title: Dynamics of neurobehavioral performance variability under forced desynchrony: evidence of state instability.
abstract: OBJECTIVE
  The state instability hypothesis posits that increasing sleep drive brings about escalating state instability in attention, making neurobehavioral performance increasingly variable. This hypothesis predicts that performance variability is a function of prior wake, circadian phase, and time on task. These predictions have been supported when wakefulness is beyond the habitual wake period. Our study aimed to test these predictions within the habitual wake period.
  
  
  METHODS
  A 12-calendar-day 28-h forced desynchrony protocol consisting of 7 repetitions of a 28-h sleep/wake cycle, with two-thirds time awake and one-third time in bed. Each wake period included 7 equally spaced 1-h testing sessions.
  
  
  METHODS
  A time-isolation sleep laboratory.
  
  
  METHODS
  Thirteen young healthy males.
  
  
  METHODS
  Wake periods during the protocol were 4 h delayed each 28-h "day" relative to the circadian system, such that they were distributed across the whole circadian cycle. This allowed performance testing at different combinations of prior wake of a habitual length (i.e., < 18 h) and circadian phase.
  
  
  RESULTS
  Performance variability was indexed by standard deviation of response times within a 10-min psychomotor vigilance task. We found that response times became more variable with increasing wakefulness and towards circadian nadir, i.e., when sleep drive was increasing. These changes in response time variability were however not dependent on time on task, which is likely due to the modest level of sleep drive in our study.
  
  
  CONCLUSIONS
  The state instability hypothesis, as an explanation for the responsiveness of neurobehavioral performance to increasing sleep drive, is supported during the habitual wake period.
authors.affiliation: Centre for Sleep Research, University of South Australia, Adelaide, Australia. xuan.zhou@unisa.edu.au
authors.forename: Xuan
authors.initials: X
authors.lastname: Zhou
authors.forename: Sally A
authors.initials: SA
authors.lastname: Ferguson
authors.forename: Raymond W
authors.initials: RW
authors.lastname: Matthews
authors.forename: Charli
authors.initials: C
authors.lastname: Sargent
authors.forename: David
authors.initials: D
authors.lastname: Darwent
authors.forename: David J
authors.initials: DJ
authors.lastname: Kennaway
authors.forename: Gregory D
authors.initials: GD
authors.lastname: Roach
mesh_terms: D000293:Adolescent; D000328:Adult; D001288:Attention / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology*; D006801:Humans; D008297:Male; D017286:Polysomnography; D011597:Psychomotor Performance / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D012890:Sleep / Q000502:physiology; D014851:Wakefulness / Q000502:physiology; D055815:Young Adult