NON-SENSORY EFFECTS OF FRONTAL LESIONS ON 

 DISCRIMINATION LEARNING AND PERFORMANCE 



H. Enger Rosvold and Mortimer Mishkin 



In his recent Salmon Lectures, Magoun (1958) has described how even 

 the Ancients had formiUated theories of brain-behaviour relationships. 

 To them it appeared that sensory, associative and motor faculties were 

 served by clearly separated parts of the brain each of which was uniquely 

 organized for its specific function. Conceptions of brain organization have 

 progressed through a variety of formulations, but at each stage there have 

 been those who were ready to defend this ancient conception of a cerebral 

 localization of function. Thus, at widely separated times, Ferrier (1875), 

 Bianchi {192.2} and Jacobsen (193 s) have contended that the most anterior 

 cerebral structure, the prefrontal lobes, was an 'association' area con- 

 cerned with complex, non-sensory functions clearly distinguishable from 

 the sensory functions served by posterior cortex. Recently, however, 

 studies such as those of Woolsey (1958), Neff and Diamond (1958), 

 Rose and Woolsey (1958) and Lilly (1958) have shown that the neural 

 representation of sensory functions encroach upon 'association' cortex, 

 suggesting that the prefrontal lobes may be involved in sensory processes 

 after all. It is appropriate, therefore, to take a new look at the behavioural 

 evidence related to this problem. 



For the most part experimental studies concerned with frontal lobe 

 function have emphasized the severe effects of damaging this structure on 

 performance of delayed-response tests. Furthermore, the results have 

 clearly supported the view that impairment on this type of problem is 

 uniquely associated with frontal as opposed to posterior cortical lesions 

 (Blum, Chow and Pribram, 1950; Meyer, Harlow and Settlage, 195 1). 

 Finally, and most important in connection with the present problem, in 

 emphasizing the specific nature of this frontal-lobe deficit, investigators 

 since Jacobsen (1935) have contrasted it sharply with the absence of 

 deficit on sensory discrimination tasks. Impairment on discrimination tasks 

 has, instead, been reserved for the effects of posterior lesions. 



Unfortunately, however, this enthusiasm to dissociate delayed response 

 and sensory discrimination functions has resulted in the neglect of impor- 

 tant contradictory evidence. For example, Pribram, Mishkin, Rosvold and 

 Kaplan (1952) did not deal with the fact shown in the right of Fig. i that 



555 



