The first part of the thesis explored the pattern of emotional reactivity amongst individuals with Borderline Personality Disorder (BPD). A previous review (Rosenthal, Gratz, Kosson, Cheavens, Lejuez & Lynch, 2008) claimed that a discrepancy exists in the subjective versus objective patterns of responding to emotional stimuli in those with BPD. The present review assessed the reliability of such findings by reviewing a more homogenous sample of studies that had used similar methodological procedures, in addition to a range of subjective and objective measures. It also aimed to investigate psychophysiological factors associated with this proposed divergent pattern of responding. The methodological quality of all included studies was assessed. The evidence reviewed disputes claims that BPD individuals display diminished physiological reactivity, despite equal or higher self-reported emotional reactivity than controls. Instead, the present review found that individuals with BPD react more severely (both psychologically and physiologically) to experimental stimuli, than controls, particularly when the stimuli is personally-relevant. Disruption of specific brain structures involved in the regulation of emotion within the Autonomic Nervous System (ANS) are implicated in this heightened profile of emotional reactivity. Furthermore, present state dissociation acts as a defence mechanism which appears to limit cognitive processing abilities such as problem-solving, attention and concentration in those with BPD. The second part of the thesis described a randomised controlled study investigating the effects of an attention training technique on pain tolerance. The Attention Training Technique (ATT; Wells, 1990) is a brief technique used in metacognitive therapy to modify attentional control. The effect of ATT versus Progressive Muscular Relaxation (PMR) on pain tolerance was examined in a sample of individuals who had experienced early childhood trauma (N=57). Participants were randomly assigned to either the ATT condition (N = 29) or the PMR condition (N = 28). A laboratory stressor was included: The Cold Pressor Task (CPT) as an objective measure of pain tolerance. Results supported the hypothesis that ATT modified performance on the CPT. Individuals assigned to the ATT condition were able to persist significantly longer with the CPT than those in the PMR condition. Theoretical and clinical implications of the findings are discussed. Results provide preliminary evidence for the possible benefits of ATT within medical settings.The third part of the thesis critically reflected on the methodological issues and dilemmas presented by the systematic review process, as well as the methodological and ethical issues raised by the research study.