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 TRIESTE - PSICOLOGIA - ()

Research Unit Leader

Corrado Cavallero

Description

Main goal of the Trieste unit is to evaluate the impact of sleep deprivation on attention and executive control of junior doctors during their postgraduate training. The unit will adopt an experimental design shared by the other units of the main project. Focus of the research will be the deterioration immediately following sleep loss as well as deferred or long-term one (after both one night of recuperative sleep and one week of regular sleep-wake schedule). It is possible indeed that 24 hrs of sleep deprivation have a negative impact on the acquisition and consolidation, by the participants, of those abilities needed to efficiently perform in the various task. That is, the natural ability of an individual to familiarize with a given task and develop strategies which enable her to better perform over time could be impaired by sleep loss. At the same time we want to determine the efficacy of a napping strategy against the negative effects of sleep loss taking into account not only the presence absence of one or two naps but also their positioning throughout the 24 hrs. Two additional factors will be considered: Gender and Exposure to sleep deprivation. Groups will be balanced by gender, in order to detect potential differences between females and males, and Exposure to sleep deprivation. This factor is intended to differentiate between junior doctors who are facing their first night shifts, and those who have already experienced a number of years of overnight work. It is possible indeed that junior doctors towards the end of their postgraduate training have been able to adopt some strategy or technique to reduce the negative effects of work-related sleep loss.
The interest for high level cognitive processing is motivated by the characteristics of the work environment under study. In the hospital, young residents, besides having to maintain a constantly efficient level of attention, are daily facing new clinical tasks they encounter for the first time. They have to deal with procedures and information not yet fully learned and consolidated which are, in addition, highly different from one another. It should be clear the importance in this work environment of cognitive abilities such as resistance to distraction, focusing of attention, inhibiting an ongoing response as soon as one realizes it is the wrong one. But in order to obtain results which go beyond a generic interpretation in terms of unspecified attention deficits (Kjellberg, 1977) one has to take into consideration theoretical models derived from cognitive science. As far as attention is concerned, the model developed by Posner and co-workers (Posner & Raichle, 1994; Posner & Petersen, 1990) appears to be pertinent and promising. In this model attention is divided into three functionally independent networks that carry out the functions of alerting, orienting and executive control. Alerting is defined as achieving and maintaining an alert state; Orienting is the selection of information from sensory input; and Executive control is defined as resolving conflict among responses. Many neuroimaging studies suggest different anatomies of the three networks (Corbetta & Shulman, 2002; Fan, et al., 2003; Posner & Petersen, 1990). The alerting system has been associated with the frontal and parietal regions of the right hemisphere, The orienting system has been associated with areas of the parietal and frontal lobes, and finally, executive control of attention is associated with midline frontal areas (anterior cingulate) and the lateral prefrontal cortex.
In order to obtain a measure of the efficiency of these three different functions of attention, Fan and co-workers (2002) have developed the Attention Network Test (ANT). This is a rapid (approximately 15 min.) and easy-to-use test which combines the Cued Reaction Time Task by Posner (1980) e the Flanker Task by Eriksen & Eriksen (1974). We chose this task because it allows to simultaneously verifying both performance levels (in terms of speed and accuracy) and the level of efficiency of the three attentional networks (Alerting, Orienting, and Executive Control). The necessity of measuring several aspects of the attentional system by means of a single instrument is dictated by the fact that attention is a multidimensional cognitive ability (Mirsky et al., 1991). Hence, it is not enough to establish a generic relationship between sleep loss and attention (almost exclusively in terms of vigilance deficit), but one has to specify whether, following sleep loss, there is a general impairment of attentional processes or only specific components are selectively damaged. Data on the efficiency of Executive Control network provide valuable cues about one of the main components of the executive functions: the ability of focusing attention on the relevant stimulus disregarding the surrounding irrelevant stimuli. This ability can be translated, from an ecological point of view, into the ability to resist distraction. Similarly, from an ecological point of view, the capacity of interrupt an ongoing action one which is wrong , in order to correct its consequences, corresponds, at an experimental level, to the ability to inhibit a dominant response. The Stop Signal Task is an instrument derived from the Stop Response Paradigm which has been developed by Logan & co-workers (Logan et al., 1997; Logan & Cowan, 1984). It is a rapid (about 10 min.) task which is able to give an accurate estimate of the efficiency of the process of inhibiting a dominant response. It s a very useful instrument in sleep deprivation research because inhibition is one of the main executive functions which are associated with metabolic activity in the lateral prefrontal cortex (Bush, Luu, & Posner, 2000) and have been shown particularly sensitive to sleep-wake cycle alterations (Harrison & Horne, 2000). Surprisingly enough, research on the effects of sleep deprivation on inhibition has led to contradictory results. There are data in favour of significant negative effects of sleep loss on inhibition processes (Drummond et al., 2006) and data that suggest that inhibition is untouched by sleep deprivation (Jennings et al., 2003). Being the stop signal test a task much more sensitive to subtle variations than the ones used until now in the literature (mainly go-no go tasks) it should be the best candidate to disambiguate the relationships between inhibition and sleep loss.
The project consists of two phases lasting 4, and 20 months respectively.
Phase I
