(a) Average sleep duration with respect to age and day of the week. Average sleep time across age groups was longest on Sunday followed by Saturday and was markedly shorter during the week, gradually decreasing from Monday to Friday for most age groups. (b and c) Average change in weekday (b) (Mon–Fri) and weekend (c) (Sat+Sun) waking activity time depending on sleep time category (N = 23,325) based on multiple linear regression models adjusting for age, gender, ethnicity, educational attainment, income, presence of partner, and presence of children. The 7.5 h to <8.5 h sleep time category served as a reference. For work time, separate models were run for the whole group (Work) and those only who worked on the interview day (Work>0 min). The largest reciprocal relationship to sleep was found for work time, followed by commute/travel time. Short sleepers spent more time socializing, relaxing, and engaging in leisure activities, while both short and long sleepers watched more television than the average sleeper. (Reprinted with permission from Basner et al., 2007.)

(a and c) Daily means (±SEM) of (a) MWT sleep onset latency and (c) PVT performance in the sleep restriction group (n = 142, 4 h TIB for five nights [SR1–SR5], solid line), and the control group (n = 17, 10 h TIB on all nights, dashed line). All subjects had 10 h TIB (22:00–08:00) on baseline day 2 (B2). Sleep restriction on SR1 to SR5 was from 04:00 to 08:00. Data are plotted to show deficits in neurobehavioral functions increasing (upward) on the ordinate. Relative to the control condition, sleep restriction degraded neurobehavioral function over days (decreased MWT sleep onset latency and increased PVT lapses [>500 ms reaction times]). (b and d) Daily means (±SEM) of (b) MWT sleep onset latency and (d) PVT performance following the acute recovery (REC) night as a function of increasing TIB dose (0–10 h, solid line), controlling for covariates (i.e., baseline, cumulative deficits during sleep restriction, age, and sex). Sleep-restricted subjects (n = 142) were randomized to either 0 h TIB (n = 13), 2 h TIB (n = 27), 4 h TIB (n = 29), 6 h TIB (n = 25), 8 h TIB (n = 21), or 10 h TIB (n = 27). For comparison, horizontal dotted lines show baseline night (B2, 10 h TIB) values, and horizontal dashed lines show control group (n = 17) means on day 8 (10 h TIB), which is the study day equivalent to REC. These neurobehavioral outcomes showed improvement as recovery sleep doses increased (MWT sleep onset latencies increased and PVT lapses decreased); however, even at the highest sleep recovery dose, functioning did not return to baseline or control condition levels. (Reprinted with permission from Banks et al., 2010.)

Neurobehavioral performance at baseline and during chronic partial sleep deprivation for the PER3 genotype groups. Mean (±SEM) (a) PVT lapses (>500 ms reaction times) per trial and (b) Karolinska Sleepiness Scale (KSS) scores at baseline (b) for each partial sleep restriction night (SR1–SR5) for PER34/4 (open circles), PER34/5 (gray triangles), and PER35/5 (closed circles) subjects. All genotypes demonstrated large but equivalent cumulative decreases in cognitive performance (PVT) and increases in sleepiness (KSS) across sleep restriction nights. As illustrated by increasing standard error bars in (a), interindividual differences in PVT lapses increased across sleep restriction nights in the entire study group (from Goel et al., 2009a).

Restriction of nocturnal sleep in healthy adults resulted in near-linear increases in PVT lapses (>500 ms reaction times) of attention across 14 days (coefficients of change near 1.0), but subjective ratings of sleepiness, measured using the Stanford Sleepiness Scale (SSS), showed a nonlinear coefficient below 0.5 for change over days. As objective performance continued to decline near-linearly, there were only minor further increases in the subjective ratings of sleepiness. By the end of the 14 days of sleep restriction, when PVT performance was at its worst levels, subjects in the 4 and 6-h sleep period conditions reported feeling only slightly sleepy. Therefore, unlike performance measures, sleepiness ratings appeared to show adaptation to sleep restriction (N = 35 subjects; 8 h condition n = 9, 6 h condition n = 13, and 4 h condition n = 13). (Reprinted with permission from Van Dongen et al., 2003.)