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The present study investigated emotional responding in dysphoric individuals. Dysphoric (N = 25) and nondysphoric (N = 29) individuals completed an emotional imagery task, including pleasant, neutral and unpleasant emotional-eliciting scripts. Self-reported valence and arousal, and measures of cardiac autonomic activity were collected during the task. Compared to nondysphoric controls, dysphoric individuals showed a reduced heart rate increase to pleasant scripts. Less vagal withdrawal in response to pleasant scripts was also found in dysphoric, but not in nondysphoric, individuals. Conversely, no differences between groups in autonomic responding to unpleasant scripts and in subjective measures were noted. Overall, our data showed that dysphoria is characterized by blunted cardiac autonomic reactivity in response to positive rather than negative emotional stimuli. The present findings also suggest that the lack of vagal suppression may reflect a reduced sensitivity to positive environmental stimuli, which, in turn, has been implicated in the development of major depression in dysphoric individuals.

1.1. Emotional responding and depressed mood Depression is conceptualized as a disorder of emotion (e.g., Clark and Watson, 1991, Gross and Muñoz, 1995 and Tomarken and Keener, 1998). The key symptoms of depression are a loss of interest or pleasure in daily activities (i.e., anhedonia) and/or an excessive and persistent negative mood and emotions (e.g., sadness), suggesting that impaired emotional responding plays a crucial role in the development and/or the maintenance of depressive symptoms (e.g., Rottenberg, Gross, & Gotlib, 2005). Although the constructs that underlie mood – diffuse feeling states that are not necessarily elicited by specific events or objects (Watson, 2000) – and emotions – action dispositions that prepare the organism to respond adaptively to meaningful stimuli (Frijda et al., 1989 and Lang, 1995) – are distinguishable, they have been typically considered as mutually interrelated (e.g., Rosenberg, 1998). Accordingly, a growing number of studies have examined how depressed mood affects emotional responding. As mood is likely to potentiate like-valenced emotions, persistent and/or excessive negative mood has been hypothesized to potentiate reactivity to unpleasant emotions (i.e., the negative potentiation hypothesis), on the one hand, and to attenuate reactivity to pleasant emotions (i.e., the positive attenuation hypothesis), on the other hand (for a review, see Bylsma, Morris, & Rottenberg, 2008). Consistent with the positive attenuation hypothesis, it has been reported that clinically depressed individuals (i.e., with major depressive disorder, MDD) evaluate pleasant stimuli as less pleasant compared to healthy individuals in the absence of difference for unpleasant stimuli (e.g., Berenbaum and Oltmanns, 1992, Dunn et al., 2004 and Sloan et al., 2001). At the behavioral level there is evidence that facial reactivity in response to pleasant, but not to unpleasant, stimuli is reduced in clinically depressed individuals compared to healthy controls (e.g., Berenbaum and Oltmanns, 1992 and Sloan et al., 2001). Alternatively, the negative potentiation hypothesis postulates that depressed mood is associated with increased reactivity to unpleasant emotions. In line with this hypothesis, it has been found that, compared to healthy controls, depressed individuals are characterized by great electrodermal reactivity in response to a negative scenario (Sigmon & Nelson-Gray, 1992). Similarly, studies examining emotional reactivity in undergraduates scoring high on depression measures (i.e., with dysphoria) have reported greater skin conductance during the presentation of an aversive stimulus (Lewinsohn, Lobitz, & Wilson, 1973) or in response to a negative feedback about personality characteristics (Golin, Hartman, Klatt, Munz, & Wolfgang, 1977). There is also converging evidence that undergraduates with vs. without dysphoria exhibit greater affective potentiation of the eyeblink startle reflex. That is, the eyeblink startle reflex is greater during the viewing of unpleasant stimuli in participants scoring high relative to low on self-report depression measure (e.g., Cook et al., 1992 and Cook et al., 1991). However, studies on clinically depressed patients have reported no affective potentiation of the startle reflex when viewing unpleasant stimuli (e.g., Allen et al., 1999, Dichter et al., 2004 and Kaviani et al., 2004), suggesting that the negative potentiation hypothesis may not generalize to diagnosed depression (e.g., Gotlib, 1984). The limited support for the negative potentiation hypothesis has led to the formulation of a third alternative, known as the emotional context insensitivity (ECI), which postulates that depression is characterized by valence-independent deficits in emotional responding (Rottenberg, Gross, et al., 2005). The ECI hypothesis is based on the assumption that depressed mood states reduce or disrupt the natural tendency of the organism to respond to environmental stimuli, thus biasing the organism against action (Nesse, 2000 and Nesse and Ellsworth, 2009). As a consequence, depressed mood would result in reduced reactivity to pleasant and unpleasant emotional stimuli and therefore in reduced approach- and withdrawal-related behaviors, respectively (e.g., Bradley, 2000). Impaired valence modulation of subjective measures in response to pleasant and unpleasant film clips provided support for the ECI hypothesis ( Rottenberg et al., 2005a and Rottenberg et al., 2002). Specifically, it has been shown that the levels of self-reported sadness did not vary as a function of the emotional valence of film clips in clinically depressed patients, whereas healthy individuals reported higher levels of sadness in sad rather than neutral and pleasant film clips. In addition to the subjective emotional experience, the ECI hypothesis has been tested using measures of emotion-expressive behavior (e.g., zygomatic or corrugator electromyography, EMG), the eyeblink startle reflex and psychophysiological reactivity. Consistent with the ECI hypothesis, patients with MDD are likely to be characterized by reduced facial EMG modulation during an affective imagery task compared to healthy controls (Gehricke and Shapiro, 2000 and Greden et al., 1986), although mixed results exist (Rottenberg, Gross, et al., 2005). Likewise, there is evidence of reduced affective modulation of the startle reflex during the passive viewing of affective pictures in clinically depressed patients (Allen et al., 1999, Dichter et al., 2004 and Kaviani et al., 2004) and nonclinical depressed individuals (Mneimne, McDermut, & Powers, 2008; but see also Sloan & Sandt, 2010) compared to healthy controls.

