Shift work sleep disorder is associated with an attenuated brain response of sensory memory and an increased brain response to novelty: an ERP study.

Study Objective: To study the neurophysiological changes in attention and memory functions in shift work sleep disorder (SWSD), using event-related brain potentials (ERPs).

Participants: 9 healthy night workers (NW) (mean age = 40 y; SD +/- 8.9 y); 8 night workers meeting diagnostic criteria for SWSD (mean age = 37 y +/- 9.4 y) and 9 healthy day workers (DW) (mean age = 35 y +/- 7.3 y).

Methods And Procedure: Using standard PSG the sleep related measures (TIB, TST, SOL, SE, and sleep stage distribution) were obtained prior to EEG/ERP study. Measures of habitual sleep were obtained from 2 week sleep logs and sleepiness was assessed with standardized measures. Using 32-EEG leads the ERPs to 3 types of sounds (novel, duration deviant, and simple tone) were obtained. The mismatch negativity (MMN) reflecting memory processing and P3a-reflecting the shift of involuntary attention were obtained.

Statistical Analysis: The statistical comparisons of ERPs and sleep related parameters were performed using repeated measured ANOVAs and t-tests where appropriate.

Results: Patients with SWSD had reduced TST and increased WASO relative to healthy workers. ERP results demonstrated significant attenuation of MMN amplitude over frontal regions in SWSD patients relative to NW and DW. In the SWSD patients, the P3a was increased to novelty across frontocentral brain regions with respect to the same locations in healthy controls.

Conclusion: The ERP evidence of sensory memory reduction and attentional hyper-reaction to novel sound in conjunction with disturbed sleep suggests the need for more neurophysiological studies in SWSD workers.