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. 2016 Mar 28;11(3):e0151770.
doi: 10.1371/journal.pone.0151770. eCollection 2016.

Prediction of Vigilant Attention and Cognitive Performance Using Self-Reported Alertness, Circadian Phase, Hours since Awakening, and Accumulated Sleep Loss

Eduardo B Bermudez  1 , Elizabeth B Klerman  2 , Charles A Czeisler  2 , Daniel A Cohen  3 , James K Wyatt  4 , Andrew J K Phillips  2
Affiliations

Prediction of Vigilant Attention and Cognitive Performance Using Self-Reported Alertness, Circadian Phase, Hours since Awakening, and Accumulated Sleep Loss

Eduardo B Bermudez et al. PLoS One. .

Abstract

Sleep restriction causes impaired cognitive performance that can result in adverse consequences in many occupational settings. Individuals may rely on self-perceived alertness to decide if they are able to adequately perform a task. It is therefore important to determine the relationship between an individual's self-assessed alertness and their objective performance, and how this relationship depends on circadian phase, hours since awakening, and cumulative lost hours of sleep. Healthy young adults (aged 18-34) completed an inpatient schedule that included forced desynchrony of sleep/wake and circadian rhythms with twelve 42.85-hour "days" and either a 1:2 (n = 8) or 1:3.3 (n = 9) ratio of sleep-opportunity:enforced-wakefulness. We investigated whether subjective alertness (visual analog scale), circadian phase (melatonin), hours since awakening, and cumulative sleep loss could predict objective performance on the Psychomotor Vigilance Task (PVT), an Addition/Calculation Test (ADD) and the Digit Symbol Substitution Test (DSST). Mathematical models that allowed nonlinear interactions between explanatory variables were evaluated using the Akaike Information Criterion (AIC). Subjective alertness was the single best predictor of PVT, ADD, and DSST performance. Subjective alertness alone, however, was not an accurate predictor of PVT performance. The best AIC scores for PVT and DSST were achieved when all explanatory variables were included in the model. The best AIC score for ADD was achieved with circadian phase and subjective alertness variables. We conclude that subjective alertness alone is a weak predictor of objective vigilant or cognitive performance. Predictions can, however, be improved by knowing an individual's circadian phase, current wake duration, and cumulative sleep loss.

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Conflict of interest statement

Competing Interests: The authors of this manuscript have the following competing interests: Dr. Klerman has received travel funds from Servier and the Sleep Technology Council. Dr. Phillips has consulted for Zeo, Inc. Dr. Wyatt has consulted for Phillips-Respironics. Dr. Czeisler has received consulting fees from: Amazon.com, Inc.; A2Z Development Center; Bose Corporation; Boston Celtics; Boston Red Sox; Cephalon, Inc.; Citgo Inc.; Cleveland Browns; Columbia River Bar Pilots; Jazz Pharmaceuticals; Koninklijke Philips Electronics, N.V.; Minnesota Timberwolves; Portland Trail Blazers; Samsung Electronics; Teva Pharmaceuticals; Valero Inc.; Vanda Pharmaceuticals. Dr. Czeisler has also received education/research support from Mary Ann & Stanley Snider via Combined Jewish Philanthropies, Philips Respironics, San Francisco Bar Pilots, and Vanda Pharmaceuticals, Inc. Dr. Czeisler is the incumbent of an endowed professorship provided to Harvard University by Cephalon, Inc. and holds a number of process patents in the field of sleep/circadian rhythms. Since 1985, Dr. Czeisler has also served as an expert on various legal cases related to sleep and/or circadian rhythms including those involving the following commercial entities: Bombardier, Inc.; Continental Airlines; FedEx; Greyhound; Purdue Pharma, L.P.; and United Parcel Service (UPS). Dr. Czeisler owns or owned an equity interest in Somnus Therapeutics, Inc. and Vanda Pharmaceuticals. He received royalties from Houghton Mifflin Harcourt/Penguin Press, and Philips Respironics, Inc. for the Actiwatch-2 and Actiwatch-Spectrum devices. Dr. Czeisler’s interests were reviewed and managed by Brigham and Women’s Hospital and Partners HealthCare in accordance with their conflict of interest policies. There are no patents, products in development or marketed products to declare. This does not alter the authors' adherence to PLOS ONE policies on sharing data and materials.

