RICERCA ITALIANA     

Research program

Sleep-debt effects on procedural learning and on clinical and cognitive performance in resident physicians: the protective function of naps

University Co-ordinator

Università degli Studi di BOLOGNA - PSICOLOGIA - ()

Research Unit Leader

Carlo Cipolli

Description

AIMS - The two main aims of the project are to examine, by combining the procedures of field and laboratory studies within a crossover experimental design,
a) how acute sleep loss influences subsequent cognitive performance and learning of new perceptual and motor skills
b) how napping strategies can prevent or reduce this negative influence. The possible additive effect of concomitant chronic partial sleep deprivation (likely to occur above all in the residents in their 4th year of training) will also be evaluated.
PARTICIPANTS
The project consists of two complementary experiments to be carried out on two homogeneous groups respectively of 240 and 200 junior doctors (half males and half females of 2nd- and 4th-year of the postgraduate program).
Each sample will be selected from the intern population of the post-graduate program of the Faculty of Medicine of the University of Bologna (those available to take part in a 64-hour “field” study). Eligible subjects will be right-handed, 26 to 32 years old, without sleep disorders (QDS), with an intermediate circadian typology (MEQ), without cognitive, motor or perceptual disorders (as preliminarily assessed) and not pharmacologically treated for any medically relevant disease (GHQ-12). Participants in the study will have accepted a) to maintain a regular wake/sleep rhythm in the week preceding and following the experiment and b) to compile a sleep diary.
Participants will be informed as to the general aims of the study and will sign an informed consent before entering the experimental routine.
PROCEDURE
Experimental design - According to the experimental design (the same adopted in all other units) each of the two samples (sample 1 consisting of 240 doctors; sample 2 consisting of 200 doctors) of young doctors will be subdivided in 10 experimental subgroups. Those of sample1 included 24 participants (matched for age, gender and expertise level) and those of sample2 20, routinely involved in on-call duty and night shifts. The complete protocol can be described as follow.
The 2 “Control” subgroups (A and B) will sleep at home as normal during both Night 1 and 2, and will be monitored by actigraph, while the other 8 subgroups (nightwork subgroups) will be involved in on-call or night shift duties under the control of senior doctors, who will have an explicit function of tutor for the activities of the young doctors. Two of the 8 “experimental” subgroups (C and D) will remain awake during the night and following day, that is, without the possibility of taking any night- or day-time nap; two other subgroups (E and F) will take a nap not longer than 45 minutes (as a posteriori estimated by examining actigraphic recording) at the moment chosen by each participant according to subjectively estimated sleepiness and the concomitant needs of medical work from 2 to 5 a.m.; two other subgroups (G and H) will take a night-time nap like the participants of E and F subgroups, and a second daytime nap not longer than 45 minutes (as a posteriori estimated by examining actigraphic recording) at about 2 p.m; two other subgroups (I and L) will remain awake over the night and will take a daytime nap not longer than 45 minutes at about 2 p.m.
All participants will wear an actigraph on the nondominant wrist continuously, from the night preceding Day 1 until Day 3 (including the two intermediate nights) in order to estimate the duration of nocturnal sleep (when permitted) and of naps (when scheduled), as well as to identify retrospectively the presence of unintended naps or microsleep episodes. Participants with unintended naps or more than 2 microsleep episodes (shorter than 5 min) will be excluded from statistical analyses and substituted by other residents.
Apparatus and stimuli
Experimental tasks will be carried out in quiet rooms of divisions of the university hospital “S. Orsola-Malpighi” in Bologna, where participants in the study are involved in clinical and didactic activities. Stimuli for each task will be generated and participants’ responses will be recorded by means of a laptop, the software of which will be checked weekly by expert technicians, to maintain the reliability of the assessment.
Objective measures for Sample 1.
Sample 1 will be engaged in two tasks, one to be carried out on days 1, 3 and 8, and the other on days 2, 3 and 8. The two task schedules intend to ascertain, respectively, a) the effect of post-training sleep deprivation (tempered or not by one or two naps), due to a working night, on the further consolidation of task-specific procedural skills; b) the effect of sleep deprivation (tempered or not by one or two naps) on the acquisition and consolidation of task-specific procedural skills. The nap to be taken at night and/ or in the afternoon will be no longer than 45 minutes. In this way, it will be assessed whether one of two naps has a preventive/ restorative effect against the deterioration of the previously learnt skills and/or the impaired acquisition of new skills.
Each subgroup will be assigned to either task condition, namely Texture Discrimination Task (TDT) or Finger Tapping Task (FTT), to be performed once on Day 1; the other task will be carried out once or twice (see below) on Day 2. Therefore, 5 subgroups (A, C, E, G, I) will be tested on TDT on days 1, 3 and 8, and on FTT on days 2 (once or twice according to the experimental design), 3 and 8, always from 11 to 12 a.m. (except for re-test of FTT at 4 p.m. for half of the participants of each subgroup, randomly selected).
The other 5 subgroups (B, D, F, H, L) will be tested on FTT on days 1, 3 and 8, and on TDT on days 2 (once or twice: see below), 3 and 8, always from 11 to 12 a.m. (except for re-test of TDT at 4 p.m. for half of the participants of each subgroup, again, randomly selected). The complete picture of the measures obtained should allow us to distinguish the possible preventive/ restorative effect of afternoon naps from the effect of one night of recovery sleep (night 2 being spent at home by all participants), with respect to new perceptual (TDT) and motor (FTT) procedural skills.
Texture Discrimination Task (Karni and Sagi, 1991). Subjects evaluate complex visual stimuli (presented via a laptop) by identifying both a central fixation letter (T or L) and the orientation of three diagonal bars. A session is composed of three sequential displays for each of the 50 trails of each block. A) A cross is displayed at the centre of the screen to indicate the fixation point. B) The target display is shown for 16 ms. C) A masking pattern (made of randomly oriented v-shaped micropatterns, with a “T” or “L” shaped figure in the centre) is presented for 100 ms. The interval between target display and masking pattern (stimulus onset asynchrony, OSA) at an accuracy rate of 80% of responses indicates the discrimination difficulty and measures the learning level. Thus, an increase in perceptual ability corresponds to a reduction in SOA threshold between the first (training) and the second or further (retrieval) sessions.
