Chronobiology International, 2014; 31(10): 1209–1217 ! Informa Healthcare USA, Inc. ISSN: 0742-0528 print / 1525-6073 online DOI: 10.3109/07420528.2014.957763 ORIGINAL ARTICLE The effects of a split sleep–wake schedule on neurobehavioural performance and predictions of performance under conditions of forced desynchrony* Anastasi Kosmadopoulos 1,2 , Charli Sargent 1 , David Darwent 1 , Xuan Zhou 1 , Drew Dawson 1 , and Gregory D. Roach 1 1 Appleton Institute for Behavioural Science, Central Queensland University, Adelaide, South Australia, Australia and 2 Bushfire Cooperative Research Centre, East Melbourne, Victoria, Australia Extended wakefulness, sleep loss, and circadian misalignment are factors associated with an increased accident risk in shiftwork. Splitting shifts into multiple shorter periods per day may mitigate these risks by alleviating prior wake. However, the effect of splitting the sleep–wake schedule on the homeostatic and circadian contributions to neurobehavioural performance and subjective assessments of one’s ability to perform are not known. Twenty-nine male participants lived in a time isolation laboratory for 13 d, assigned to one of two 28-h forced desynchrony (FD) schedules. Depending on the assigned schedule, participants were provided the same total time in bed (TIB) each FD cycle, either consolidated into a single period (9.33 h TIB) or split into two equal halves (2  4.67 h TIB). Neurobehavioural performance was regularly assessed with a psychomotor vigilance task (PVT) and subjectively- assessed ability was measured with a prediction of performance on a visual analogue scale. Polysomnography was used to assess sleep, and core body temperature was recorded to assess circadian phase. On average, participants obtained the same amount of sleep in both schedules, but those in the split schedule obtained more slow wave sleep (SWS) on FD days. Mixed-effects ANOVAs indicated no overall difference between the standard and split schedules in neurobehavioural performance or predictions of performance. Main effects of circadian phase and prior wake were present for both schedules, such that performance and subjective ratings of ability were best around the circadian acrophase, worst around the nadir, and declined with increasing prior wake. There was a schedule by circadian phase interaction for all neurobehavioural performance metrics such that performance was better in the split schedule than the standard schedule around the nadir. There was no such interaction for predictions of performance. Performance during the standard schedule was significantly better than the split schedule at 2 h of prior wake, but declined at a steeper rate such that the schedules converged by 4.5–7 h of prior wake. Overall, the results indicate that when the total opportunity for sleep per day is satisfactory, a split sleep–wake schedule is not detrimental to sleep or performance. Indeed, though not reflected in subjective assessments of performance capacity, splitting the schedule may be of some benefit, given its reduction of neurobehavioural impairment at night and its association with increased SWS. Therefore, for some industries that require operations to be sustained around the clock, implementing a split work–rest schedule may be of assistance. Keywords: Circadian rhythms, forced desynchrony, neurobehavioural performance, shiftwork, split shifts, sustained operations INTRODUCTION There is increasing expectation and demand for services that are available around the clock (Costa, 2003). As a consequence, more employees are undertaking shift- work outside traditional daytime work hours. However, despite the need for it, shiftwork is associated with suboptimum performance and an increased risk of fatigue-related injuries and accidents, particularly at night (Folkard et al., 2005; Folkard & Tucker, 2003; Muller et al., 2008). The increase in risk has largely been explained by circadian misalignment, difficulty in obtaining sufficient recuperative sleep, and long shift duration (Folkard et al., 2005; Folkard & Tucker, 2003; Philip & A ˚ kerstedt, 2006). Furthermore, there is evidence to suggest that assessments of one’s ability to perform during a week of simulated night shifts may only be *This article was presented at the 21st International Symposium on Shiftwork and Working Time, 4–8 Nov 2013, Bahia, Brazil. Correspondence: Anastasi Kosmadopoulos, Appleton Institute for Behavioural Science, Central Queensland University, PO Box 42, Goodwood, South Australia, Australia 5034. Tel: +618 8378 4527. Fax: +618 8378 4532. E-mail: a.kosmadopoulos@ cqu.edu.au Submitted February 10, 2014, Returned for revision August 4, 2014, Accepted August 20, 2014 1209