Who is pre-disposed to insomnia? A psychobiological investigation

It has been hypothesised that a trait-like vulnerability to sleep disruption exists. This has been demonstrated in response to physiological stressors such as caffeine and phase advance. From this work the Ford Insomnia Responsivity to Stress (FIRST) questionnaire was designed, which aims to specify those who are vulnerable to stress related sleep disruption. Further to this, neuroticism and emotion focused coping have been shown to characterise the insomnia population, and suggested that these constitute risk factors for the development of an insomnia syndrome. However, there has been very little work which aims to define an at-risk population and none which aims to characterise this population from both a physiological and psychological perspective. The aim of this thesis is to define the vulnerable population with regards to psychology and psychobiology. . It was hypothesised that the vulnerable group would show greater stress reactivity, physiologically, higher levels of neuroticism relative to the resilient group, lower levels of conscientiousness and a greater inclination toward rumination and worry. Over three studies measures of sleep, personality, stress perception and coping styles amongst others were taken as well as measuring, separately, 3 indices of physiological stress response: Cortisol output: Salivary free cortisol was taken whilst a sample of good sleepers completed the Trier Social Stress Test (TSST) (n=32). Results indicate that the vulnerable group show significantly greater levels of cortisol at base line (p<0.05).This was mediated by conscientiousness (β=0.39). They were also higher in negative affect, rumination, stress and worry (p<0.05).The vulnerable group also showed an increase in insomnia symptoms in response to real life stress. This was also related to conscientiousness (r= 0.55, p<0.05) Cardiovascular response: Heart Rate (HR) and Cardiac Vagal Tone (CVT) were measured while participants (n=31) completed a relaxation (baseline) and stressful task. There was found to be a main effect of group on HR response to the stress task relative to baseline, but this did not maintain when psychological variables of interest were entered (n=31) into the model. Conscientiousness was related to lower CVT change, interpreted as lower CVT flexibility. Psychologically, the vulnerable group were again found to score higher on neuroticism, perceived stress and rumination relative to the resilient group (p<0.05). Brain activation: fMRI data was collected whilst participants completed a stroop task, in which a siren indicated an increase in task difficulty (stress cue) (n=24). It was found that the vulnerable group showed significantly less activation bilaterally in the inferior parietal lobule (IPL) (p<0.001). In the left IPL activation was mediated by neuroticism (β=0.607).There was also significantly greater activation in the left postcentral gyrus (PG) (p<0.001), compared to the resilient group. This was mediated by FIRST score (β=-0.61). Again, the vulnerable group scored higher on measures of neuroticism and lower on conscientiousness (p<0.05). Psychometric information gathered across the 3 studies was collapsed into one dataset (n=84). ANOVA revealed that the vulnerable group had significantly higher scores on measures of neuroticism, perceived stress, state stress, depressive feelings, depressive thinking, brooding, worry, emotion focused and problem focused coping and significantly lower scores on conscientiousness and extroversion (p<0.05). Results indicate that the vulnerable group are higher on neuroticism across all 3 studies, and score higher on rumination and stress questionnaires in 2 of the studies. Physiological data suggests that the vulnerable group are more sensitive to stress anticipation, as opposed to showing greater reactivity to stress. It is concluded that neuroticism is a risk factor for developing insomnia and that the vulnerable population show greater physiological responses whilst anticipating stress, a phenomena which represents the interaction between personality, rumination and the physiology of the stress system