124 BRAIN MECHANISMS AND LEARNING 



bodily orientation, then they will go either in the other direction or will 

 not go anywhere. Of course they are also not able to go to the proper 

 food tray after receiving food on the starting platform, or after being 

 taken out of the room. When two signals are given, one after the other, 

 the dog after release, if not distracted, goes correctly to the last signalled 

 food tray and does not go to the other one. In other respects the general 

 behaviour of our prefrontal dogs does not differ from that before opera- 

 tion, in particular they do not display any hyperactivity or exaggerated 

 reactions to new stimuli. 



Our experimental data seem to support the original idea of Jacobsen 

 that the impairment of delayed responses in prefrontal animals is due to 

 the loss of recent memory. However, this statement requires one substan- 

 tial qualification, namely, that not all kinds of recent memory are impaired 

 after prefrontal lesions but only recent memory of directional cues. In fact 

 we have so far no evidence to show that other sorts of recent memory are 

 also affected by these lesions and we have already some evidence that it is 

 not so. One bit of it is provided by Mishkin and Pribram (1956) who 

 have found that delayed responses in simple go-no-go tests were not 

 impaired in prefrontal monkeys. Another one will be presented later. 



The important problem arises as to why it is that only the recent 

 memory of directional cues is destroyed after prefrontal lesions. We think 

 that a tentative answer to this question can be given. 



The extensive study made recently by Soltysik in our laboratory (in 

 preparation) concerning the effects of caudate lesions on delayed responses 

 revealed that these lesions produce striking disorciers of orienting reactions. 

 The animals either do not visibly pay any attention to the auditory stimuli, 

 or are not able to locate correctly the source of the stimulus even during 

 its operation. When after some time this deficit is compensated the 

 delayed responses are as much destroyed as in prefrontal animals. These 

 animals arc also severely impaired in all locomotor CRs, not being able to 

 find their way to the familiar places they ran to hundreds of times before 

 operation. 



Although premotor cortex was not specially studied from this point of 

 view, nevertheless as observed by I. Stg pien et al. (in preparation) premotor 

 lesions, and even more so premotor-prefrontal lesions, also produce 

 striking defects in the animal's orientation in space and orienting reactions. 

 The connections between caudate nucleus and pericruciate region were 

 emphasized by several authors (cf Purpura et al.). 



All these data show that both premotor area and the rostral part of 

 caudate nucleus play an important part in general orientation of animals in 



