Investigating trait impulsivity:behavioural and neural differences in a non-clinical population

The aim of this thesis was to conduct a comprehensive investigation of impulsivity, including rapid-response and reward-delay impulsivity dimensions. A behavioural study was conducted to examine the sensitivity of impulsivity measures to differences between low and high impulsivity groups, based on impulsivity questionnaires. Results showed that the proposed measures were sensitive to differences between groups and that combining impulsivity dimensions provided a better predictor of impulsivity level than each dimension alone. We then tested whether a three-factor model of impulsivity, would benefit or not from the inclusion of a psychometric measure of reward-delay. Although results favoured a three-factor model, including the reward-delay psychometric measure did not improve the model fit, and showed that rapid-response and reward-delay impulsivity are two major dimensions which contribute independently to impulsivity. Potential differences in the neural correlates of response inhibition and delay discounting between the two groups were examined using MEG. Results suggested high impulsivity individuals might show an attentional processing deficit, as indicated by smaller M1 components and less alpha suppression in posterior regions in the two tasks. Regarding response inhibition, the M2 component was found to be reduced in individuals scoring high, possibly reflecting less efficiency. The high impulsivity group engaged frontal networks more during the STOP-M3 component only, possibly as a compensatory strategy. Increased preference for immediacy was observed in high impulsivity individuals, as reflected by larger Immediate-M2 amplitudes. Decreased delta and theta band power was observed in high impulsivity individuals, suggesting a possible deficit in frontal pathways involved in motor suppression. Increased delta and theta power were observed in frontal regions in high impulsivity individuals, while beta band power was found to be supressed, suggesting an increased sensitivity towards reward-related cues. The experiments described here illustrated how trait impulsivity relates to differences in the behavioural and neural correlates of cognitive processes