These results enable us to dissociate the two phases of sleep which are
relatively independent of one another. The EEG tracing of decorticate
or mesencephalic cats shows no slow phase whereas periods of "rhombencephalic
sleep" persist. In the cats with a pontile R.F. lesion, on the other hand,
only the phase of "slow sleep" appears, without any p.p. These facts lead
us to accept the intervention of two different systems during physiological
sleep in the cat.
(1) The first system appears to intervene during " spindles and
slow waves" sleep in the intact animal. It requires the presence of the
neocortex which is responsible for the slow activity. This corticifugal
slow activity expresses an inhibition phenomenon since the arousal threshold
produced by direct stimulation of the reticular formation rises during
this stage. This phase may there fore be described as telencephalic sleep.
It is possible that this telencephalic stage may represent a stage which
is acquired during telencephalization and that it could be described as
(2) The phase of "rapid" sleep- (paradoxical phase) which we propose
to call the "rhombencephalic phase" is dependent upon a totally different
system, situated at the level of the pontile reticular formation. It controls,
through the inhibitory R.F., the somato-vegetative phenomena (disappearance
of all muscular tonic activity even in the cases of decerebration or decerebellation
hypertony, variation in respiratory and cardiac rhythms). The rapid cortical
activity which accompanies this phase is not suppressed by the interruption
of the activating reticular system. This phase of sleep which only exists
in mesencephalic or pontile cats could be likened to an "archisleep".
This phase is more profound than the first one as the threshold of awakening
is increased in comparison with that of the slow wave phase of sleep.
Finally, it can be triggered off in animals by stimulating the lower part
of the brain stem, and it is suggested that this phase depends upon a