408 BRAIN MECHANISMS AND LEARNING 



certain aspects of conditioning and learning in general. The integrity of 

 the cortex for complex discriminations is as important as the integrity of 

 subcortical structures for some of the simplest types of learning (habituation 

 and earliest manifestations of conditioning). Therefore, all the levels of the 

 central nervous system appear to be endowed with plastic properties which 

 cannot be ascribed exclusively to any particular locus of the brain. 



GROUP DISCUSSION 



Doty. I completely agree with Dr Hcrnandez-Pcon with regard to the excep- 

 tional importance of subcortical mechanisms in the establishment and performance 

 of conditioned responses. 



We can offer some additional experimental support (Doty, Beck and Kooi, 

 1959) for his position. Fig. i shows extensive brain stem lesions totalling 100 



A- 8.5 



Fig. 



Lesions in the central dicnccphalon, represented on plates from the stereotaxic atlas of Jasper 

 and Ajmone-Marsan (1954). See text. (From Doty, R. W., Beck, E. C. and Kooi, K. A., 

 1959. Effect of brain stem lesions on conditioned responses of cats. Experitneiital Neurology, 

 I, 360). 



mm.^ anterior, however, to the mesencephalon. This animal gradually recovered 

 from a cataleptic stupor during the first two post-operative weeks, and Fig. 2 

 shows that the EEG ultimately returned to normal levels. The animal walked after 

 the third week and would blink to a visually presented threat. No other conditioned 

 reactions could be observed post-operatively. Prior to surgery this cat made 

 discrete, conditioned flexions of a leg 80 per cent of the time to a tonal CS and 