Figures

Fig 1
Fig 1. Changes in Sleep Debt by hour across the 3-week (twelve 42.85-h “days”) Forced Desynchrony protocol.
Sleep Debt in the Control group varies around zero hours due to prolonged wake and sleep bouts with a 1:2 sleep:wake ratio. The Chronic Sleep Restriction (CSR) protocol accumulates Sleep Debt across the entire duration of the protocol. Heavy lines indicate when the sleep was scheduled.
Fig 2
Fig 2. PVT scores by Circadian Phase and Wake Duration.
Mean reaction times (RT) on the Psychomotor Vigilance Task (PVT) are plotted as a function of Circadian Phase (zero degrees is the fit melatonin maximum) and Wake Duration (hours elapsed in scheduled wake episode). The top panel contains data from the Chronic Sleep Restriction (CSR) condition. The bottom panel contains data from the Control condition. Each column shows one week (four 42.85-h “days”) of data.
Fig 3
Fig 3. Subjective Alertness scores by Circadian Phase and Wake Duration.
Mean Subjective Alertness scores are plotted as a function of Circadian Phase (zero degrees is the fit melatonin maximum) and Wake Duration (hours elapsed in scheduled wake episode). The top panel contains data from the Chronic Sleep Restriction (CSR) condition. The bottom panel contains data from the Control condition. Each column shows one week (four 42.85-h “days”) of data.
Fig 4
Fig 4. The relationship between PVT standard deviation and PVT mean.
Data are shown for Chronic Sleep Restriction (CSR) and Control conditions. Data from both conditions demonstrate a robust relationship between the standard deviation and mean of the Psychomotor Vigilance Task (PVT). Logarithms of each variables are plotted to the wide ranges that the data span. Each data point represents one 10-min session. The same polynomial fit is shown to data in both plots with 95% confidence intervals indicated by dashed lines.
Fig 5
Fig 5. PVT standard deviation versus PVT mean for each participant.
The same data as in Fig 4 are plotted separately for each participant. Polynomial fits are shown with fixed effects (solid black line) and with mixed effects (dashed line).
Fig 6
Fig 6. PVT mean vs. Subjective Alertness.
Data are shown for Chronic Sleep Restriction (CSR) and Control conditions. Individual data points represent Subjective Alertness and mean Psychomotor Vigilance Task (PVT) responses from the same individual, paired by close timing in the same testing session. A single logistic function is fit to all data (solid line), with 95% confidence intervals of the best-fit line indicated by dashed lines.
Fig 7
Fig 7. PVT mean vs. Subjective Alertness for each participant.
The same data as in Fig 6 are plotted separately for each participant. Logistic fits are shown with fixed effects (solid black line) and with mixed effects (dashed line).
Fig 8
Fig 8. Comparison of model predictions of PVT mean relative to actual performance in each individual.
For each participant, we show a box-plot of the differences between predicted Psychomotor Vigilance Task (PVT) mean in each 10-min session and actual PVT mean. Outliers are shown as dots. The model that includes all four variables is used for predictions. Participants 1–9 are from the Chronic Sleep Restriction (CSR) condition. Participants 10–17 are from the Control condition.
Fig 9
Fig 9
Top Row (A) Actual PVT mean for the experimental data vs. Phase and Sleep Debt. Bottom Row (B) Predicted PVT mean from model vs. Phase and Sleep Debt. Plots show the mean reaction time (RT) on the Psychomotor Vigilance Task (PVT) as a function of Circadian Phase (zero degrees is the fit melatonin maximum) and Sleep Debt (cumulative hours of insufficient sleep opportunity). Left column values are taken during “Optimal Time” (defined as hours 2–10 after awakening). Right column values are taken during “Adverse Time” (defined as hours 20–28 after awakening).
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