Sleep loss, circadian mismatch, and abnormalities in reorienting of attention in night workers with shift work disorder

Abstract

Study objectives: Permanent night-shift workers may develop shift-work disorder (SWD). In the current study, we evaluated neurophysiological and behavioral indices of distractibility across times prior to the night shift (T1), during night hours (T2), and after acute sleep deprivation (T3) in permanent hospital night workers with and without SWD.

Methods: Ten asymptomatic night workers (NW) and 18 NW with SWD participated in a 25-h sleep deprivation study. Circadian phase was evaluated by dim-light salivary melatonin onset (DLMO). Objective sleepiness was evaluated using the Multiple Sleep Latency Test (MSLT). Electrophysiological distractibility was evaluated by brain event-related potentials (ERP), whereas behavioral distractibility was evaluated by performance on a visual task in an auditory-visual distraction paradigm.

Statistical analyses: Comparisons of ERP results were performed by repeated-measures analysis of variance, and t-tests were used where appropriate. A Mann-Whitney U test was used for comparison of variables (MLST, Stanford Sleepiness Scale, and DLMO) that deviated from normal.

Results: First, in the SWD group, the reorienting negativity ERP amplitude was significantly attenuated compared to that in the NW group. Second, the SWD group had shorter MSLT during night shift hours (4.8 ± 4.9 min) compared to that in NW (7.8 ± 3.7 min; U = 47; z = -2.1; P < 0.03). Third, NW with SWD had a DLMO at 20:27 ± 5.0 h, whereas healthy NW had a DLMO at 05:00 ± 3.4 h (U = 43.5; z = -2.22, P < 0.03). Finally, acute sleep deprivation impaired behavioral performance and the P3a ERP in both groups.

Conclusions: Our results demonstrate specific deficits in neurophysiological activity in the attentional domain among the shift-work disorder group relative to night workers.

Keywords: ERPs; Shift work disorder; circadian phase; distractibility.

Figure 1

An illustration of the laboratory study protocol. M, sample for melatonin assay; SSS, Stanford Sleepiness Scale; MSLT, Multiple Sleep Latency Test; ERP, event-related brain potential study.

Figure 2

An illustration of the auditory-visual distraction paradigm. Auditory: non-distracted sounds were frequently presented pure tones intermixed with 20%- novel/distracted (environmental) sounds. Visual task consisted of 50% of letters and 50% of numbers randomly occurred on the computer screen every 1.2 sec.

Figure 3

Group averaged LOWESS fit curves of salivary melatonin (means and SEM) for asymptomatic night workers (NW) and shift work disorder (SWD) groups. Time of day is a clock time when saliva ample was collected for each participant.

Figure 4

(A) Mean sleep latency in min for each single sleep test for each group. The means of five tests recorded between 22:30 and 06:30 was significantly different between groups (see Results). (B) Means of Stanford Sleepiness Scale scores for each group. The bars represent the errors for each measure. MSLT, Multiple Sleep Latency Test; NW, night workers; SSS, Stanford Sleepiness Scale; SWD, shift work disorder.

Figure 5

Behavioral data (means, SD and SEM) obtained in T1 session (18:00) shows similar distraction effect caused by distracted sounds with respect to non-distracted sounds in reaction time (RT), accuracy (correct rate) and errors in both groups. NW, night workers; SD, standard deviation; SEM, standard error of the mean; SWD, shift work disorder. *Indicates significance in P-values (see Results).

Figure 6

Event-related brain potentials elicited to nondistracted and distracted stimuli at Fcz electrode for both groups in T1, T2, and T3 sessions. The visual stimuli onset, depicted by the dashed line, was at 300 ms. NW, night workers; SWD, shift work disorder.

Figure 7

The difference waveforms at Fz and Cz electrodes obtained from both groups in T1, T2 and T3 sessions. The gray highlighted the latency range for significant differences between groups in RON component. NW, night workers; RON, reorienting negativity; SWD, shift work disorder.

Figure 8

Two-way interaction (group × time) shows significant attenuation of the RON amplitude in SWD group with respect to NW group in T1 and T2 sessions. In T3, the RON was similar between two groups across three frontal electrodes. NW, night workers; RON, reorienting negativity; SWD, shift work disorder. *P < 0.03, **P < 0.004.