556 



BRAIN MECHANISMS AND LEARNING 



their frontal animals were significantly inferior to normals in retention of 

 a visual discrimination habit. ^ They emphasized, instead, that their animals 

 showed some savings in relearning the habit (the left of Fig. i), and used 

 these data to support the thesis put forth earlier byjacobsen (1935) that 

 frontal lesions leave discrimination functions unimpaired. In defending 

 Jacobsen's thesis they were ignoring not only their own results, but also a 

 nimiber of other reports in the intervening 20 years which had clearly 

 implicated frontal cortex in discrimination learning and retention. In 



VISUAL DISCRIMINATION RETENTION 



300- 



S 150 



PRE POST 



30 



(T 15 



N— 3 



(PRIBRAM, ROSVOLD.MISHKIN, a KAPLAN, 1952 ) 



Fig. I 

 Effects of frontal lesions on visual discrimination retention. 



1940, for example, Allen had demonstrated that dogs with pre- 

 frontal lobectomies were unable to learn to discriminate olfactory stimuli. 

 In 1943, Harlow and Dagnon had shown that monkeys with 

 prefrontal lobectomies were impaired in learning even simple discrimina- 

 tions in vision. And again in 1952, Blum had shown that prefrontal 

 monkeys were deficient in auditory discrimination learning. Surely, such 

 evidence demonstrating impairment after frontal lesions in all sensory 



^ This and the following figures arc derived from the data appearing in the reports of the 

 authors indicated. In all figures, operated and control groups of monkeys are denoted as 

 follows: F — Frontal, N — Normal, P — Parietal, PT — Posterior Temporal, T — Temporal. 

 A number below the bar graph denotes the number cif monkeys in the group. 



