پاسخ کورتیزول بیداری و ابعاد پنج عامل بزرگ شخصیت

The present study investigated the association between the big five personality dimensions and the cortisol awakening response (CAR), a physiological parameter reflective of HPA axis activity. One hundred and seven participants completed the big five inventory (BFI; John, Donahue, & Kentle, 1991) and collected salivary cortisol samples at 0, 30, and 60 min after awakening on a weekday morning. The cortisol awakening response under the curve (CARauc) and the cortisol awakening response with respect to increase (CARi) were used as outcome variables in the statistical analyses. Hierarchical linear regression analyses were conducted using the data of 92 participants. Gender and age were included as covariates in block one of the regressions, followed by the personality dimensions in block two. Extraversion emerged as a significant predictor of CARauc. No other personality dimensions were significantly predictive of CARauc or CARi. Interestingly, gender emerged as the strongest predictor in the CARauc, with females exhibiting greater cortisol release across the awakening period than males. Our results suggest that extraversion and gender may be particularly important variables to consider in the regulation of the HPA axis.

Cortisol is widely regarded as an accurate measure of hypothalamic–pituitary–adrenal (HPA) axis activity. It is released in response to an acute stressor (Kirschbaum & Hellhammer, 1994), but it also follows a diurnal pattern with production sharply increasing 20–45 min after awakening and then decreasing throughout the day (Clow et al., 2004 and Pruessner et al., 1997). This distinct rise in cortisol during the awakening period is referred to as the cortisol awakening response (CAR). While measurements of cortisol responses to specific stressors in the laboratory provide information on HPA reactivity, the CAR provides insight into the general functioning of the hypothalamic–pituitary–adrenal (HPA) axis (Clow et al., 2004). Therefore, the CAR is an important physiological parameter to consider in relation to long-term stress, health conditions, and psychological traits (Chida and Steptoe, 2009, Fries et al., 2009, Kudielka and Kirschbaum, 2003 and Wüst et al., 2000b). Individual differences in the CAR have been reported across a variety of studies (e.g., Almeida et al., 2009, Pruessner et al., 1999 and Schulz et al., 1998), thus highlighting the need to study psychosocial and environmental influences possibly linked to systematic variations in cortisol release across the awakening period. In terms of studying the individual differences in the CAR, the big five personality theory provides an appropriate theoretical framework; the big five theory has been widely studied in relation to health and well-being (e.g., Friedman et al., 2010 and Jerram and Coleman, 1999), and there is also some evidence for a biological basis for the five factor model (DeYoung et al., 2010). Notably, neuroticism has been associated with both negative mental and physical health outcomes (see Lahey, 2009). Conscientiousness, on the other hand, has been linked to positive health behaviors, overall well-being, and longevity (Hill, Turiano, Hurd, Mroczek, & Roberts, 2011). Especially considering the role HPA axis regulation may play in the maintenance of health and well-being (e.g., Pruessner et al., 2010), further understanding physiological correlates of the big five personality dimensions remains an important research endeavor. An elevated CAR has been positively associated with neuroticism (Portella et al., 2005), and related traits, including negative affectivity (Polk, Cohen, Doyle, Skoner, & Kirschbaum, 2005) and hopelessness reactivity (van Santen et al., 2011). However, there have been some mixed findings in this area of research; Walker, O’Connor, Schaefer, Talbot, and Hendrickx (2011) reported a negative association between the CAR and trait anxiety, and Thorn, Hucklebridge, Evans, and Clow (2009) reported that seasonality, a trait-like variable representing the propensity to exhibit mood changes across the seasons, was negatively correlated with the CAR. There has been some research on the relationship between the CAR and extraversion. Recently, van Santen et al. (2011) reported a trend association (p = .10) between extraversion and flatter CAR levels. In contrast to this finding, Hauner et al. (2008) previously reported an association between introversion (i.e., low extraversion), as measured by the Eysenck Personality Inventory, and low CAR levels among both male and female adolescents. Previous research has also suggested no association between morning salivary cortisol and extraversion ( Munafò et al., 2006). Overall, research suggests that there is little consensus regarding the direction of association between the CAR and extraversion. The literature on personality traits and the CAR, albeit limited, provides conflicting evidence for the association between personality factors and HPA functioning. Aside from the trend association between extraversion and lower CAR levels, van Santen et al. (2011) did not find any other associations between the remaining big five factors and the CAR. It is possible that demographic factors, including age and gender, also contribute to the observed individual differences in the CAR. Females have exhibited greater CAR than males (Almeida et al., 2009, Kunz-Ebrecht et al., 2004 and Wright and Steptoe, 2005), and there has been some evidence to suggest that the magnitude of the CAR may increase with age (Almeida et al., 2009 and Kudielka and Kirschbaum, 2003). For that reason, these demographic variables were also included as covariates in the models of the present study. Based on previous research and theory on personality and CAR, we hypothesized that neuroticism would be positively predictive of CAR and that extraversion would be negatively predictive of CAR. Neuroticism, a trait that encompasses an individual’s propensity to experience negative emotions (Larsen & Buss, 2005), should, theoretically, be linked to an elevated CAR, a physiological marker that seems to be influenced by negative emotional traits and states (Polk et al., 2005 and Portella et al., 2005). Extraversion, on the other hand, is a trait characterized by a high arousal threshold and a need for environmental stimulation (Larsen & Buss, 2005). Therefore, we hypothesized a negative association between extraversion and CAR, in that higher extraversion scores would be associated with a lowered CAR.