Individual differences in trait anxiety and their relationship to fear learning and responses to aversive stimuli

Fear learning is an adaptive process that ensures the protection and survival of the organism; however, it can turn maladaptive when fear responses are chronically unregulated or overgeneralized to safe stimuli and contexts. Individual differences in personality traits such as trait anxiety have been linked to differences in fear learning and fear regulation. The study of these differences can shed light into the learning mechanisms that may be associated with vulnerability to anxiety and inform prevention and treatment interventions for anxiety. In this thesis, three studies are presented that examine the relationship between individual differences in trait anxiety and conditioned fear responding, as well as responses to aversive unconditioned events. Study 1 examines whether individual differences in trait anxiety are related to variations in fear generalization from a conditioned compound to its unreinforced components and from a conditioned singleton to an unreinforced compound containing this singleton. Study 1 found evidence for both types of fear generalization (as indexed by pupillary dilation and US expectancy ratings) occurring early during learning. However, fear generalization was not modulated by trait anxiety levels. Study 2 investigated whether individual differences in trait anxiety modulated fear conditioned responses during acquisition and extinction when each was conducted over two different contexts, and during extinction recall, conducted 24 hours after extinction. Here, no impact of trait anxiety was observed upon fear conditioned responses at acquisition when it was conducted over two different contexts. Meanwhile, at extinction conducted across two different contexts, low trait anxiety was associated with decreased differential conditioned fear (as indexed by pupillary dilation), while high trait anxiety was associated with increased fear renewal with contextual changes during extinction. At extinction recall, meanwhile, no effects of anxiety and no differential fear recovery were observed. Study 3 examined the impact of trait anxiety on responses to aversive controllable and uncontrollable stimuli, and whether prior experience of control and anxiety impacted responses to subsequent aversive uncontrollable stimuli. Here, although experience of control was associated with a reduced pupillary response to aversive stimulation relative to experience of uncontrollability, anxiety had no effect in modulating these responses. In turn, prior experience of control was associated with decreased pupil responses to aversive uncontrollable stimuli in the high anxious, but not in the low anxious subjects. Interactions of anxiety and the experimental variables were observed in Study 2 and Study 3 only. These results suggested deficits in extinction learning (Study 2) and increased potentiation of aversive responding when primed by an aversive, uncontrollable experience (Study 3), in the high anxious subjects. Failure to observe anxiety effects on fear generalization in Study 1 may have been due to fast learning of the CS-US contingencies, which had a 100% reinforcement rate, and rapid extinction of fear generalization.

Advisor: Bishop, Sonia