THE INTRINSIC SYSTEMS OF THE FOREBRAIN 



1337 



formance ol delayed reaction and of alternation by 

 subhuman primates. These problems are usually 

 classified with those used primarily to study differen- 

 tiative behavior, although differences between the 

 two are recognized. These differences have been con- 

 ceptualized in terms of one-trial learning (99), im- 

 mediate memory (56) and retroactive inhibition (83), 

 conceptions which are insufficiently distinctive to 

 account for recently reported experimental findings 

 (94). More penetrating analyses have been accom- 

 plished for the effects of frontal intrinsic sector lesions 

 on the performance of the double alternation problem 

 (78) and for the simple alternation problem per se 

 (6a). These analyses emphasize the recurrent regu- 

 larities which constitute the alternation problems and 

 suggest that such problems be considered examples of 

 a larger class which can be distinguished from prob- 

 lems that require differentiation (37). Delayed reac- 

 tion may also belong to the class of problems specified 

 by recurring regularities; the recurrence, at the time 

 response is permitted, of some of the events present in 

 the predelay situation, constitutes an essential aspect 

 of the delay problem {94). 



The reasons for classifying the delayed reaction and 

 alternation problems with those related to systematic 

 \ariations of outcomes remain somewhat obscure. 

 The results of the following experiment provide some 

 clarification. Under special conditions, monkeys with 

 lesions of the frontal intrinsic sectors perform re- 

 markably well the delayed reaction and alternation 

 problems (93, 94). Adequate performance is estab- 

 lished, however, at the cost of a great number of 

 repetitive errors (though not of initial errors), as 

 shown in figure 14. These results can be described as 

 a failure in performance due to the relative inefficacy 

 of the outcome of the frontally operated animals" 

 actions in determining subsequent action. This de- 

 scription is compatible with the finding that, in de- 

 layed reaction, the important determinant of per- 

 formance is the outcome of the animal's reaction in 

 the predelay situation (94), the outcome having 

 'acquired distinctiveness" during the earlier phases of 

 the experiment. 



MODEL OF FRONTAL INTRINSIC MECHANISM 



From these data, a formal model of the neural 

 mechanism that underlies the effect of frontal in- 

 trinsic sector resections of intentional behavior can be 

 propo.sed. This model takes into account the neural 

 relationship between the frontal intrinsic sector and 



FIG. 14. Graph showing the differences in the number 

 of repetitive errors made by groups of monkeys in a 'go-no-go' 

 type of delayed reaction experiment. Especially during the 

 initial trials, frontally operated animals repeatedly return to 

 the food well after exposure to the 'nonrewarded' predelay 

 cue. Note, however, this variation of the delay problem is 

 mastered easily by the frontally operated group. The 12 

 rhesus monkeys used in the multiple object experiment (figs. 

 6 to II) served as subjects some 2 years earlier in the delayed 

 response experiment portrayed here. (Dr. Margaret Varley 

 assisted in the performance of the earlier experiment. ) 



the mediobasal structures of the forebrain (iio) and 

 is based on the finding that two classes of variables 

 determine the effects of an outcome of an action. A 

 large body of data has been accumulated in the last 

 20 years as a result of studies which made use of surgi- 

 cal ablation and electrical stimulation. These data 

 demonstrate the special relation of the mediobasal 

 systems of the forebrain to the class of variables sub- 

 sumed under the rubric 'disposition.' 



Mediobasal Forebrain and Disposition 



Changes in the following types of behavior are re- 

 ported to result from mediobasal forebrain ablations 

 and stimulations: fighting (dominance, reaction to 

 frustration); fleeing (escape and avoidance); feeding 

 (appetitive, such as hoarding, and consummatory) ; 

 and mating and maternal (nest building and care of 

 the young). Stimulation or ablation which affects one 

 of these behavior patterns is likely also to affect the 

 others (though not necessarily to the same extent). 

 On the other hand, the performance of discrimination 

 tasks remains unaffected (107). 



