Event-related brain electrical activity and information-processing in obsessive-compulsive disorder



Degree Name

Doctor of Philosophy (Clinical Psychology)


School of Psychology


This thesis examines brain activity relating to neutral and emotional stimuli in obsessivecompulsive disorder (OCD), using event-related potentials (ERPs), in order to evaluate aspects of dominant neurobiological and cognitive-behavioural models of the disorder. Specifically, the thesis contributes to the understanding of facilitatory and inhibitory aspects of attention, and of attention relating to threatening versus neutral stimuli, in OCD. In Study 1 a novel experimental paradigm to measure both facilitatory and inhibitory aspects of selective attention was designed and evaluated in a sample of healthy individuals (n = 20). Manipulations intended to increase facilitative aspects of selective attention through priming resulted in incremental decreases in RTs and sensory and stimulus discrimination processes indexed by ERP (P1/N1) component latencies. Conversely, manipulations aimed at increasing inhibitory load through negative priming resulted in incremental increases in RTs and ERP (N1, P2 and N2) latencies associated with stimulus discrimination, early attention and inhibitory brain activity. In Study 2, inhibitory and facilitatory processes were investigated in participants with OCD (n = 20), panic disorder (PD; n = 20) and healthy controls (HCs; n = 20). Both anxious groups demonstrated ERP and RT evidence of anomalous priming, inhibitory processing, and attention allocation, which were more severe in OCD than in PD, and which differed between OCD subgroups. Additionally, in OCD alone, stimulus discrimination occurred later as a function of stimulus repetition, suggesting atypical processing of recurrent stimuli. In Study 3, a new experimental paradigm was developed to examine brain electrical activity associated with attention to threat and neutral stimuli. Healthy individuals (n = 20) showed ERP evidence of enhanced neural responses to threatrelated material during a relatively late (P3) stage of information-processing, linked to strategic cognitive and memory processes, interpreted to represent an adaptive, priority processing of salient information in the environment. In Study 4, attention to personally threatening and neutral material was examined in OCD (n = 20), PD (n = 20) and HCs (n = 20). This study provided the first ERP evidence of an attentional bias towards personally threatening material in OCD, in the form of enhanced and prolonged neural responses to threat relative to neutral stimuli during early (P1-N1) stages of information-processing which are generally associated with sensory processing and relatively more automatic, exogenous activity than are later components. An attentional bias towards threatening information was also demonstrated in PD, in the form of ERP evidence of faster processing of threat versus neutral stimuli across several (P1, N2, P3) information-processing stages, accompanied by behavioural RT interference.

Based on these findings it was suggested that: i) deficits in facilitatory and inhibitory aspects of selective attention to neutral stimuli, and anomalies in cortical activity, may contribute to repetitive and intrusive mental phenomena in OCD. These impairments in OCD generally do not differ qualitatively from those in PD, but are more severe, and may differ between OCD subtypes, and ii) that attention to personally threatening information in OCD is associated with intensified and prolonged neural responses during early stages of informationprocessing relative to anxious and healthy controls. Attentional biases are apparent in both OCD and PD, however the nature of the attentional mechanism (slower and enhanced processing in OCD versus earlier capture in PD) may differ between disorders. The implications of these findings for treatment and theoretical models of OCD are discussed.