Table 1.
Participant demographics.
Fig 1.
Time of day at the top is Chicago time, and time of day on the bottom is Kenyan time (9-h later than Chicago time). Study day is shown on the left. Black shading shows timing of scheduled sleep periods. Schedules were individualized for each participant to best match their habitual sleep times. This diagram shows the protocol for a participant on a 00:00–08:00 baseline sleep schedule. Days 1–4 were baseline during which participants remained on local, Chicago time (as indicated on the left). On days 6–9 the sleep schedule was shifted 9-h earlier (advanced) as though participants had traveled to Kenya, and the wall clocks in the bedrooms were changed to indicate the shifted, Kenyan time. During baseline days the sleep schedule was aligned with each participant’s circadian rhythms, whereas during advanced days the sleep schedule was misaligned. “X” shows the timing of the Automated Neuropsychological Assessment Metrics (ANAM) performance battery and “Px” shows the timing of practice ANAM tests. Tests were given relative to each participants scheduled sleep times; 2 h after waking, and then every 3 h with a total of 5 tests per day. Light grey shading shows the timing of circadian phase assessments, during which the dim light melatonin onset (DLMO) was assessed.
Fig 2.
Dim light melatonin onset (DLMO) and estimated temperature minimum (Tmin) for each participant.
DLMO was measured after the four baseline days on Chicago time (baseline/aligned) and after the three days on Kenya time (advanced/misaligned). Rectangles show the timing of the sleep/dark periods. Top: Circles show the DLMO relative to the baseline bedtime, with 0 representing the timing of the start of the scheduled baseline sleep period. Bottom: Triangles show the Tmin relative to baseline bedtime. The Tmin was calculated as the DLMO + 7 h. Filled symbols represent African-Americans and open symbols are European-Americans. The DLMOs and Tmins were properly aligned to the sleep/dark periods during baseline (DLMOs before sleep and Tmins within sleep), but were misaligned relative to the sleep/dark period during advanced days. The vertical symbol placement is for visualization purposes and has no relationship to days.
Fig 3.
Total Sleep Time (TST) and Columbia jet lag scale scores by study day.
TST was measured using sleep logs (top) and actigraphy (middle). Higher scores on the Columbia Jet Lag Scale (bottom) represent increased feelings of jet lag. Closed circles represent African-Americans and open circles represent European-Americans. N = 20 African-Americans, 17 European-Americans for sleep logs and Columbia jet lag scale. N = 15 African-Americans, 16 European-Americans for Actigraphy. Data are mean ± SEM. Baseline/aligned (days 2–4) and advanced/misaligned (days 6–8) were separated by a phase assessment day (refer to protocol, Fig 1). Asterisks denote significant differences (P ≤ 0.05) between African-Americans and European-Americans as determined by mixed model ANOVAs. There were no significant differences between African-Americans and European-Americans for Columbia Jet lag Scale scores, but there were significant differences for TST.
Table 2.
Main and interaction effects of ancestry and condition on sleep and cognitive performance.
Table 3.
Means for sleep and cognitive performance measures for ancestry and condition.
Fig 4.
Cognitive performance during baseline/aligned and advanced/misaligned days.
Performance was assessed on the simple reaction (RT) time task (A and B), procedural RT task (C), Go/No-Go task (D), and code substitution-delayed task (E). Closed circles represent African-Americans and open circles represent European-Americans. Dark grey shading represents timing of scheduled sleep/dark episodes during both baseline/aligned and advanced/misaligned days. Light grey shading on the right panels represents the previous baseline sleep episode. The first three cognitive performance tests (1, 4 and 7-h after baseline bedtime) during the advanced/misaligned days occurred when participants would normally be sleeping (i.e. during the scheduled baseline sleep/dark episode). Lapses (A) were defined as being RTs < 500ms, slow responses (C) were responses exceeding the 90th percentile of the cumulative distribution of each participant’s baseline responses, and d-Prime scores (D) were the discriminability values indicating the overall ability of to discriminate between the go and no-go stimuli. Higher scores for A, B, and C represent worse cognitive performance. Lower scores for D and E represent worse cognitive performance. N = 19 African-Americans and 17 European-Americans (A and B). N = 20 African-Americans and 17 European-Americans (C, D and E). Asterisks denote significant differences (P ≤ 0.05) between African-Americans and European-Americans at each hour after baseline bedtime as determined by mixed model ANOVAs. There were no statistically significant differences between African-Americans and European-Americans during baseline/aligned, but there were differences found during advanced/misaligned days (right panels), particularly at the time corresponding to the end of baseline sleep.
Fig 5.
Subjective sleepiness and fatigue (low energy level) during baseline/aligned and advanced/misaligned days.
Closed circles represent African-Americans and open circles represent European-Americans. Dark grey shading represents timing of scheduled sleep/dark episodes during both baseline and advanced days. Light grey shading on right panels (advanced) represents the previous baseline sleep/dark episodes. Top panel shows subjective ratings on the fatigue mood dimension (low energy level) and the bottom panel shows subjective sleepiness (Stanford Sleepiness Scale). Fatigue scores were on a scale of 0–6 and the Stanford Sleepiness Scale is a scale of 1–7. For both measures higher scores represent higher feelings of fatigue/sleepiness. N = 20 African-Americans and 17 European-Americans. Sleepiness and fatigue were higher during advanced/misaligned days compared to baseline/aligned days, but there were no significant differences between African-Americans and European-Americans for either measure at any time point.