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 de L'AQUILA - MEDICINA INTERNA E SANITA' PUBBLICA - ()

Research Unit Leader

Michele Ferrara

Description

In the present study we will investigate, on the field and in the laboratory, the effects of sleep loss, of 3 different napping strategies and of time-of-day on the executive control processes as assessed by a task switching procedure, a paradigm never used in the SD literature. Everyday life requires frequent shifts between different cognitive tasks. The ability to rapidly and flexibly adjust behavior to changing environmental demands is a defining characteristic of cognitive control and represents one of the most sophisticated capabilities of humans. This skill is clearly demonstrated within the context of experimental paradigms that require individuals to perform two or more different tasks in an intermixed fashion (here referred to as task switching). The task switching paradigm has been widely used to investigate the executive control of cognition (10, 19), and neuroimaging studies demonstrated that task switching performance recruits various PFC regions (1, 3, 25). In the task switching procedure, two different tasks are performed in rapid succession and according to a random sequence of task presentation, so that the to-be-executed task can change from one trial to the next (switch trial), or can be repeated (repeat trial). Task switches are usually behaviourally slower and less accurate than task repetitions. This difference is referred to as the task switch cost. The task switch cost as revealed by reaction time (RT) slowing is thought to reflect the time necessary to the executive control processes to reconfigure the cognitive system for the execution of a new task: thus it is an operational measure of the executive control.
Several aspects of cognitive control are involved in task switching, as suggested by the fact that the task-switch cost comprises different components (17). Specifically, task switching involves both perspective processes of task set reconfiguration (necessary for the execution of the new task) and processes related to the disengagement of the previously executed task. Accordingly, the switch cost (SC) is reduced when a cue is presented that indicates which task participants have to carry out on a specific trial, allowing to prepare before the imperative stimulus is presented; similarly, the cost is also reduced when the interval between the cue and the target presentation (CTI) increases, that is when more time is available for task set reconfiguration (18, 23). The SC is also reduced when the interval between the response on the previous trial and the presentation of the target stimulus for the new task is increased (RTI), suggesting that a task disengagement process is also involved in task switching (18). Finally, the SC is never completely abolished, even when very long time for task preparation is allowed, suggesting that a task set reconfiguration can be completed only after some perceptual task-relevant information is specified (17, 23).
Aims of the study
Junior doctors often experience an acute but complete loss of sleep. During the night shifts, interns are also required to have highly skilled performances. In these cases, the ability to focus attention, to learn, to decide, to effectively communicate and execute medical-surgical actions is absolutely needed. In the medical decision making, the so-called task switching, i.e. the quick and flexible adaptation of behavior to the changing characteristics and requests of the environment, is crucial. Such ability may be negatively impacted by sleep loss and fatigue. Consequently, during the night work an effective shift between anamnesis, diagnosis, prognosis and prescriptions may not be guaranteed.
Given the strict relations between sleep and frontal lobe functions, the first aim of the present study is to investigate on the field whether sleep loss during night shifts selectively affects specific components of the control processes involved in task switching. Moreover, we will test the hypothesis that one or two short naps (during or after the night shift) may improve the ability of task switching performance in junior doctors. This study will be preceded by 2 pilot experiments, with the aim of empirically choosing the task switching paradigm most sensitive to the effects of one night of total sleep deprivation. Finally, in a further experiment we will test the hypothesis that time-of-day affects the executive functions involved in task switching performance. In fact, to our best knowledge the time-course of task switching performance across the day has been never studied.

