientation, finding of food, responses to doors, prompt correc- 

 tion of errors, &:c. These survive the destruction of any given third of 

 the cortex [10] and of the subcortical cerebral nuclei. It is possible 

 that they are formed at levels below the cerebrum ; it is certain that 

 they are not dependent upon the so-called motor structures. 



There is some evidence, to be reported later, that the habit of the 

 " double platform box " [10] is disturbed but not completely abolished 

 by destruction of either the frontal or the occipital regions. This 

 suggests that more complex habits involving diverse sense organs may 

 demand co-ordination of distant portions of the cerebrum and that the 

 visuo-motor habit dealt with in this study is too simple to give a typical 

 picture of cerebral function. It does not, however, indicate any greater 

 importance of the pyramidal tracts in complex habits, and we may 

 conclude that the existing evidence for the rat all opposes the direct 

 participation of the " motor areas " in the performance of any habit. 



The Function of the Stimulable Area and the Caudate 



Nucleus in the Rat. 



The evidence that the stimulable cortex in the rat has no direct 

 function in the performance of habitual motor adjustments seems 

 conclusive. What then is the function of this portion of the cortex ? 

 Data for a final answer to the question are not available, but some 

 suggestions are given by the motor disturbances following unilateral 

 lesion to the stimulable area and the caudate nucleus. 



Immediately following combined unilateral destruction of the 

 caudate nucleus and the stimulable cortex the animal shows a very 

 pronounced rotation toward the injured side. Left undisturbed, he 

 assumes a normal position, but immediately upon stimulation he bends 

 sharply toward the side of the injury and walks in a circle, sometimes 

 so narrow that the head is brought across the hind quarters or trips up 

 the hind feet. The legs of the side opposite the injury are hyper- 

 extended and spastic (fig. 15c). This condition may persist for several 

 weeks, but usually clears up within a few days to such an extent that, 

 when the animal is placed in a large open space and allowed to become 

 orientated, he is able to walk in a straight line. But the tendency to 



