The goal is to investigate if the morningness-eveningness dimension mediates sleep and function on spilt night shifts (midnight-4am and 4am-8am). Does those with high score of morningness function relatively better on the last compared to the first split shift? Participants will: Record their sleep from 2 days prior to 2 days following the split shift During the shifts complete questionnaires assessing mood, sleepiness and perceived performance as well as complete cognitive tests: Psychomotor vigilance test, digit symbol substitution test, working memory scanning test, reversal learning test, and visual search test
A sample of 28 students will be recruited and exposed to two conditions in a randomized, controlled, crossover study. They will be assessed with subjective (sleep diary) and objective sleep measures (sleep radar) for 2 days before the night shift, during the night shift and 2 days following the night shift. The simulated night shifts will last from midnight to 8am and will be divided into two halves (midnight-4am and 4am-8am), denoted as split-shift, and for each participant separated by at least 1 week. Based on the Horne-Östberg Morningness-Eveningness Questionnaire (median spilt) two groups are created, from which participants will be randomized to the two orders of the spilt-shift. Each hour on each shift the participants will complete: Positive and Negative Affect Schedule (PANAS), Karolinska Sleepiness Scale, perceived performance and the following cognitive tests: Psychomotor vigilance test, Digit symbol substitution test, Working memory scanning test, Reversal learning test, and Visual search test. Data will be analyzed with linear mixed models with three fixed factors: Group (low vs. high morningness), shift (midnight-4am vs. 4am-8am), and hour and one random factor (participant).
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
NONE
Enrollment
30
Early vs. late night split night shift
University of Bergen
Bergen, Norway
Total sleep time
Total sleep (sleep diary and radar). Higher values indicates more sleep
Time frame: Total sleep time between 6pm day before shift start to 6pm the day the shift end for both early night shift (midnight-04am) and late night shift (04am-08am)
Psychomotor Vigilance Test (PVT)
Reaction time (mean 1/RT) and number of lapses (RTs≥500 ms). For mean 1/RT higher values are associated with best performance, on lapses higher values are associated with worst performance
Time frame: Hourly during shifts (0:15am, 1:15am, 2:15am and 3:15am on early night shift; 4:15am, 5:15am, 6:15am and 7:15 am on late night shift)
Karolinska Sleepiness Scale (KSS)
Assessment of state sleepiness, range 1-9 (higher scores indicate worse state)
Time frame: Hourly during shifts (0:15am, 1:15am, 2:15am and 3:15am on early night shift; 4:15am, 5:15am, 6:15am and 7:15 am on late night shift)
Sleep efficiency (percentage of time in bed one sleeps)
Sleep efficiency (diary and radar). Range from 0-100%. Higher scores indicate best state
Time frame: Between 6pm day before shift start to 6pm the day the shift end for both early night shift (midnight-04am) and late night shift (04am-08am)
Positive and Negative Affect Schedule (PANAS)
Assessment of mood/affect. Range 10-50. On positive mood subscale higher scores indicate best state, on negative mood state, higher scores indicate worst state
Time frame: Hourly during shifts (0:15am, 1:15am, 2:15am and 3:15am on early night shift; 4:15am, 5:15am, 6:15am and 7:15 am on late night shift)
Self-rated performance
Self-rated performance on cognitive tests. Range 1-10. Higher scores indicate best performance rating
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Time frame: Hourly during shifts (0:15am, 1:15am, 2:15am and 3:15am on early night shift; 4:15am, 5:15am, 6:15am and 7:15 am on late night shift)
Digital Symbol Substitution Test
Test where one match symbols to numbers as fast as possible. Range 0-100. Higher scores indicate best performance
Time frame: Hourly during shifts (0:15am, 1:15am, 2:15am and 3:15am on early night shift; 4:15am, 5:15am, 6:15am and 7:15 am on late night shift)
Working Memory Scanning Test (probed recall)
Test presenting list of words. Then words are presented and subjects decide if word was present or not in list presented. The accuracy and RTs for positive trials (where probe was present in list) will be used as dependent variables. Higher accuracy and lower reaction time are associated with best performance
Time frame: Hourly during shifts (0:15am, 1:15am, 2:15am and 3:15am on early night shift; 4:15am, 5:15am, 6:15am and 7:15 am on late night shift)
Reversal Learning Test
Test measuring the ability to differentiating between "go-stimuli" and "no-go stimuli" before and after reversal of go and no-go stimuli. Discriminability (hit rate/false alarm rate) and response bias before and after reversal are recorded. Higher discriminability indicates better performance, higher response bias indicate worse performance
Time frame: Hourly during shifts (0:15am, 1:15am, 2:15am and 3:15am on early night shift; 4:15am, 5:15am, 6:15am and 7:15 am on late night shift)
Visual Search Test
Multiple objects are presented, and from among them a target is identified. The task of the subject is finding the target. Outcomes are reaction time (RT) and accuracy. Lower reaction times and higher accuracy are associated with best performance
Time frame: Hourly during shifts (0:15am, 1:15am, 2:15am and 3:15am on early night shift; 4:15am, 5:15am, 6:15am and 7:15 am on late night shift)