Table 2.

Period of Circadian Rhythms for Wakefulness at P21.5.

	Period (h)
≈12 h	12.17 ± 0.10
≈24 h	24.44 ± 0.12
24/12	2.01 ± 0.02

Circadian period length (± SEM; n = 5) at P21.5 significantly deviated from 24.0 h (t test, p = .024). The period length of the 24-h component was twice that of the 12-h component (24/12) and the 24/12-ratio did not significantly deviate from 2.0 (paired t test, p = .64). P21.5 was chosen because by then significant periodicity was established for all states and rats.