Assessing Latent Inhibition Deficits in Youth At-risk of Conversion to Psychosis

Abstract

In recent years there has been much interest in the psychosis prodrome, the period that directly precedes the onset of psychotic illness. Past research has found that prodromal individuals demonstrate various neurocognitive deficits when compared to healthy individuals. Despite being well studied in patients with schizophrenia little or no research has examined Latent Inhibition (LI), a cognitive phenomenon where simple exposure to a stimulus without pairing to a consequence lowers the future associability of that stimulus to events, in at-risk individuals. As LI is sensitive to fluctuations in dopamine levels, it has potential as a method for detecting disrupted dopaminergic systems. This thesis describes the use of a novel LI paradigm to investigate LI deficits in individuals who have been identified to be at Ultra High Risk (UHR) of transition to psychosis.

Three studies are described in this thesis. Study 1 attempted to validate the novel LI paradigm for use in an Asian population taking into account cigarette smoking as a mediating variable of dopaminergic level and thereby LI. Sixty healthy participants (30 smokers and 30 non smokers) were tested. No significant differences in reaction times were found between the Pre-Exposed (PE) and Non Pre-Exposed (NPE) conditions in either group. However, the data showed that some participants showed a LI effect regardless of smoking status. Study 2 was conducted to determine what influenced participants? performance on the LI task. The LI paradigm was administered on 109 healthy participants, and their strategies in approaching the task were collected. The results show that the strategy reported by participants significantly influenced the results. Only when participants utilized one particular strategy (dubbed the Optimal strategy) did they show a LI effect. In Study 3, 52 participants who met UHR criteria were tested with the LI paradigm, and their strategy information was collected. The results showed that even in the group which utilized the ?Optimal? strategy, there were no differences between PE and NPE reaction times. This indicated the absence of a LI effect. The findings are consistent with prior research on LI in individuals with schizophrenia, and the results provide support for the possibility of a disrupted dopaminergic system in UHR individuals.