Changes in structural aspects of mood during 39e66 h of sleep loss using matched controls J.L. Paterson a, * , J. Dorrian a , S.A. Ferguson a , S.M. Jay a , N. Lamond a , P.J. Murphy b , S.S. Campbell b , D. Dawson a a Centre for Sleep Research, University of South Australia, GPO Box 2471, Level 7, Playford Building, UniSA City East Campus, Frome Road, Adelaide SA 5000, Australia b Laboratory of Human Chronobiology, Department of Psychiatry, Cornell University Medical College, 21 Bloomingdale Road, White Plains, NY 10605, USA article info Article history: Received 1 February 2010 Accepted 15 June 2010 abstract A number of studies have described mood change during sleep loss in the laboratory, however, an understanding of fluctuations in structural aspects of mood under such conditions is lacking. Sixty-two healthy young adults completed one of three possible conditions: one (n ¼ 20) or two (n ¼ 23) nights of sleep loss or the control condition which consisted of one (n ¼ 9) or two (n ¼ 10) nights of 9 h time in bed. The Mood Scale II was completed every two waking hours and data were analysed in terms of the frequency and intensity of mood reports. Overall, sleep loss conditions were associated with significantly less frequent happiness and activation and more frequent fatigue reports (p < 0.001). Intensity was also significantly reduced for activation and happiness, and increased for depression, anger and fatigue (p < 0.05). Interestingly, there were no significant differences in anger following two nights in the laboratory with or without sleep. Further, two nights in the lab with normal sleep was associated with significant increases in depression intensity (p < 0.05). Findings support the hypothesis of a mood regulatory function of sleep and highlight the relative independence of frequency and intensity and of positive and negative mood dimensions. Findings also suggest that the laboratory environment, in the absence of sleep loss, may have a significant negative impact on mood. Ó 2010 Elsevier Ltd and The Ergonomics Society. All rights reserved. 1. Introduction Negative mood change during sleep loss has been well docu- mented (e.g., Brendel et al., 1990; Mikulincer et al., 1989). However, the frequency and intensity of such mood change has received considerably less attention. Diener and Emmons (1985) have argued that in order to wholly understand affective experience, it is necessary to examine the so-called structure of affect, rather than simply global, or momentary, well-being. These authors maintain that a complete understanding of mood change requires not only assessing the frequency with which positive and negative mood is experienced, but also the intensity with which it is expressed. For example, one individual may experience anger frequently but not intensely, whilst another may experience anger relatively rarely but more strongly (Schimmack and Diener, 1997). Diener et al. (1985) applied their study of affective structure during normal daily activities and found intensity and frequency of positive and nega- tive mood to be consistent within persons, but independent from each other. The authors proposed that individuals are consistent in terms of mood, and that frequency and intensity constitute inde- pendent dimensions which combine to form overall mood expe- rience. Within the framework of sleep loss studies, however, this more in-depth understanding of affective experience is lacking. Many laboratory-based sleep studies are conducted with the intent to apply findings to shift working populations. In this way, changes in cognitive and psychomotor performance as a result of sleep loss have been thoroughly examined due to their implications for safety and effective functioning (e.g., Durmer and Dinges, 2005). The effects of mood on performance and, in turn, safety is also beginning to receive more attention (e.g., Franzen et al., 2008). Indeed, it is evident that negative mood can have a significant impact upon a constellation of neurobehavioral functions relevant to shift work, ranging from simple reaction time (Bolmont et al., 2000) to logical reasoning (Oaksford et al., 1996) and memory consolidation (Bower, 1981). Mood also has implications for general health and well-being. Haack and Mullington (2005) have proposed that negative mood may contribute to an individual’s experience of pain and may negatively affect health in general. On the other hand, positive affect has been associated with greater resistance to the common cold (Cohen et al., 2003), and even with decreased risk of * Corresponding author. Tel.: þ61 8 8302 2894 (office), þ61 431 839 005 (mobile); fax: þ61 8 8302 6623. E-mail address: jessica.paterson@unisa.edu.au (J.L. Paterson). Contents lists available at ScienceDirect Applied Ergonomics journal homepage: www.elsevier.com/locate/apergo 0003-6870/$ e see front matter Ó 2010 Elsevier Ltd and The Ergonomics Society. All rights reserved. doi:10.1016/j.apergo.2010.06.014 Applied Ergonomics 42 (2011) 196e201