صبحگاهی-شبانگاهی و افسردگی: شواهد اولیه برای نقش سیستم فعال سازی رفتاری و عاطفه مثبت

There is considerable evidence of circadian rhythm abnormalities in mood disorders. Morningness–eveningness, the degree to which people prefer organizing their activity and sleep patterns toward the morning or evening, is related to circadian phase and is associated with mood, with relatively greater psychological distress among evening types. Given that circadian rhythms may also relate to the Behavioral Activation System (BAS) and positive affect (PA), but not to the Behavioral Inhibition System (BIS) or negative affect (NA), it was hypothesized that individual differences in BAS sensitivity and levels of PA, but not BIS and NA, would explain the association between morningness–eveningness and depression in a sample of 208 individuals with a range of depressive symptomatology. As predicted, increasing eveningness was associated with greater depression, lower BAS, and lower PA, but not directly associated with NA. Path analyses supported a model wherein morningness–eveningness is associated with depression via multi-step indirect paths including BAS-Reward Responsiveness, PA, and NA. A path between BIS and depression was distinct from the one involving morningness–eveningness. A variety of alternative path models all provided a weaker fit to the data. Thus, results were consistent with the BAS and PA mediating the effects of morningness–eveningness on depression.

More than three decades of research provide compelling evidence of circadian rhythm abnormalities in mood disorders (e.g., Wirz-Justice, 2005). Researchers have advanced a number of hypotheses attempting to relate the circadian abnormality to the other symptoms, including the ‘phase advance hypothesis’ (early morning awakenings and reduced REM latencies are due to short circadian periods), the ‘blunting hypothesis’ (reduced amplitudes in a number of circadian rhythms during the depressed phase that normalize upon remission), and the phase-shift hypothesis (PSH; delayed rhythms during winter for individuals with Seasonal Affective Disorder) among others. Although none of these have garnered unequivocal empirical support, tantalizing hints at the circadian-mood disorder link continue to emerge, ranging from the antidepressant effects of circadian-based treatments (e.g., bright light therapy) to preliminary evidence of polymorphisms in genes that influence the circadian cycle in patients with bipolar disorder (Mansour et al., 2005a). An individual difference in circadian rhythms that is potentially important to understanding mood disorders is the degree to which individuals prefer organizing their activities closer to the morning or evening. Based on diurnal preference, or morningness–eveningness, people can be divided into chronotypes (i.e., “larks” and “owls”) with demonstrated differences in sleep–wake patterns and a variety of circadian rhythms, behavioral rhythms such as performance and exercise, and diurnal variation of mood (Kerkhof, 1998). Morningness refers to those who show extreme preferences for daytime activity; in these individuals, peak performance and alertness is associated with the early-morning hours. The opposite is true for those who show eveningness, or extreme preferences for nighttime activities; in these individuals, heightened alertness and peak performance is linked to the evening hours. Chronotypes also appear to differ in less intuitive areas such as personality (e.g., Larsen, 1985), school achievement (Giannotti et al., 2002), general health (Paine et al., 2006), and lifestyle regularity (Monk et al., 2004). Diurnal preference is typically assessed via subjective self-report questionnaires. These measures, which all provide a score that can be left as a continuous scale or assigned to a category (e.g., Definite Evening-type, Intermediate type, etc.) show moderate-to-large correlations with circadian phase using well-validated physiological markers such as melatonin and core body temperature (Bernert et al., 2006). Consequently, some studies have used self-reported morningness–eveningness as a proxy for circadian phase (e.g., Murray et al., 2005). Based on the original Horne and Östberg (1976) scoring criteria, epidemiological studies indicate that 50–60% of the population are morning-types, 2–6% are evening-types,1 and the rest fall in between these two extremes (Taillard et al., 2004 and Paine et al., 2006). Also, morningness appears to increase with age (e.g., Paine et al., 2006 and Monk and Kupfer, 2007). Despite demonstrations of the relationship between diurnal preference and physiological, behavioral, and psychological processes, few studies have looked directly at the association between diurnal preference and mood disorders. Drennan et al. (1991) investigated differences in Horne–Östberg morningness–eveningness scores between depressed (per DSM-III-R criteria) outpatients and age- and sex-matched healthy controls. They found a significantly lower mean score (greater eveningness) in the depressed sample compared with the