Circadian misalignment and cognitive flexibility in night shift workers.
Cheng P, Tran M, Tallent G, Pillai V, Cuamatzi A, Bazan L, Moss K, and Drake CL. Circadian misalignment and cognitive flexibility in night shift workers. Sleep 2016; 39:A173.
Circadian misalignment can impact health and performance, and is of particular concern for shift workers, whose work schedules may be at odds with their endogenous sleep-wake rhythms. Impairments in cognitive performance have been observed as a result of circadian misalignment; however, these observations have been limited generally to vigilance and reaction time. Less is known regarding on-task cognitive performance. The task-switching paradigm is often used to measure executive control of cognition, particularly in attentional flexibility. In this paradigm, trials involving varying task-rules are completed in quick succession. Some trials employ the same taskrule as the previous trials (“repeat” trials), whereas others employ a different task-rule (“switch” trials). Switch trials require the individual to cognitively switch task-rules, and therefore should result in longer reaction times compared to repeat trials (i.e., “switch cost”). Larger switch costs are indicative of increased effort in set switching, and therefore reduced cognitive flexibility. Successful task-switching performance also requires adequate inhibition of prior task rules, which can be measured by reaction time on trials returning to the same taskrule after a switch trial, compared to performance following successive switch trials (i.e., “set inhibition”). Methods: Twenty-one permanent night shift workers (13 female) participated in a larger study examining the consequences of circadian misalignment on health. Circadian phase was evaluated using dimlight salivary melatonin onset (DLMO). DLMO at or after 6am was considered full circadian alignment. Cognitive flexibility was evaluated using a computerized task-switching paradigm. Results: A multiple linear regression indicated that switch-costs increased linearly with increasing circadian misalignment due to earlier DLMOs (β = .54, p < .01), controlling for sex and age as covariates. No significant effect was detected with set-inhibition. Conclusion: Results indicate that cognitive flexibility is related to circadian alignment, with better alignment associated with increased flexibility. This offers further insight into the cognitive vulnerabilities related to circadian misalignment that may impact risk for errors, accidents, and injuries, particularly for shift workers