Neuroticism, prediction of mood, and 5-HT function

• Main Author: Stewart, M. E.
• Published: University of Edinburgh 2002
• Subjects: 155
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.662471

Two personality traits, Neuroticism and Extraversion can be reliably extracted from self-report personality questionnaires, whether the questionnaire has been devised from animal behavioural models, psychiatric observation or from adjectives found in the English (or other) language. Neuroticism correlates positively with low mood, Extraversion with high mood in healthy volunteers. Scores on personality factors, such Neuroticism (from the Eysenck Personality Questionnaire), are increased in unipolar depressed patients. Harm Avoidance and Neuroticism are highly correlated. Cloninger (1987) suggests that Harm Avoidance is related to brain serotonin mechanisms. Affective disorders and function of the 5-HT system have been linked through (1) clinical patients recovered from depressive disorder. The central hypothesis of this study is that high scores on the personality trait Neuroticism predispose to depressive mood changes following tryptophan depletion. Individuals who scored at the extreme ends of this scale were selected from a sample of 1031 volunteers to be compared in a case control design. Analysis of the whole sample confirms that Neuroticism and Extraversion can be extracted from Eysenck’s Personality Questionnaire-Revised (EPQ-R) alone and from the EPQ-R and the Tri-dimensional Personality Questionnaire (TPQ) when combined, in a sample of 897. Furthermore, Harm Avoidance and Neuroticism positively correlate with low mood measured by the Total General Health Questionnaire-28 (Spearman’s rho=.548, n=899, p<.01 and .515, n=899, p<.01 respectively), and Extraversion correlates with high mood measured by the Oxford Happiness Inventory (Pearson’s r=.495, n=896, p<.01). Participants who scored at the extreme ends of the Neuroticism scale (17 high and 15 low scorers) took part in a controlled double-blind cross-over study of tryptophan depletion. Before and 5 hours after amino-acid drinks a detailed assessment of mood, neuropsychological function and resting EEG was carried out. Scores on Neuroticism scale did not predict mood change. The effect size for change on the Befindlichskeitskala (a self-report mood measure sensitive to clinical change) between depletion and non-depletion days compared between high and low scorers was 0.39. This means that 210 subjects will be required to achieve a power of 80% with a two-tailed alpha of p<0.05. Neuroticism is, therefore, not an important predictor of individual serotonergic function in healthy volunteers, as assessed by tryptophan depletion.