KAO LIANG CHOW 51 1 



Tabic I summarizes the results. The numbers of trials to criterion 

 (excluding the criterion trials) in pre-opcrative learning and post-operative 

 testing of all monkeys are included. The numbers ni italics indicate that 

 after operation the animal did not retain but relearned a specific discrim- 

 ination. It is clear that, beside a few exceptional cases, only cross-hatching 

 lesion produced an effect resembling that of ablating the temporal cortex. 

 Animals with either the combined parastriate and pulvinar lesion or with 

 the undercutting showed good retention ; the degree of saving is com- 

 parable to that of normal animals (Chow, 1958). Thus, whatever the 

 neural mechanisms are involved, the interchange of information between 

 the visual and temporal areas for the discriminations used depends 

 primarily on cortico-cortical pathways. 



The present results may be compared with those of studies by Sperry. 

 He found no motor defects after cross-hatching the sensorimotor 

 cortex in monkeys when the cuts did not penetrate beyond the depth of 

 the cortex (Sperry, 1947). Also, cats showed a normal rate of learning and 

 good retention of visual discriminations after multiple subpial cuts of the 

 visual area (Sperry, Minor and Myers, 1955). Different neural organiza- 

 tions between the primary projection areas and the association areas may 

 be implicated to account for the different results. 



ISOLATED TEMPORAL AND VISUAL CORTICES 



One of the inherent weaknesses of using the ablation method is that 

 one removes the structure to be studied. A more rational way of studying 

 the function of a cortical area is to leave this region intact, but to remove 

 all other cortex. To study the role of the temporal cortex in visual learn- 

 ing, one needs a decorticated monkey with sparing of only the temporal 

 and visual areas. A series of behaviourally testable monkeys was prepared 

 which more or less met this requirement. The animals were subjected to 

 three separate operations with long recovery and training periods between. 

 The first operative stage was used to cut one optic tract (left side), the 

 corpus callosum, the hippocampal commissure, and to ablate one tem- 

 poral cortex (left side). Extensive decortication of the contralateral (right) 

 side, sparing the temporal and visual areas, was done during the second 

 operation. The orbital and medial cortical tissue and the retrosplenial area 

 were variably preserved. Monkeys after this second operation were 

 suitable for studying the visual function of the temporal cortex in isola- 

 tion. The third operation was performed to remove the remaining tem- 

 poral cortex (right side). Such a monkey had by and large only one visual 

 area to deal with visual tasks. 



