Journal of Affective Disorders 72 (2002) 281–289 www.elsevier.com / locate / jad Research report Is weakened circadian rhythmicity a characteristic of neuroticism? * Greg Murray , Nicholas B. Allen, John Trinder, Helen Burgess Department of Psychology, University of Melbourne, Parkville, Victoria 3052, Australia Received 19 June 2001; accepted 23 November 2001 Abstract The aim of this study was to undertake a preliminary investigation of the novel hypothesis that weakened circadian rhythmicity is an aspect of the psychobiology of neuroticism (N). Two groups of subjects [young healthy females categorised as High N (N 5 8) or Low N (N 5 6)] were compared in terms of a classical circadian variable (the unmasked rhythm in core body temperature), and a validated psychological variable (diurnal rhythm in Positive Affect), under two experimental protocols (constant routine and ambulatory). As predicted, model-fitting analyses found that the High N group was characterised by attenuated circadian amplitudes in unmasked body temperature under both protocols. Also as hypothesised Positive Affect exhibited a circadian rhythm that was only significant in the Low N group. A stronger synchronisation between the biological and psychological rhythms was also observed in the Low N group. Results are discussed in terms of the implications of a possible circadian diathesis for disorders and complaints across the neurotic spectrum.  2002 Elsevier Science B.V. All rights reserved. Keywords: Neuroticism; Circadian rhythmicity; Depression; Positive affect 1. Introduction function (Akiskal, 1991; Depue et al., 1989). This reasoning was applied in the current project to Personality can be understood as mediating remote develop the novel hypothesis that weakened circa- predisposing and proximate precipitating factors in dian rhythmicity might be an aspect of the psycho- affective illness (Akiskal, 1991). From this point of physiology of the general vulnerability trait neuro- view, it is commonly argued that there is a con- ticism (N). tinuum in affective difficulties, and that a similar Neuroticism is a prominent dimension in almost continuum might exist at the level of physiological all major models of personality structure, including Eysenck’s (Eysenck and Eysenck, 1985), Zuckerman’s (Zuckerman, 1995) and Costa and McCrae’s Five Factor Model (FFM: Costa and *Corresponding author. Fax: 1 61-3-9349-4195. E-mail address: g.murray@psych.unimelb.edu.au (G. Murray). McCrae, 1992). Sensitivity to threat is the tem- 0165-0327 / 02 / $ – see front matter  2002 Elsevier Science B.V. All rights reserved. PII: S0165-0327(01)00465-7