472 BRAIN MECHANISMS AND LEARNING 



electrical activity during the two stages of sleep were the same as in intact 

 animals. 



Mesencephalic cats (Fig. 6) : RostraUy (i.e. in front of the transsection), the 

 cortex and the diencephalon had the 'cerveau isole' type of electrical 

 activity with monotonous spindles and slow waves which might persist for 

 several days. 



Catidally (behind the transsection), the mesencephalic reticular formation 

 presented continuous fast activity and no slow wave or spindle could be 

 recorded. Only the paradoxical stage was present: rhythmic 'spindles' at 

 the rhombencephalic level during which the cat had a behavioural sleep 

 posture with complete atonia. This stage would thus appear as an 'archeo- 

 sleep' for a preparation which possessed only an archeo-encephalon 

 related to the external world. 



If the transsection of the brain stem was not total, slow waves were 

 recorded at the mesencephalic reticular formation and the patterns of 

 electrical activity during the two stages of sleep were usually similar to 

 those of the intact animal (Fig. 5). These facts lead to the following con- 

 clusions (Fig. 7) : 



Sta{ie I of sleep : 



Since the threshold of arousal was raised during the slow wave activity 

 in the reticular formation, this slow _activity must be inhibitory. Since no 

 slow activity could be recorded at the mesencephalic level in a totally 

 neodecorticated cat, or behind a total transsection of the brain stem, one 

 may conclude that the inhibitory slow waves arc a descending activity 

 and that they require, at least, the integrity of a small part of the cortex. 

 Thus, the first stage of sleep would appear to be the result of the activity 

 of some telencephalic inhibitory system acting upon the ascending 

 activating reticular system. 



Sta(^e 2 or paradoxical staqe: 



[a) Since the behavioural aspects of the paradoxical stage are the same in 

 intact, decorticated and mesencephalic cats, and since during this phase a 

 peculiar activity appears at the pontine reticular formation level, one may 

 conclude that this rhombencephalic region is directly related to this stage. 

 This structure appears to act caudally and suppresses totally the tonic 

 muscular activity. It is suggested that this effect could be mediated through 

 the supra spinal control of the Gamma system. 



{b) The appearance of a fast activity, at the mesodiencephahc and cortical 

 levels during this stage is paradoxical since the level of sleep is deeper than 

 in the first stage and not intermediary between sleep and waking. Such a 