Finger Tapping Task (Walker et al., 2002, 2003). This task involves learning to tap as quickly and accurately as possible with the 4 fingers of the non-dominant hand a five-item ordered sequence of keys on a laptop keyboard without visual feedback. The numeric sequence (4-1-3-2-4) is displayed at the top of the screen to exclude any working memory component from the task. The computer records key press responses: each 30-sec trial is scored for the number of complete sequences achieved (speed) and the number of errors over sequences (error rate). The training session consists of 12 30-sec trials with 30-sec rest periods between trials (a total of about 12 min). The scores (speed and error rate) from the first trial of the training session are taken as a baseline measure, while averaged scores from the final three trials are taken as measures of the learning level reached.
Subjective Measures for sample 1
During the daytime, at about 10 a.m., participants will fill in the abbreviated form of the Profile of Mood States (POMS-B; McNair, Lorr, & Droppleman, 1992) and the Trait subscale of the State-Trait Anxiety Inventory (STAI-Y; Spielberger, 1989).
POMS-B is a shortened version of 65-item POMS, a tool widely used in both clinical and experimental settings for assessing fluctuations of mood states (see also O’Connor, 2004). It consists of 30 adjectives, rated on a 5-point scale, designed to assess six mood states: tension, depression, confusion, anger, vigour, fatigue. For this study, participants will be asked to respond on the basis of their immediate feelings.
The trait scale of STAI-Y consists of 4-point 20 items, assessing relatively stable individual differences in anxiety proneness.
In addition, after each task session (i.e., 3 or 4 times, according to subgroup), the short version of POMS for Vigor and Fatigue 5-adjective subscales will be administered to assess variations in anxiety and feelings of having/not having the capacity to complete mental or physical activities.
Finally, before each task session, self-rated sleepiness will be measured by the 7-point Stanford Sleepiness Scale (SSS), ranging from complete alertness to sleep onset.
Objective measures for Sample 2.
Sample 2 will be engaged in two tasks, to be carried out in the same order, in each task session of days 1, 2, 3 and 8. The two tasks will be administered in order to ascertain to what extent logical reasoning abilities and psychomotor vigilance (both of which are skills necessary for any real medical activity) are impaired after sleep deprivation (tempered or not by one or two naps, respectively at night and/or in the afternoon) due to a working night. In this way, we expect to collect adequate data to establish whether one of two naps have a restorative effect against the deterioration of previously learnt skills and/or of new learnt skills.
Sample 2 will be subdivided into 10 subgroups of 20 participants, according to the same design applied on sample 1.
All 10 subgroups of participants will be administered the Psychomotor vigilance task followed by the Logical Reasoning Task (on Day 1 for training, on the following days for testing, always at about 11 a.m.).
Psychomotor vigilance task (PVT: Dinges & Powell, 1985 ). PVT is the most frequently-used measure for the evaluation of objective vigilance as proved to be sensitive to sleep loss (Van Dongen et al, 2003). PVT is a simple visual reaction task lasting 10 minutes. Its basic measures are the following: a) mean reaction time (mean RTs), b) number of lapses (RT>500 msec), c) mean value of 10% fastest responses, d) mean values of 10% slowest responses. Measures b) and d) are considered to be highly sensitive to sleep pressure (Drummond et al., 2005). PVT measures the variations in vugilance during periods of sleep deprivation compared with those of baseline (day 1) and of partial recovery (day3) and complete recovery from sleep loss (day 8), as well as possible intermediate phases during the day after night-work (i.e. after a night-time or daytime nap, or both).
The Logical Reasoning Task (LRT: Baddeley, 1972) measures verbal reasoning ability and is a 64-trial timed task (3-min or multiples). In each trial two possible pairings ("AB" or "BA") are presented with either an accurate descriptor (logically valid premise) or an inaccurate descriptor (logically invalid premise). The participant has to decide if the premise is true or false. Four blocks of 64 trials (the order of which will be balanced across tests and participants) will be administered at each testing session (requiring 12 min). The number of exact responses per time unit (3 min) and proportion of exact responses over all responses will be computed.
Subjective Measures for sample 2
Participants of sample 2 will fill in the same subjective measures form as sample 1 according to the same administration procedure.
DATA ANALYSIS
Actigraphic data (collected from each participant for 8 days, ie. from the eve of day 1 until day 8) will be scored using software routines for the detection and classification of sleep-wake changes in terms of rest-activity cycles. The automatic analysis of motor activity indicators will allow us to assess the rest-activity cycles, their duration and the temporal location of intended (naps) and unintended (microsleep) sleep episodes over the period of sleep deprivation and during the following day, as well as in the days following the working night.
Sleep time and nap duration will be taken as dependent variables for between-group comparison of sleep organization and as covariates in statistical analyses of cognitive performance and learning.
Data regarding procedural skills (sample 1) will take “sleep loss” (five levels) and “learning phase” (three levels, namely training vs. retrieval 1 and retrieval2) as independent variables, and the TDT SOA value and the number of correctly reproduced sequences at FTT as dependent variables.
Data regarding psychomotor vigilance level and logical reasoning task (sample 2) will take “sleep loss” (five levels) and “vigilance condition”(four levels, namely baseline, sleep loss, partial recovery and final recovery) as independent variables, and two blocks of dependent variables drawn from PVT and LRT scores (see above) as dependent variables.
Considering subjective measures, scores of six POMS-B subscales will be used as dependent variables in separate mixed ANOVA designs, with sleep loss and learning phase as independent variables for assessing mood variations in relation to different sleep deprivation and napping strategies. STAI-Y trait Anxiety scores will be used as covariates in the above analyses to control the possible confounding effect of individual differences in anxiety proneness on scores of perceptual and motor tasks.

