Introduction: Mind wandering, the drift of attention from the current task at hand to self-generated thought is commonly associated with poorer performance, and could be a potential pathway through which sleep deprivation affects performance. Little is known about this, however. Therefore, the aim of the present study was to address the effect of sleep deprivation on mind wandering and performance in a sustained attention task. In addition, we studied age as moderating factor, since older individuals are generally less prone to mind wandering.

Materials and methods: Healthy young (18-30years) and older (60-72years) subjects participated in either a normal night sleep (NSD) or a total sleep deprivation (SD) condition, i.e. 4 conditions: NSD (n=31), SD (n=30), NSDold (n = 24), SDold (n= 24). Performance was measured using the Sustained Attention to Response Task, during which 10 thought probes were included that prompted the subjects to answer a question on what they were you just thinking about, using predefined answer alternatives. Mind wandering was quantified as occurrence of task-unrelated thoughts.

Results: Applying a 2 (age) X 2 (sleep deprivation) ANOVA, significant main effects for sleep deprivation and age were observed for omissions, indicating worse performance after sleep deprivation and in young participants (p's < .05). These main effects were dominated by an age*sleep deprivation interaction (p = .04), which was due to sleep deprivation causing significantly more omission errors in young subjects (Mean ±SEM; NSD: 2.3 ±0.9; SD: 13.1 ±4.1) but not in older subjects (NSDold: 1.9 ±0.4; SDold: 2.8 ±0.9).

Likewise, main and interaction effects for age and sleep deprivation were significant for task-unrelated thoughts (p's < 0.01). Task unrelated thoughts were significantly more frequent after sleep loss in young (NSD: 1.5 ±0.2; SD: 4.3 ±0.6), but not older subjects (NSDold: 0.3 ±0.2; SDold: 0.5 ±0.2) (interaction age*sleep deprivation p < .01). Young subjects had significantly more task-unrelated thoughts than older, regardless of sleep condition.

Task-unrelated thoughts correlated with errors of omission (r = 0.65, p < .001). Also, including task unrelated thoughts as covariate in the age * sleep deprivation ANOVA, main and interactions effect of age and sleep deprivation were no longer significant.

Reaction time was significantly slower in older adults, but no main or interaction effect of sleep deprivation occurred. Errors of commission were not affected by condition.

Conclusions: The results show that sleep deprivation caused both mind wandering and poorer task performance in young but not older participants. In addition, mind wandering rates correlated with errors of omission, which may indicate that a diminished ability to shut down off-task thoughts after sleep deprivation could be an important pathway to performance decrements after sleep loss. In line with previous research, mind wandering appears to occur less frequently in older individuals compared with younger. This lower occurrence of mind wandering in older subjects may potentially enable them to better maintain performance after sleep deprivation and partially explain the higher resilience of older adults to sleep deprivation.