ANATOMICAL AND ELECTROGRAPHICAL ANALYSIS 

 OF TEMPORAL NEOCORTEX IN RELATION TO 

 VISUAL DISCRIMINATION LEARNING IN MONKEYS^ 



Kao Liang Chow 



Our knowledge of brain functions relating to behaviour has advanced 

 rapidly in recent years. One of the central issues in this area, that of the 

 neural mechanisms of memory and learning, however, remains experi- 

 mentally elusive. This problem may be approached from two directions. 

 One is to use a simple preparation, such as a protozoan or a synaptic 

 junction and to study any physictvchcmical changes resulting from 

 repeated excitation or exercise. The other is to use an animal with a well- 

 developed brain in which learning can be dehned behaviourally and to 

 analyse at a gross level the neural structures involved. There are difficulties 

 in both approaches. Thus, one wonders how to identify learning in the 

 simple organism and how to extrapolate from any mechanisms detected 

 there to a more complex brain. If one starts with the second type of 

 system, on the other hand, there is only hope but no guarantee that sucli 

 analysis will eventually reach the basic learning mechanisms at a neuronal 

 or molecular level. Also, it is not clear whether there are one or more 

 neural mechanisms underlying the various types oi learning tliat are 

 dehned behaviourally. 



The following material illustrates the second type of approach. The 

 neural correlates of learning and retaining visual problems have been 

 analysed at a gross level. In rhesus monkeys, the cortex of the middle and 

 inferior temporal gyri have been shown to be concerned with visual 

 discriminations (Chow and Hutt, 1953 ; Riopelle ct ai, 1953 ; IVibram and 

 Mishkin, 1955). After bilateral ablation of this cortical area, a monkey will 

 learn to choose one from a pair of visual stimuli (such as, red or green 

 colours, triangular or square patterns) in order to get food, but at a slower 

 rate than normal, unoperated annnals. Or, if a monkey has earlier learned 

 to solve these problems the forgetting produced by the surgical ablation 

 can be reversed by relearning. This detrimental effect is specific to the 

 temporal cortex; lesions in other neocortical areas do not affect visual 



' Studies reported m this paper were suppiirted by research grant B-801 (C3) trmn the 

 National histitute of Neurological Diseases and Blindness, National histitute of Health, and 

 the Wallace C. and Clara M. Abbott Memorial Fund of the University of Chicago. 



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