The role of sleep deprivation in the expression and reduction of fear
Prospective evidence suggests that sleep disturbances lead to the development of anxiety-related disorders. Since such prospective evidence does not allow any conclusions concerning causality, experimental research is needed. The present dissertation was aimed at experimentally probing the role of sleep deprivation in the expression and reduction of fear in healthy participants. In Chapter 1, we investigated the effects of sleep deprivation on fear expression. We tested this by using a fear conditioning procedure with a learning phase in the evening and a test of fear expression in the subsequent morning. Between the learning phase and the fear expression test, participants were either kept awake or had a regular night of sleep. Fear expression, as indexed by outcome expectancies, was enhanced after a night of sleep deprivation. Since this study design could not disentangle whether the observed effect was due to sleep deprivation after learning or the sleep-deprived state at test, we conducted two follow-up studies. These studies are reported in Chapter 2 and manipulated sleep deprivation after learning (Study 1) and before testing (Study 2) separately. Contrary to our expectations, neither study found an effect of sleep deprivation on fear expression. Apart from fear expression, we also examined the effect of sleep deprivation on the reduction of fear by including an extinction phase in these studies. While sleep deprivation after learning led to overall lower outcome expectancies during the extinction phase in Study 1 (be it only in the full sample and not in a subsample that adhered to a stricter sleep regime), we found no effect of sleep deprivation when it occurred before extinction learning in Study 2. In Chapter 3, we developed and tested a novel fear conditioning procedure in two separate studies. This procedure allows to study mere thinking of the aversive outcome. Given that previous research has shown that unpleasant thoughts of an aversive event are associated with sleep disturbances, this procedure could become a valuable tool in future sleep research. When considering the prospective evidence, it is somewhat surprising that our studies did not consistently find an effect of sleep deprivation on fear expression in the laboratory. The general discussion addresses possible reasons for this. More precisely, we review other pathways from sleep disturbances to pathological anxiety than the ones we tested and discuss the external validity of the experimental procedures that we used to model disturbed sleep and anxiety-related disorders in the laboratory.