510 



BRAIN MECHANISMS AND LEARNING 



used. Thirty trials were given each day, until a criterion of 90 per cent 

 correct responses in a one-day session was reached. The animals were then 

 subjected to bilateral one-stage operation. Fourteen days later they were 

 tested for retention of these visual discriminations. 



The brains of all animals were examined histologically, and the lesions 

 reconstructed. Fig. i is of the reconstruction of a brain with both para- 

 striate and pulvinar ablations. The cortical lesion was not complete, but 

 the posterior part of n. pulvinaris mcdialis was largely removed. A second 

 monkey had similar lesions. The cortical regions subjected to the other 



Tablh I 



PRE- AND POST-OPERATIVE LEARNING SCORE OP MONKEYS WITH DIFFERENT 



TYPES OF TEMPORAL NEOCORTICAL OPERATIONS. NUMBER OF TRIALS TO 



CRITERION, EXCLUDING CRITERION TRIALS. NUMBERS IN ITALICS, LACK OF 



POST-OPERATIVE RETENTION 



three types of surgery (ablation, cross-hatching, undercutting) were all 

 restricted to the middle and inferior temporal gyri rostral to the vein of 

 Labbc. The locus and size of the lesion in individual monkeys showed 

 minor variations. Retrograde degeneration appeared only in the posterior 

 part of n. pulvinaris medialis. In general, the cortex above the plane of 

 undercutting showed no damage. The subpial vertical hatching cut 

 beyond the thickness of the cortex, invading to some extent the underlying 

 white matter. The cortex between the cuts seemed to be normal in 

 appearance. 



