Phase advance of the LD cycle alters the distribution but not the total amount of sleep.

<p>A single cohort (<i>n</i> = 8) of adult male mice were entrained to a 12∶12 LD cycle for 2 weeks. The mice were videotaped for 24 hrs to establish a baseline and an additional 48 hr during which the mice were subjected to a 6 hr phase shift of the LD cycle. The video was scored every 5 min to determine if the mice were awake or asleep. In both <b>A</b> and <b>B</b>, the significant differences between baseline and the first day of the phase shift as determined by 2RM ANOVA with post-hoc Bonferroni's <i>t</i>-tests are denoted by “*” and the significant differences between baseline and the second day of the phase shift by “†”. <b>A</b>) A 6 h phase advance of the LD cycle did not change the total amount of sleep over a 24 h cycle compared to the baseline recordings, but resulted in minor changes in the distribution of sleep. <b>B</b>) A 6 h phase delay of the LD cycle resulted in increased sleep during and after the phase shift, and caused an immediate increase in sleep during the extended 6 h of light, as well as a corresponding decrease in sleep during the dark hours of the following day.