Cognitive performance evaluation based on physiological indicators in different sleep restrictions

Working overtime in the night has become common due to escalating competitions. During the nighttime overwork, biomarkers such as the melatonin and cortisol, as well as the electrocardiogram (ECG) feature like heart rate variability (HRV), have been reported to be closely corelated with cognitive performances of people. However, their quantitative relationships with cognitive performances remain to be further clarified. To explore the patterns of human cognitive performances under different sleep-restrictions, three different sleep-restriction conditions were devised, including the mild restriction from 23:00 to 1:20 a.m., the moderate sleep-restriction from 23:00 to 2:30 a.m., and the severe sleep-restriction from 23:00 to 3:40 a.m. The experiment was conducted in an environmental chamber with the dimensions of 5000x3000 x2600 mm (LxWxH). The thermoneutral environment had the air temperature of 24°C and the relative humidity of 55%. During these sleep restrictions, the Deary-Liewald task, Stroop task, and Corsi block task were administered continuously to simulate the stable cognitive loads during overtime work. The overall performance index (OPI) was calculated from results of these tasks. Meanwhile, saliva melatonin and cortisol were collected during sleep restrictions, and ECG data were continuously recorded for HRV analysis. Results showed that the melatonin concentration during these three sleep restrictions elevated by 6.07 pg/mL (p<0.05), 7.17 pg/mL (p<0.05), and 7.7 pg/mL(p<0.05), respectively. SampEn kept reducing during all sleep restrictions, by 0.14 (p<0.05), 0.11 (p<0.05), and 0.15 (p<0.05), respectively. Mean heart rate (Mean HR) also reduced across all sleep restrictions, with the decrement of 5.88 (p<0.05), 9.94 (p<0.05), and 9.79 (p<0.05), respectively. Furthermore, the overall cognitive performances reduced generally with several fluctuations during all three sleep restrictions. Correlation analysis results indicated that the overall cognitive performance was positively correlated with mean heart rate (HR) (p=0.87, p<0.05), but negatively correlated with the melatonin concentration (p=-0.65, p<0.05). Based on that, an objective evaluation model for cognitive performance was proposed using the mean HR (R2=0.70, p<0.05) and melatonin concentration (R2=0.42, p<0.05). The quantitative relationships between the cognitive performance and two biomarkers (melatonin, HR) provided references for the working performance of people during the nighttime overtime.