STUDIES OF CEREBRAL FUNCTION IN LEARNING 257 



the stimulable area and the corpus striatum. 1 In order that data 

 obtained from the rat may be applicable to higher forms it is neces- 

 sary, therefore, that both the stimulable cortex and the corpus striatum 

 be considered. My earlier study eliminated only the stimulable cortex 

 from the habit mechanisms. In the experiments reported below I have 

 tested the effects of simultaneous destruction of the stimulable areas 

 and the caudate portions of the corpora striata upon the rat's ability to 

 form and retain visuo-motor habits. The data outlined above make it 

 fairly certain that in the combined lesion we are dealing with structures 

 analogous in function to the stimulable areas of the primates and 

 that conclusions valid for higher forms may be drawn from the 

 experiments. 



The chief question which the following experiments were designed 

 to answer is, then, whether or not the structures of the rat's cerebrum, 

 injury to which produces motor disorganization, are directly concerned 

 in the performance of habitual acts. Visuo-motor habits are best 

 suited for such tests, since they are easily acquired and recognized. A 

 visual area in the occipital region is clearly defined and it has been 

 shown that cortical representation of the habit is retained after 1,400 

 trials of overtraining [11], so that the possibility that the habits are 

 carried out at subcortical levels is ruled out. 



The Topography of the Stimulable and Visual Areas of the 

 Cerebrum and of the Corpus Striatum in the Eat. 



The stimulable area in the rat includes the antero-dorsal third of 

 the cerebral cortex. It extends from above the anterior margin of the 

 hippocampus forward to the frontal pole, covering the median half of 

 the dorsal convexity in this region. On the frontal pole it extends 

 laterally and then caudally over the inferior orbital surface. Fig. 1 

 shows a composite map of the area in about twenty-five animals, with the 

 movements elicited by bipolar stimulation. In the majority of animals 

 the area does not extend so far caudally as in the diagram and only 

 movements a, d, i, j, and p can be elicited. 



The visual function seems limited to a small area on the dorsal 



1 Since the pyramidal fibres are scattered throughout the caudate nucleus it is impossible 

 to destroy the latter alone. In earlier work [10] I found one case with extensive degenera- 

 tion of the right caudate nucleus involving few of the pyramidal fibres and leaving the 

 greater part of the stimulable area intact. This animal showed an unusually rapid and 

 complete recovery from the motor disturbances following operation and led to the tentative 

 conclusion that the striate nucleus and stimulable cortex have interchangeable function. 



