430 BRAIN MECHANISMS AND LEARNING 



reticular response almost disappears. If one then briefly tetanizes the midbrain 

 recording electrode the response returns almost to its original size and behaves in 

 much the fashion of a post-betanic potentiation, with gradual decay to a low level 

 over 10 to 15 minutes. This potentiation can be repeated indefinitely. These 

 animals have certain curious behavioural alterations which may be classified as 

 catatonic. They suifer a gross defect in avoidance behaviour, but in this respect tend 

 to recover over a period of months, although they never revert to normal. They 

 assume these curious postures even though they are apparently alert and in many 

 cases do not feed spontaneously. Now on the basis of these findings, we would 

 suggest that cither arising in the subthalamus, or passing through it, there arc 

 certain tonic facilitatory influences which are mainly responsible for the normal 

 accessibility ot reticular units to input from the periphery. We also have evidence 

 that there is a brief phasic inhibitory aspect to this activity, much as Huguelin and 

 Bonvallet have described but the overall effect ot subthalamic lesions of the type 

 we have described is a loss of a tonic facilitation. 



Palestini. We have postulated in this paper that EEG activation patterns and 

 facilitation of visual cortical responses appear when bulbo-pontine structures are 

 left out of action by the section. But we have also pointed to possible inhibitory 

 and synchronizing influences originated in higher levels, hi relation to facilitating 

 mechanisms acting upon reticular formation and coming from upper segments we 

 had only considered corticoreticular relationships. Now Dr Adey has presented us 

 a new possibility of facilitating influences which seems quite important to us. 



Olds. I would like to address myself to Dr Adcy's material, to ask whether there 

 was any particular part of the reticular formation in which recording electrodes 

 should be placed in order for this eifect to be obtained. I would say that the area he 

 describes as having his lesion is very similar to regions where we get very rapid 

 self stimulation and I am just wondering if the part of the tegmentum used for 

 recording is also the part that gives us very rapid self-stimulation which would be 

 the vcntro-latcral part of the tegmentum. 



Adey. First of all, the recordings were all made in the paramedian part of the 

 dorsal reticular formation adjoining the peri-aqueductal grey-matter at the 

 rostral mesencephalic level. As far as the subthalamic lesions goes, it is my impres- 

 sion that it is a region very heavily traversed by a rhinonccphalic descending flux 

 which arises from the pyriform cortex, the amygdala. It is also the main descending 

 area for fluxes through the corpus striatum and particularly from the globus 

 pallidus. We have not looked specifically in the ventro-lateral tegmentum. 



Galambos. As Dr Adey has said, the main outflow region of the limbic system 

 is to this midbrain reticular formation. I am not exactly clear where the prctri- 

 geminal section cuts through the midbrain but wonder whether it might destroy 

 the caudal part of the nucleus of Bechtercw which is a specific midbrain terminus 

 for the limbic outflow. As I understand Dr Palestini's view, he interprets the lack 

 of habituation of the visual cortical response after the lesion to absence of impulses 

 from regions caudal to the cut. Could it be that his lesion destroys a part of the 

 nucleus of Bechterew and thus prevents inflow to the midbrain from the limbic 

 structures more rostrally located? 



Palestini. Prctrigeminal transection is made at a midpontine level and leaves 

 intact the anterior part of the pons and midbrain structures. Previous research has 

 given some data about the possible importance of nucleus pontis oralis in the 