GENERAL METHOD
Participants
A total of 200 junior doctors (100 females) will be selected from the interns population of the Faculty of Medicine to take part in the “on the field” study. Half of the subjects will be expert interns (4th year of study), while the other half will be selected during the 2nd year of study. 60 other subjects will be selected from the same population to participating to the 2 pilot studies and to the “time of day” study. All subjects will sign an informed consent.
Apparatus and stimuli
Experiments will take place in a dimly lit room. Participants will seat in front of a 15-inch computer monitor, at a distance of 50 cm. Stimuli will consist of digits, from 1 to 9 (excluding 5), subtending approximately 3° x 5° of visual angle. Task cues stimuli will consist of outlined squares and diamonds, indicating the parity and magnitude tasks, respectively; they will subtend approximately 7° x 7° of visual angle. Cues and digits will be presented at the screen centre in white on black background; targets will be presented inside the cue frames. The same two response keys on the computer keyboard (“A” for left and “L” for right) will be used for both tasks. Stimuli presentation and response registration will be controlled by a custom program (Superlab 2.1 for Windows).
Task and assessment of the switch costs
Task switch costs will be assessed by means of a task-cueing procedure, which involves performing two tasks in rapid sequence according to a randomized order, and presenting a cue on each trial that indicates the task to perform on the subsequent target stimulus.
In each experiment the same two tasks will be used; they will consist of judging the parity of a digit stimulus (odd/even) or the magnitude of the digit stimulus (larger-/smaller-than-5). Participants will use their left and right index fingers for responding. Odd digits and Smaller-than-5 digits will be mapped onto the left-index finger response. Even digits and Larger-than-5 digits will be mapped onto the right-index finger response.
Participants will be tested individually. Task instructions will be both displayed on the screen and verbally explained to participants, emphasizing the need for both accuracy and speed. Switch costs will be measured as the difference in reaction times (RTs, speed measure) and proportion of errors (accuracy measure) between task switch trials and task repetition trials.
Subjective Measures
Before each task switching session, self-rated sleepiness will be measured by the Karolinska Sleepiness Scale (KSS) and subjective mood by a Visual Analog Scale.

PILOT EXPERIMENTS
The aims of this experiment are: a) to evaluate which task switching component (the endogenous component of task set reconfiguration or the decay component) is the most negatively affected by sleep deprivation, so that the most sensitive configuration of the task will be used in the following “on the field” study; b) to study the effects of sleep loss on task switching performance in a typical laboratory controlled inactive condition, in order to compare the simple effects of sleep loss per se with the cumulative effects of sleep debt and operational fatigue due to working the night shift.
Pilot 1
In order to investigate the effect of sleep deprivation on the endogenous components of task set reconfiguration independently from the decay component of task set, the RTI will be held constant at 1300 ms while the CTI will be manipulated by presenting the cue either far from the previous response and close to the incoming stimulus (i.e., Response-Cue Interval or RCI = 1000 ms and CTI = 300 ms) or close to the previous response and far from the incoming stimulus (i.e., Response-Cue Interval = 300 ms and CTI = 1000 ms). Therefore, we will have two conditions of RCI-CTI: long-short and short-long. On each trial, a cue will be presented for 300 or 1000 ms (depending on the experimental condition) and will be followed by a target stimulus. Both the cue and target stimuli will remain on the screen until participant’s response or 2500 ms will be elapsed.
20 junior doctors will be randomly assigned to one of two different groups (Experimental and Control groups; 10 ss for each group). Each group will undergo 4 task switching sessions, with the Training session performed on day 1, the Baseline session on day 2, the Experimental session on day 3 after the night shift (Experimental group) or normal sleep at home (Control group), and the Recovery session on day 4 after a night of recovery sleep. Each session will start at 11 a.m. All the Training, Baseline, Test and Recovery sessions will consists of 2 separate subsessions each, differing each other in the RCI and CTI combination. In the present experiment the RCI-CTI combination will be long-short in one sub-session and short-long in the other sub-session. The order of sub-sessions presentation will be balanced between subjects.
Pilot 2
In order to investigate the effect of sleep deprivation on the decay component of task switching independently from the task set reconfiguration processes, the CTI will be kept constant at 300 ms, while the RCI will be manipulated by presenting the cue either far from the previous response and close to the incoming stimulus (i.e., RCI = 1000 ms and CTI = 300 ms) or close to the previous response and close to the incoming stimulus (i.e., RCI = 300 ms and CTI = 300 ms). Therefore, in the Pilot experiment 2 we will have two conditions of RCI-CTI: long-short (1000-300; which is the same as on the Pilot experiment 1) and short-short (300-300). As before, the 20 interns will be randomly assigned to one of the 2 conditions (10 to the Experimental group, 10 to the Control group). Similarly, task switching sessions will consists of 2 separate sub-sessions each, and the sub-sessions will differ for the RCI-CTI combination (long-short in one sub-session and short-short in the other). In these conditions, the interval between the cue and the current stimulus is always 300 ms, while the RTI is 1300 in the long-short condition (1000+300 ms) and 600 ms in the short-short condition (300+300 ms).