EXPECTED RESULTS
On the basis of the hypothesis of sleep having an important role both in maintaining effectiveness in the performance of psychomotor vigilance and reasoning abilities, and in consolidating previously acquired (learning phase) and newly acquired procedural skills (acquisition phase), four main results are expected. Sleep deprivation due to night-work should impair:
1) psychomotor vigilance and reasoning ability compared with the control condition (i.e., the performance of the control group). The impairment should be higher for sleep-deprived no-nap subgroups, compared with the two subgroups taking one nap and, above all, compared to the two subgroups taking two naps. The impairment should be transitory, performance scores being expected to reach baseline value, after one recovery night and especially after 7 recovery nights;
2) the consolidation of procedural skills previously acquired compared with the control condition. The size of the impairment should be lower in patients taking a night-time nap than those taking an afternoon nap and lowest of all in those taking both these naps. The impairment should be permanent, the scores of TDT and FTT performance being expected to remain lower than those of participants in the control condition (i.e., without sleep deprivation) after one as well as after 7 recovery nights;
3) the consolidation of procedural skills acquired after sleep loss compared with the control condition. The size of the impairment should be lower for patients taking a night-time nap than those taking an afternoon nap and lowest of all in those taking both these naps. The impairment should be permanent, the scores of TDT and FTT performance being expected to remain lower than those of participants in the control condition (i.e., without sleep deprivation) after one as well as after 7 recovery nights;
4) the learning process (and perhaps performance requiring vigilance reasoning ability) more severely in the participants (above all of the 4th year) with chronic partial deprivation of sleep (as assessed by sleep diary) than those without.