568 BRAIN MECHANISMS AND LEARNING 



one dot^ ill which the shock reinforcement was weak, and in one dog in which 

 avoidance technique was used (i.e. the stimuhis was not apphcd at all) disinhibition 

 was not observed, hi Figs, i and 3 the records of some typical experiments are 

 presented. 



After parietal ablations no changes occurred in either positive or inhibitory 

 CRs. 



Fig. 1 

 The extent of prefrontal and parietal (control) lesions in dogs. 

 The corte.x is shown in two dimensions. By dense stippling the usual prefrontal and parietal 

 ablations are shown. Sparse stippling denotes part of the premotor area involved in our 

 extensive prefrontal lesions. 



While limited ablations produce disinhibition, the extensive ones produce in addition 

 hyperactivity. 



When, after a prefrontal operation, inhibitory CSs are repeatedly applied with- 

 out reinforcement, inhibitory reflexes are gradually re-established, hi some cases 

 restoration occurs after only a few trials, while in others it takes a long time, and 

 may be incomplete. This depends chiefly on the difficulty of the inhibitory task for 

 a given dog and, perhaps, on the extent of its lesion. 



The impairment of inhibitory CRs after prefrontal lesions could be ascribed, of 

 course, to the animal's loss of discriminatory ability. But the fact that disinhibition 

 is, as a rule, only partial (which is best seen in salivary reflexes), and especially the 