“ON THE FIELD” EXPERIMENT
Each of the 10 experimental groups will comprise 20 junior doctors routinely involved in night shifts (matched for age, gender and expertise level). The complete experimental protocol is reported in the following scheme. All subjects will wear an actigraph on the nondominant wrist from Day 1 to Day 3 (nights included). Actigraphic recordings will allow to estimate the nocturnal sleep and nap duration (where scheduled), and to identify the presence of unintended unscheduled naps.

Briefly, all groups will be trained to asymptote at 11 a.m. on Day 0 and tested for the Baseline performance at the same time on Day 1.
During the following night (Night 1), the 2 “Control” groups (A and B) will regularly sleep at home, monitored by actigraphy. Then, both groups will be retested at 11 a.m. on Day 2, while only the B subgroup will be also retested at 4 p.m. A final retest will be carried out at 11 a.m. on Day 8.
The 2 “Wake” groups (A and B) will work all night long during their night shift (Night 1). They will be tested on Day 2 at 11 a.m., to assess the effects of sleep loss and fatigue on the task switching performance. The subgroup B will be also retested on Day 2 at 4 p.m. Both the subgroups will be tested again on Day 3 at 11 a.m., after one night of recovery sleep (Night 2) at home, monitored by actigraphy. A final retest will be carried out at 11 a.m. on Day 8.
The 2 “Nocturnal Nap” groups (A and B) will be allowed a brief period of sleep (up to 45 min) during their night shift (Night 1). Then, both groups will be tested on Day 2 at 11 a.m., to assess the recuperative effects of the nap on the task switching performance. The subgroup B will be also retested on Day 2 at 4 p.m. Both groups will be tested again on Day 3 at 11 a.m., after one night of recovery sleep (Night 2) at home, monitored by actigraphy. A final retest will be carried out at 11 a.m. on Day 8.
Also the 2 “Nocturnal and P.M. Nap” groups (A and B) will be allowed a brief nap (up to 45 min) during their night shift (Night 1). However, after the test on Day 2 at 11 a.m., both groups will be allowed another nap opportunity at 2 p.m. The subgroup B will be also retested on Day 2 at 4 p.m., to assess the cumulative effects of the 2 naps on the task switching performance. Both groups will be tested again on Day 3 at 11 a.m., after one night of recovery sleep (Night 2) at home, monitored by actigraphy. A final retest will be carried out at 11 a.m. on Day 8.
The 2 “P.M. Nap” groups (A and B) will work all night long during their night shift (Night 1). They will be tested on Day 2 at 11 a.m., then they will be allowed a nap opportunity at 2 p.m., followed by a further retest at 4 p.m. only in the B subgroup. As before, both groups will be tested again on Day 3 at 11 a.m., after one night of recovery sleep (Night 2) at home, monitored by actigraphy. A final retest will be carried out at 11 a.m. on Day 8.

“TIME OF DAY” EXPERIMENT
To assess the effects of time-of-day on the executive functions involved in task switching performance, 20 junior doctors will be administered task-switching sessions at regular intervals during the daytime (every two hours, from 10.00 a.m. to 10.00 p.m.). Therefore each participant will undergo 7 task switching sessions. As in the previous experiments, each session will last 40 minutes. For half the participants (n=10), sessions will be RCI-CTI combination: long-short and short-long; for the other 10 subjects, sessions will be RCI-CTI combination: long-short and short-short. During the intervals between sessions participants will be free to rest or carry out their normal daytime activities, but they will be not allowed to nap, as monitored by actigraphy.