Investigating Maladaptive Habit Formation and Threat Influences in Obsessive-Compulsive Disorder
Maladaptive habit formation is hypothesised to contribute to numerous clinical disorders, including Obsessive-Compulsive Disorder (OCD). The way in which habits become maladaptive and persist is not fully understood, but the acquisition of both goal-directed and habit-like behaviour can be captured using a procedure called Pavlovian-Instrumental Transfer (PIT). PIT refers to the influence of previously learned pavlovian stimuli on instrumental action and is commonly used to assess the motivational influences of reward-related cues on behaviour. The current state of human appetitive PIT was examined and used as a framework underpinning the acquisition of maladaptive habits. The PIT procedure was then adapted to capture context-dependent threat influences learning, mimicking OCD symptomology. The wide variety of procedures and experimental designs encompassing many different theoretical interpretations of PIT, became apparent through a systematic literature review on human appetitive PIT experiments, presented in Chapter 3. The disparity in the procedural and theoretical approaches in human PIT studies results in challenges in comparing findings across studies and has implications for the translational relevance of PIT between species. Rodent PIT studies reveal insights into the acquisition and consolidation of reward-based learning in humans, therefore a cross-species comparison to optimise the PIT procedure is a crucial consideration. To both improve the cross-species and clinical translatability of PIT, a series of experiments were conducted to optimise the PIT procedure to capture and further understand maladaptive habit formation and the acquisition of maladaptive behaviour. Chapter 4 considers the relevance of stimulus modality, as PIT procedures in rodents commonly use auditory stimuli - to avoid other potential pavlovian confounds, including pavlovian conditioned approach - but in humans, visual stimuli are more commonly used. This chapter introduces a novel PIT task, used to investigate the role of sensory modality in a reward-oriented appetitive PIT task, comparing how auditory versus visual cues affect the strength of specific and general transfer with food rewards in humans. Both modalities produced strong general and specific PIT, indicating that cue modality does not significantly modulate PIT effects. Chapter 5 extended this research from a healthy participant population to a sample of adolescents with OCD, as part of a larger study investigating differences in behaviour, and neurochemical differences using magnetic resonance spectroscopy (MRS). Both OCD patients and healthy controls showed strong general and specific PIT and revealed no significant between-groups differences. However, as this task was purely appetitive, a subsequent adaptation was considered in Chapter 6 to include an overall aversive context, modelling a potential over-reliance on habitual safety-seeking in OCD patients. To attempt to capture the safety-seeking observed in OCD, Chapter 6 presents a novel PIT task in virtual reality (VR) that fosters appetitive responding in an overall contamination-specific aversive context, much like OCD symptomology (e.g. handwashing to avoid contamination). Following piloting, participants from the general population, stratified for contamination fears, were recruited. These participants were exposed to one of three context-relevant or irrelevant stressors (general threat, contamination-specific threat, or a neutral control condition) in realistic and immersive VR environments, created in collaboration with Microsoft and Xbox-owned video games company Ninja Theory. Stress measures included both salivary alpha-amylase (sAA) and heart rate data collected by photoplethysmography (PPG). Those experiencing a state-stressor prior to the PIT procedure showed significantly increased arousal and stress levels. Correlational analyses were conducted between trait-stress and compulsivity and general and specific PIT. These data indicate that people with high trait compulsivity and anxiety may rely on habit-like processes under stress resulting in differences in specific PIT expression and the persistence of general PIT in such contexts. This research enhances the understanding of maladaptive habit formation in diverse motivational contexts, which can provide insight into the cognitive behavioural profile of OCD.
Behavioural Neuroscience, Compulsivity, Habits, Maladaptive Habits, Obsessive-Compulsive Disorder, Pavlovian, Pavlovian-Instrumental Transfer
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