controls. Building on this work, Chelminski et al. (1999) examined diurnal preference and psychometrically defined “depressiveness” in a large sample of college students. They defined “depressiveness” as scoring in the depressed range of at least two out of three depression scales (Beck Depression Inventory (BDI); Geriatric Depression Scale-Short Form (GDS-SF); and the Center for Studies Depression Scale (CESD)). Using this criterion, they found significant negative correlations (r ≈ − 0.18) between the Horne–Östberg questionnaire and responses on all three depression measures (i.e., greater eveningness was related to greater depression) and a significantly higher incidence of evening-types among the “depressive” students. The mechanisms underlying the association between eveningness and depression remain unknown. The circadian literature has generally focused on physiological or strictly chronobiological mechanisms in attempting to explain the link between mood disorders and circadian abnormalities, thereby neglecting some of the promising ideas to emerge from psychological literature. For example, Watson and colleagues have argued that the absence of positive affect (PA) is relatively specific to depression, thus distinguishing it from anxiety, which shares depression's characteristically high negative affect (NA; reviewed in Watson, 2000). Other formulations suggest that depression involves both an underactive Behavioral Activation System (BAS; also referred to as a Behavioral Approach System or Behavioral Facilitation System), leading to diminished appetitive motivation and decreased PA, and a hyperactive Behavioral Inhibition System (BIS), resulting in increased NA (Fowles, 1994). Integrating the circadian and psychological literatures has the potential to elucidate the connection between chronobiological factors and mood dysregulation. Furthermore, accumulating evidence suggests that PA varies according to a circadian rhythm, but that NA fails to show a systematic daily variation (Clark et al., 1989, Thayer, 1989, Wood and Magnello, 1992 and Murray et al., 2002). Watson (2000) proposed that the circadian PA variation is a manifestation of activity in the underlying BAS, which promotes engagement with the environment during optimal times for reward (i.e., daytime). In contrast to asserting an adaptive basis for the circadian control of appetitive motivation and PA, the model posits that NA lacks systematic circadian variation because it is the manifestation of a reactive BIS responding to aversive or ambiguous stimuli. Thus, systematic variations in BAS may have adaptive functions in terms of motivating organisms toward goal-seeking activities at optimal times, whereas an endogenous variation in BIS would not clearly be adaptive. The present study attempted to integrate these previous findings and theoretical models by examining the association among diurnal preference, motivational systems (BAS and BIS), and affect (PA and NA) in an adult sample with a wide range of depressive symptoms. It was hypothesized that diurnal preference (as a proxy for circadian phase) would be related to BAS sensitivity and PA, but not to BIS sensitivity or NA. It also was predicted that greater eveningness would be associated with lower BAS sensitivity and lower levels of PA. Finally, this work investigated whether BAS sensitivity and PA would statistically explain the relationship between diurnal preference and severity of depressive symptoms.

The findings reported in this study identify multiple explanatory pathways in the associations between diurnal preference and mood disturbance. Notably, the results support a mediating role for BAS and PA in a model with eveningness predicting greater depressive symptom severity. This is the first investigation to test the directionality of effects between morningness–eveningness, PA, and a BIS–BAS model, particularly using a confirmatory factor-analytic approach. To further examine causality, longitudinal studies will be necessary to replicate and build upon these preliminary findings. With regard to the clinical significance of the present study, these results may warrant further research specifically aimed at examining whether previously-established chronotherapeutic approaches (e.g., advancing the sleep–wake schedule; Wirz-Justice and Van den Hoofdakker, 1999) show benefits (with unique effects on PA) for evening types with depressive symptomatology. Likewise, although further research using physiological measures is necessary, by implicating reward processes the findings point towards a potentially fruitful direction for the development of novel pharmacological interventions. For example, medications that selectively target the mesolimbic dopamine system might be particularly beneficial for depressed evening types. Finally, given the apparent interaction of circadian and reward processes, one might speculate that social rhythm therapy (Frank, 2007) might be a useful approach to reducing depression in evening types by encouraging stable daily rhythms of sleep and positive reinforcement.