Date of Award

Fall 2012

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Neuroscience

Supervisor

Henry Szechtman

Co-Supervisor

Erik Woody

Language

English

Committee Member

Louis Schmidt

Abstract

We present the results from a series of experiments which support a novel hypothesis for a special motivational circuit underlying both the detection and response to potential threat, and the typical symptoms of Obsessive-Compulsive Disorder (OCD). Szechtman and Woody (2004) proposed that the Security-Motivation System (SMS) has two primary responsibilities: surveillance of the environment for subtle cues that may indicate the potential for danger, and motivation towards avoidance of this harm through participation in appropriate behavioural motor programs. To determine the parameters under which the SMS operates, we designed and implemented several novel paradigms for examining both typical and atypical response of the SMS to potential threat in a number of populations. It was demonstrated that the SMS is specifically activated after exposure to cues that suggest the possibility of harm to the self or others, such as via threats to personal safety or contaminated objects. Once activated, the SMS can only be disengaged through participation in the appropriate motivated corrective behaviour – such as hand washing or checking for danger. Results showed that this essential termination feedback cannot be substituted with cognitive strategies, and that in the absence of these behaviours, activation of the SMS persists; the consequence of incomplete SMS termination strongly resembles the stereotypic compulsions in OCD. Indeed, results demonstrated that patients with OCD are unable to achieve satisfaction from task completion after corrective behaviour, resulting in continued SMS activation, after exposure to stimuli specific to the patients’ symptom profile. Our collective results provide a solid foundation for the view of OCD as a dysfunction of Security-Motivation, and indicate that the SMS is indeed an essential circuit for potential threat detection.

McMaster University Library