Figure 8 : Diagram of the postnatal development of the states of sleep
in the kitten
(Based on three-hour recordings daily.) Stippled: Wakefulness. Vertical
hatching: Slow sleep with nuchal EMG activity. Crossed area: Slow sleep
without tonic muscular activity. Diagonal hatching: P.S. The limit between
the vertical white columns and the continuous marking represents the age
at which cortical activity takes on the appearance seen in adulthood.
Abscissa: Relative proportion (%) of each state. Ordinate: Age in days.
From Valatx et al., 1964.
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