City Research Online

Abstract

Prepulse inhibition of the startle reflex (PPI) refers to the reduction of the startle response to a startling stimulus (pulse), when such a pulse is preceded by a stimulus of lower intensity (prepulse). PPI is believed to reflect the working of a sensory gating mechanism, which by limiting excess sensory input, protects information processing. PPI is impaired in psychiatric populations where such inhibitory processes are compromised, including schizophrenia. The excessive rate of smoking seen in people with schizophrenia is thought to reflect an attempt at self-medication. Nicotine increases PPI in animals as well as healthy humans, and combined such observations suggest the possibility that smoking may provide a way of restoring some of the cognitive abnormalities of schizophrenia as indexed by deficient PPI.

This hypothesis was central to the investigations conducted as part of this thesis. The effects of nicotine on PPI were tested in people with schizophrenia and healthy controls. In the first study of its kind the neural correlates of the enhancing effect of nicotine on PPI were studied in both populations using functional magnetic resonance imaging. Similar motivational factors for smoking behaviour in healthy smokers were explored in a longitudinal study of smokers wishing to quit. Finally, a parallel study delved into the psychological significance of PPI by investigating the tenet that PPI reflects an automatic response, a quality particularly useful to schizophrenia research.

Nicotine enhanced PPI in both healthy and schizophrenic subjects. Furthermore the neuroimaging data confirmed this modulatory effect to involve the hippocampus. Startle amplitude, but not PPI, during smoking was found to predict successful smoking cessation in healthy subjects. Finally, supporting evidence was found for the involuntary status of PPI. This thesis lends support to the hypothesis that smoking may represent an attempt to self-medicate symptoms in schizophrenia.

Publication Type:	Thesis (Doctoral)
Subjects:	B Philosophy. Psychology. Religion > BF Psychology R Medicine > R Medicine (General)
Departments:	School of Health & Psychological Sciences > Psychology School of Health & Psychological Sciences > School of Health & Psychological Sciences Doctoral Theses Doctoral Theses

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