Methodological differences in Pavlovian fear learning, extinction and return of fear

Examining methodological differences in fear conditioning and extinction studies is a growing area of research, inspired by the recent ‘replication crisis’ in psychological research. Determining whether methodological differences of fear conditioning and extinction paradigms contribute to inconsistent findings is important in terms of the translational value of this paradigm as an experimental analogue of exposure-based cognitive behavioural therapy. The aim of this thesis was to improve the experimental methodology of fear conditioning and extinction studies, by addressing three key questions: 1) Are there parameters of fear conditioning and extinction tasks that differentiate successful from unsuccessful extinction in studies with children and youth; 2) Do different types and combinations of within-phase subjective measures affect within-phase physiological and between-phase measures of fear conditioning and extinction; and 3) Does behavioural memory reconsolidation in the form of cue reactivation with versus without instructions differentially impact extinction and return of fear? Question one was addressed by conducting a systematic review of 35 fear conditioning and extinction studies conducted with children and adolescents (Chapter 2, Ryan et al., 2019). This review revealed that successful extinction was observed in studies that used fear irrelevant shapes (CS) and tones (US) (recommended for all youth) or fear relevant faces (CS) and screams (US) (recommended only for adolescents) as well as those studies that used 8 – 12 CS trials per acquisition and extinction phase. The most commonly used and effective dependent measures were skin conductance responses (SCRs) and subjective ratings of CS valence, fearfulness and arousal. Fear potentiated startle (FPS) was also effective, however less commonly used with children. It was suggested that standard measures be adopted for subjective ratings scales to assist in comparisons across studies. It was recommended that both physiological measures of SCRs and/or FPS be assessed, as well as within-phase subjective measures of US expectancy ratings and CS evaluations and between-phase measures of CS valence, CS arousal and subjective anxiety. Also, additional measures of contingency awareness and US intensity and pleasantness after the conditioning phase was recommended. The review identified unresolved issues and directions for future research to further clarify the most effective designs and measures. The first experimental study (Chapter 3, Ryan et al., 2021) aimed to address one of the issues identified in Ryan et al. (2019) relating to whether different combinations of within-phase subjective measures of US expectancy and CS evaluations would influence skin conductance responses and between-phase subjective ratings of CS valence, CS arousal and subjective anxiety. The fear conditioning and extinction study involved 88 participants aged between 17- 25 years recruited from first year university psychology students. The Control condition (N =22) included the assessment of SCRs and between-phase ratings. Relative to the Control condition, the US Expectancy condition (N= 21) additionally included within-phase US expectancy ratings throughout each phase, the CS Evaluation condition (N = 21) additionally included within-phase CS evaluations, and the All Measures condition (N = 23) additionally included both within-phase US expectancy and CS evaluations. Within-phase subjective measures influenced learning by changes in arousal measured by SCRs, however they did not influence between-phase ratings. Rating the within-phase US expectancy alone resulted in successful conditioning, extinction and extinction retention of differential SCRs. Providing the within-phase CS evaluation alone resulted in successful conditioning but no extinction of differential SCRs although extinction did occur at the end of the test phase. For the control condition (no within-phase measures), there was also no extinction of SCRs that remained until the end of the test phase. Rating both within- phase measures resulted in successful conditioning and extinction of differential SCRs; however, the arousal was elevated compared to other conditions. The All measures condition also had a return of differential SCRs during the test phase. It was concluded that researchers need to consider the aims and objectives of their study because different types and combinations of within-phase subjective ratings may influence the outcomes. The second experimental study (Chapter 4, Ryan et al., under review) investigated a notable methodological difference in behavioural memory reconsolidation studies, in which some studies but not others include instructions before the cue reactivation manipulation. The goal was to determine whether instructions influence extinction and the return of differential fear responses. Participants were recruited from first year university psychology students (N = 109) with an age range of 17 - 40 years. Four conditions tested the role of instructions on cue reactivation by presenting the cue with (CS+ Instruct) and without instructions (CS+ Only) relative to two conditions that controlled for the role of instructions alone (Instruct Only) and no cue or instructions (Control). Participants completed acquisition, extinction and test phases within a single session, using fear relevant dog pictures and an aversive auditory unconditional stimulus (US). Measures included skin conductance responses (SCRs), within-phase US expectancy, between-phase CS evaluations and subjective anxiety. No condition differences were found - all conditions demonstrated extinction retention of SCRs in the test phase. There were also no condition differences in US expectancy ratings within-phase and CS evaluations between-phase. Subjective anxiety ratings also showed no differences between conditions, although fear reduced after extinction for all conditions. The findings found no support for instructions before cue reactivation and no support for behavioural memory reconsolidation. Three general conclusions were drawn from the results of the systematic review and the two experimental studies: 1) Parameters of fear conditioning and extinction tasks can differentiate successful from unsuccessful extinction; 2) Different types and combinations of within-phase subjective measures affect physiological measures of fear conditioning and extinction studies; and 3) Cue reactivation with or without instructions during behavioural memory consolidation does not impact extinction and the return of fear. Future research implications and recommendations are discussed. The findings from the current PhD program of research have methodological implications for future fear conditioning and extinction studies and add to the literature focused on improving scientific rigour and the replication crisis in psychological research.