STUDIES OF CEREBRAL FUNCTION IN LEARNING 267 



learned, but in some cases training was continued for from 30 to 60 

 additional trials, as it was not always convenient to operate earlier. 

 Since I have found that over-training up to 1,400 trials does not 

 influence cortical localization, this additional training is not objection- 

 able. When the problem was learned the animals were subjected to 

 operation and their retention of the habit was tested as soon as their 

 physical condition permitted. 



In training ten trials were given daily. When the animal entered 

 the darkened alley he was punished and the trial was recorded as an 

 error, although he was allowed to turn back and pass through the 

 illuminated alley to the food. In the retention tests the same 

 method was used except that the animals were not punished. In 

 the records given below the number of errors made in each successive 

 ten trials of training and of the retention tests is given. Five errors are 

 to be expected from chance if the animal is not discriminating. Fewer 

 than four errors in ten trials suggest discrimination, and no error in thirty 

 consecutive trials usually means that the animal will discriminate 

 accurately thereafter. The individual records of the animals follow. 



No. 20. Large male. — Trained in visual discrimination. Sixty trials were 

 required for learning, with errors in successive tens of trials distributed as 

 follows : — 



7:6:2:5:3:2:0:0:0:0:0:0. 



The frontal lobes were transected and the caudate nuclei cauterized. The 

 animal was first tested three days after the operation. He was slow and 

 spastic, but made no error in twenty consecutive trials. For the next three 

 days he was in an excited state and showed great fear, either refusing to run 

 or dashing through the training box at random and paying no attention to the 

 food. On the eighth day he was again normal in behaviour and gave clear 

 evidence of discrimination. 



Post-operative retention tests ; errors in successive tens of trials on con- 

 secutive days after operation : — 



0:0: (frightened, 6 : 4 : 3) : 1 : : 1 : : 0. 



Extent of lesions (fig. 8). — Eight hemisphere : the lesion includes all of 

 the cortex of the dorsal convexity from the level of the thalamus to the base 

 of the olfactory bulb. It extends over the orbital surface at the level of the 

 caudate nucleus where the cautery passed through the external capsule. The 

 caudate nucleus is destroyed from the level of the anterior commissure to its 

 posterior limit. There is some injury to the anterior thalamic nuclei. Left 

 hemisphere : the lesion to the cortex is similar to that on the right, but does 

 not extend on the orbital surface. The injury to the caudate and thalamic 

 nuclei is similar to that on the right. 



This animal showed unmistakable evidence of retention after 



