EEG evolution of the different states of sleep in the kitten
1 . The evolution of cortical and muscular electrical activity during waking and the different states of sleep have been studied in kittens bearing electrodes chronically implanted in the cortex and in the neck muscles.
2. Three main periods can be distinguished for the EEG and behavior during this evolution:
(a) During the first week after birth the cortical activity does not change with the various states of vigilance. Nevertheless, observation of the behavior and polygraphic recordings makes it possible to differentiate two states of sleep: the first one is called "sleep with jerks" and is characterized by total disappearance of the EMG of the neck, slowing of the heart rate, jerks of the body and of the legs, and rapid eye movements. This state may follow directly the waking state and constitutes 40 to 50% of a recording session and about 90% of total behavioral sleep. The second is called "quiet sleep" and is inconstantly present. It has no muscular jerks.
(b) During the second week some EEG variation begins to appear. A fast cortical activity persists during the period of "sleep with jerks" while only very short phasic activation patterns are seen during behavioral arousal. During "quiet sleep" there are cortical spindles and the activity of the neck muscles seems to depend largely upon the sleep posture of the kitten.
(c) From the beginning of the third week onward, the two states of sleep are similar to those of the adult cat: there is a transition from "sleep with jerks" to paradoxical sleep and from "quiet sleep" to slow sleep with high voltage slow waves.
3. Studies of kittens decerebrated at birth show that the caudal part of the brain-stem is sufficient for the appearance of "sleep with jerks".
4. These results are discussed, together with the experimental results obtained in adult cats. They show that paradoxical sleep is qualitatively different from, and ontogenetically older than, slow sleep. Furthermore, it is probable that the neural structures which are responsible for the fast cortical activity during paradoxical sleep come into play sooner after birth than the neural structures responsible for cortical arousal during waking. Finally, the onset of the high voltage slow waves of slow sleep appears to be contemporaneous with the achievement of cortical maturation.
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