3.1. Self-report measures The mixed ANOVA on valence ratings yielded a significant main effect for Category, F(2,104) = 340.15, p < .001, ɛ = .98, ηp2 = .87. Fisher's LSD post hoc tests showed that the unpleasant scripts were evaluated as significantly more unpleasant than the neutral and the pleasant scripts (all ps < .001). In turn, the pleasant scripts were rated as significantly more pleasant than the neutral ones (p < .001). No significant main effect for Group or Group × Category interaction was found (all ps > .32). Similarly, the ANOVA on arousal ratings revealed a significant main effect for Category F(2,104) = 97.09, p < .001, ɛ = .99, ηp2 = .65. Specifically, arousal was great for both pleasant and unpleasant scripts compared to the neutral ones (all ps < .001), whereas no significant difference in arousal between the unpleasant and the pleasant scripts was noted (p = .94). No significant main effect for Group or Group × Category interaction was found (all ps > .05). With respect to the self-reported vividness of the imagery, no significant main effect or interactions were noted (all ps > .08). The descriptive statistics of each self-report measure are reported in Table 1. Table 1. Ratings of each self-report measure in the group with and without dysphoria. Self-report measure Group without dysphoria (N = 29) Group with dysphoria (N = 25) Pleasant Neutral Unpleasant Pleasant Neutral Unpleasant Valence 8.0 (1.0) 6.2 (1.0) 2.6 (0.9) 7.6 (1.3) 6.2 (1.1) 2.6 (1.0) Arousal 6.5 (1.6) 2.8 (1.2) 6.3 (1.6) 6.5 (1.6) 4.0 (1.6) 6.8 (1.3) Vividness 6.7 (1.4) 7.2 (1.1) 6.6 (1.3) 7.2 (1.6) 7.4 (1.3) 7.0 (1.4) Note. Data are M (SD). Table options 3.2. Cardiac autonomic reactivity 3.2.1. Heart rate The preliminary ANOVA on HF peak did not reveal a significant main effect or interactions involving Group (all ps > .14), thus excluding any potential interference of respiratory rate. The mixed ANOVA on heart rate yielded a significant Time main effect, F(1,52) = 12.51, p < .001, ηp2 = .19, and Time × Category, F(2,104) = 4.35, p < .03, ɛ = .89, ηp2 = .08, and Group × Time × Category F(2,104) = 3.33, p < .05, ɛ = .89, ηp2 = .06, interactions ( Fig. 1). Specifically, Fisher's post hoc tests revealed that heart rate significantly increased from baseline to the active imagery of pleasant (p < .001, Cohen's d = 0.20) and unpleasant (p < .003, Cohen's d = 0.20), but not neutral (p = .86, Cohen's d = 0.01), scripts in the group without dysphoria. By contrast, heart rate increased from baseline to the active imagery of unpleasant (p < .001, Cohen's d = 0.27) and neutral (p < .009, Cohen's d = 0.13), but not pleasant (p = .10, Cohen's d = 0.08), scripts in the group with dysphoria. Similarly, while no differences in baseline heart rate were noted within groups (all ps > .26), heart rate was greater during the pleasant than the neutral active imagery in individuals without dysphoria (p < .006, Cohen's d = 0.15), but not in those with dysphoria (p = .45, Cohen's d = 0.04). With respect to the unpleasant imagery, heart rate was significantly or marginally significantly increased during the unpleasant than the neutral active imagery in the group without dysphoria (p = .06, Cohen's d = 0.15) and with dysphoria (p < .04, Cohen's d = 0.10). Individuals with, but not those without, dysphoria showed increased heart rate during the imagery of the unpleasant than the pleasant scripts (p < .004, Cohen's d = 0.14). No differences between groups in baseline or active imagery were noted (all ps > .33). No other significant main effects or interactions were noted.