In this phase, a group of 200 volunteers (100 females and 100 males), aged between 26 and 35 years will be selected. All of them must be junior doctors completing their post-graduate training at the medical school of the University of Trieste and University of Udine, enrolled in II and IV year of specialization courses. The aim is to obtain 4 groups of 50 participants each, characterized by the combination of the level of factors Gender (Female and Male) and Exposure to sleep deprivation (Low - junior doctors who are just starting working overnight - and High - junior doctors who are at their second/third year of overnight work). Hence, the four groups will be: female doctors of the II (F-II) and the IV (F-IV) years; male doctors of the II (M-II) and the IV (M-IV) years. All the potential participants to phase II will undergo an accurate screening by means of: (a) the QDS (Violani et al., 2000) in order to select only subjects with no major sleep disturbances; (b) a number of subscales about health conditions and psychological disorders derived from the Standard Shift-work Index (Burton, Spelten, Totterdel, Folkard, Costa, 1995) with the aim of excluding from the experimental sample subjects with medical complaints or borderline scores on anxiety, extraversion/introversion, and depression dimensions; (c) the MEQ (Horne & Ostberg, 1977) that will allow us to characterize study participants according to circadian typology (morning type and evening type) and exclude the most extreme typology.
Phase II
Each participant from the four groups (F-II, F-IV, M-II,M-IV) will be randomly assigned to one of five sleep deprivation conditions, C (Control – no deprivation), DT (total sleep deprivation), DNN (Deprivation + night nap), DNP (Deprivation + afternoon nap), DNNNP (Deprivation + night nap + afternoon nap). In this way, sleep deprivation conditions will have 40 participants each (10 F-II, 10 F-IV, 10 M-II e 10 M-IV). The forty participants of each deprivation condition will be randomly assigned to one of two test condition: TM (just one morning test session during the day following sleep deprivation/control); and TMP (1 morning plus 1 afternoon test session during the day following sleep deprivation/control). A group of 20 participants (5 F-II, 5 F-IV, 5 M-II e 5 M-IV) will be thus assigned to each combination of sleep deprivation and test conditions.
In Control condition (C), testing will be performed for the first time at 11/12 after an undisturbed night of sleep, TMP subgroup will be tested again few hours later (16/17), then all the participants will undergo a test session at 11/12 of the following day and a week after the first test session, always at 11/12.
In total sleep deprivation condition (TD), testing will be performed for the first time at 11/12 after a night on call, TMP subgroup will be tested again few hours later (16/17), then all the participants will undergo a test session at 11/12 of the following day and a week after the first test session, always at 11/12.
In deprivation + night nap condition (DNN), testing will be performed for the first time at 11/12 after a night on call during which participants will be allowed to take a short nap (20/45 min.) between 4 and 6 a.m., TMP subgroup will be tested again few hours later (16/17), then all the participants will undergo a test session at 11/12 of the following day and a week after the first test session, always at 11/12.
In deprivation + afternoon nap condition (DNP), testing will be performed for the first time at 11/12 after a night on call, then participants will be allowed to take a short nap (20/45 min.) between 2 and 3 p.m., TMP subgroup will be tested again few hours later (16/17), then all the participants will undergo a test session at 11/12 of the following day and a week after the first test session, always at 11/12.
In deprivation + night nap + afternoon nap condition (DNNNP), testing will be performed for the first time at 11/12 after a night on call during which participants will be allowed to take a short nap (20/45 min.) between 4 and 6 a.m., then they will be allowed to take a short nap (20/45 min.) between 2 and 3 p.m., TMP subgroup will be tested again few hours later (16/17), then all the participants will undergo a test session at 11/12 of the following day and a week after the first test session, always at 11/12.
All the participants will undergo actigraphic control from 6 p.m. of the day preceding the sleep deprivation/control night, till 11 a.m. of the day following the first recuperative night (about 41 hours). This control will enable us to check duration and quality of both sleep deprivation and recuperative sleep.
Test sessions will allow collection of subjective and behavioral data. At the beginning of each test session the subject will be given: (a) a visual-analog scale in order to assess subjective rating of vigilance and mood (Global Vigor Affect Scale – Monk, 1989); and (b) the Karolinska Sleepiness Scale (KSS – Akersted, 1990). Behavioral data will be collected by means of the ANT (Fan et Al., 2002) and the Stop Response test (Logan & Cowan, 1984) which will be given in counterbalanced order across sessions and experimental conditions. By means of these dependent variables we should be able investigate in high detail consequences of sleep reduction/deprivation on mood, attentional processing and executive control.
As far as attentional processing is concerned, we should be able to understand if sleep reduction/deprivation exerts either an unspecific effect on cognitive performance or a selective negative effect only on specific subcomponents of the attentional network.
By comparing data from the first test session we should be able to determine whether, and in what measure, (a) a sleepless night deteriorates performance in comparison with an undisturbed night and (b) a short night nap might counteract the negative effects of sleep loss.
By comparing the morning test session with the afternoon one for the various TPM groups it will be possible not only to verify whether the negative effect of sleep loss lasts, increases or even appears in the second half of the day following deprivation; but also to determine whether one or two short naps might restore, in the second half of the day, junior doctors’ performance to levels which are comparable to those of control condition.
We should be able to establish the recuperative power of a single night of undisturbed sleep (together with one or two short naps) by comparing the first test session with the one 24 hrs later.
Finally, we should be able to evaluate whether cognitive impairments connected with sleep loss are temporary or long-lasting by comparing the data obtained immediately after the sleep deprivation/control night with those collected a week later.
These results will be further enriched by the possibility to determine the role played by the factors Gender and Exposure to sleep deprivation, and their interaction. We should be able to
see whether: (a) women are better (or worse) than men to resist the negative effects of sleep curtailment; and (b) junior doctors in their IV year of postgraduate training have been able to adopt some strategy or technique to reduce the negative effects of work-related sleep loss.