M. PALESTINI AND W. LIFSCHITZ 429 



tion or need a period at least three times longer than that required by the 

 normal animal to show it. Much more evident, in this respect, arc the 

 results obtained on secondary cortical potentials, since they show rapid 

 habituation in the normal cat. 



3. A significant increase in the primary and secondary cortical potentials 

 evoked by a luminous stimulus. Evidently the reactions described in 

 points 2 and 3 only refer to photic cortical responses ; this does not allow 

 us to extend them to other sensory responses. 



Aware of the oversimplification of our hypothesis and admitting that 

 other structures of the nervous system also participate, we would ascribe 

 different functions to two areas of the reticular formation. The influences 

 originated rostral to the midpontine level would mainly participate in 

 cortical dcsynchronization, in the facilitation of evoked potentials, in 

 dishabituation and in attention, while those originated caudal to this level 

 would synchronize the EEG, facilitate habituation and inhibit evoked 

 cortical potentials. These three influences ascribed to the reticular forma- 

 tion of the medulla lead us to think that this structure should be regarded 

 as an important part of a sleep system. 



GROUP DISCUSSION 



Adey. I would like to discuss a few aspects of the study that Mr Lindslcy and I 

 have undertaken to assess the role of subthalamic areas in the maintenance ot 

 reticular excitability, and I think these findings bear very closely on the papers that 

 have been presented this afternoon. These lesions are in chronic cats and monkeys 

 and they involve the subthalamus, the dorsal part of the hypothalamus and 

 frequently the ventro-mcdial part of the thalamus. These are chronic lesions and 

 the cats were kept in good condition for 6 weeks to 2 months before they were used 

 for subsequent acute or chronic experiments. It was found that, after such a lesion, 

 when recording from the medial reticular formation of the rostral mesencephalon, 

 many of the units which are normally present and respond to stimulation of 

 sciatic nerve are no longer active, and in fact it is very difficult to find spontaneously 

 firing units. When one is detected, it fires only slowly, and exhibits only a brief 

 phasic rise in firing rate with each stimulus, in contrast to the tonic and sustained 

 rise in firing rate induced in normal reticular units by repetitive sciatic stimulation 

 in most cases. Since it is almost impossible to assess reticular function on the basis of 

 such unit studies, we reverted to macro-electrode recordings in the rostral mid- 

 brain reticular formation adjacent to the periaqueductal grey matter. After brief 

 tctanization of the mid-brain recording electrodes for 2 or 3 seconds, there is a 

 slight facilitation of the reticular response to sciatic stimulation as compared with 

 the control records, lasting 5 to 10 minutes. After unilateral coagulation of the 

 subthalamus there is slight reduction in the reticular responses, when compared 

 with control records, but not very much. However, after bilateral coagulation the 



