Sleep Moderates Effects of a Depressive Episode on Response Bias to Emotional Eyes

Abstract

Introduction: Response bias was a tendency to say “yes” or “no” in distinguishing learnt materials from new information. Depressive individuals, even remitted, were reported to be biased in recalling negative experience. While poor sleep was shown to be associated with depressed mood, its role in emotion-modulated cognition (including response bias towards emotional stimuli) in depressed individuals remained to be determined. Methods: A community sample (n = 81, 32 males, aged 17-25, nonmedicated) was recruited and interviewed according to the structuralclinical- interview for DSM-IV disorders. Sixteen participants reported a depressive episode (depressive-episode group) in the lifetime, and the rest formed the control-group. Both groups completed a five-day sleeplog and emotional recognition memory task of positive, neutral and negative eyes. There was a learning- and testing-phase, separated by either a 90-minute polysomnography-monitored nap or wakefulness. Response bias (c’) was calculated following signal detection theory, with a negative c’ representing tendency to say “yes”, and positive c’ for “no”. Results: The depressive-episode and control-group were matched on demographics and sleep duration (ps > .05). A factorial design with two between-subject factors (depressive-episode and nap-condition) revealed a significant main effect of depressive-episode on positive eyes c’, F(1,72) = 5.74, p = .019, indicating more negative c’ towards positive eyes. Depressive-episode interacted with nap-condition on c’ of positive, F(1,72) = 4.432, p = .039, and negative eyes, F(1,72) = 5.895, p = .018. Post-hoc analyses (Mann-Whitney U test) showed that among the depressive-episode group, napped individuals had significantly more negative c’ on positive (p = .049) and negative eyes (p = .026). Among controls, there were no differences between the napped and wake individuals (ps > .05). Conclusion: Sleep was found to moderate the effects of depressive episode on response bias in emotionally-charged eyes: following a nap, individuals with depressive episode had a higher tendency to say “yes” to both positive and negative eyes, suggesting that sleep may facilitate recognition of both positive and negative information in individuals with depressive episode.