واکنش پذیری عاطفی و نیروی کنترل: تاثیر بازداری رفتاری

Abstract Individual difference measures have been shown to alter emotional arousal and emotional arousal alters force production during force control tasks. In the current study we examined whether individual differences in behavioral inhibition influence force control during emotional image viewing. Subjects who scored high and low in behavioral inhibition (BIS) produced force with visual feedback for 5 s. Feedback was then removed and replaced by a mutilation, attack, erotica, or neutral image for 6 s. The magnitude and direction of error in force production during image presentation was compared between groups and across image type. The high BIS group displayed a relative increase in force production during exposure to attack and mutilation images compared to the low BIS group. Bias scores (i.e., comparison of unpleasant image to neutral or pleasant image) further confirmed these findings by demonstrating a relative increase in force for the high BIS group during attack and mutilation images as compared to erotica images, whereas the low BIS group displayed the reverse effect. Together these findings extend the premise of action readiness to demonstrate that dispositional differences in behavioral inhibition interact with emotional state to alter force production.

Introduction One subcomponent of emotional expression is action readiness (Frijda, 1986 and Frijda, 2009). Emotion driven changes in action readiness have been demonstrated across a range of tasks using a range of different experimental approaches. Behavioral and neurophysiological studies have shown that viewing emotional stimuli leads to changes in excitability of the corticospinal motor tract (Coombes et al., 2009 and Hajcak et al., 2007), the initiation and execution of approach and avoidance arm movements (Chen and Bargh, 1999 and Rotteveel and Phaf, 2004), the amplitude, accuracy, and variability of force control (Coombes et al., 2006, Coombes et al., 2007a, Coombes et al., 2007b, Coombes et al., 2008 and Coombes et al., 2005), and changes in posture and the initiation of gait (Hillman, Rosengren, & Smith, 2004: Naugle, Joyner, Coombes, Hass, & Janelle, accepted for publication). Related work has demonstrated links between subclinical depression and a reduction in force amplitude following transcranial magnetic stimulation (Oathes & Ray, 2006), and clinical bipolar depression and the steadiness and velocity scaling of force production (Lohr & Caligiuri, 2006). The DSM-IV diagnostic criteria for major depression include agitation and psychomotor retardation which present clinically as a reduction in speed, a delay in motor initiation, body immobility, and postural abnormalities. Rates of agitation and psychomotor retardation in depressed individuals ranges from 46% to 67% (Sobin & Sackeim, 1997). In addition to the co-morbid motor abnormalities in depression, atypical balance and motor functions have been reported among individuals with high trait anxiety (Coombes et al., 2009 and Wada et al., 2001), phobic/panic symptoms (Yardley, Britton, & Lear, 1995), and obsessive compulsive disorder (Leocani, Locatelli, & Bellodi, 2001). While it is clear that individual differences and experimentally induced emotional states independently influence the motor system, it is not fully understood how these factors interact to influence voluntary motor control. All previous work which has integrated emotion and motor control has either implemented a between group design to examine force control in depression (Lohr and Caligiuri, 2006 and Oathes and Ray, 2006), or has used a within-subject design to examine how experimentally induced emotional states alter motor system activity (Chen and Bargh, 1999, Coombes et al., 2008 and Hajcak et al., 2007). The objective of the current paper was to examine how behavioral inhibition interacts with emotional state to influence one’s ability to control force production. 1.1. Behavioral inhibition system (BIS) Reinforcement Sensitivity Theory (RST) postulates the existence of three major systems of emotional responding: the behavioral inhibition system (BIS), the behavioral activation system (BAS), and the fight/flight/freeze system (FFFS) (Gray, 1970 and Gray, 1982; Gray & McNaughton, 2000). BIS is hypothesized to regulate affect and behavior in response to signals of punishment, non-reward, and novel stimuli, whereas BAS directs behavior in response to appetitive and rewarding cues. Individuals high in BIS sensitivity are characterized by worry proneness and anxious rumination, which ultimately lead to a constant vigilance for danger and a high susceptibility for anxiety disorders (Corr & McNaughton, 2008). Founded on Gray’s BIS and BAS framework, Carver and White (1994) developed the first valid and reliable self-report measures (BIS/BAS scales) of sensitivity to BIS and BAS activation. The BIS and BAS scales primarily focus on affective consequences (i.e., how a subject would feel in response to various situations), and have consistently supported the existence of Gray’s two orthogonal systems (e.g., Gomez & Gomez, 2002). Given that the BIS scale has been robustly implicated in affective disorders the focus of the current study was on behavioral inhibition. Greater relative BIS activation coincides with exposure to conditioned and unconditioned aversive stimuli, leading to increased negative valence of the aversive stimuli as well as heightened arousal and attention, anxiety, passive avoidance, and the inhibition of behavior that may result in painful or negative consequences (Gray, 1994). Comparatively higher scores on the BIS scale have been associated with negative affect and self-reported anxiety (Buickians et al., 2007 and Segarra et al., 2007) and the processing of unpleasant information such as during exposure to blood and disgust images (Caseras et al., 2006 and Gomez and Gomez, 2002). BIS activation also correlates with greater right posterior temporal and parietal cortical activity (Hewig, Hagemann, Seifert, Naumann, & Bartussek, 2006) and these cortical regions have been linked to greater anxious arousal (Nitschke, Heller, Palmieri, & Miller, 1999). Hence, evidence suggests that unpleasant cues elicit more intense emotional responses in individuals who show relative increases in BIS sensitivity. 1.2. BIS: implications for emotion and movement Unpleasant emotional states prime movements away from the body, whereas pleasant emotional states prime movements towards the body (Chen & Bargh, 1999). However, evidence also suggests that emotional arousal rather than emotional valence alters gripping tasks that do not require movements that are directed towards or away from the body (Coombes et al., 2008 and Schmidt et al., 2009). For instance, in the Coombes et al. study participants produced a pinch-grip force to a visible target line. Feedback was removed after 5 s and replaced with a pleasant, unpleasant, or neutral image. Although a decrease in force production was demonstrated (Vaillancourt & Russell, 2002), the magnitude of the decrease was greatest for neutral images as compared to pleasant and unpleasant images. The authors concluded that emotional arousal leads to a relative increase in force production. This emotional arousal effect was recently replicated and extended to a power grip task by Schmidt and colleagues who showed that the amplitude of maximal force production was increased following the presentation of pleasant and unpleasant as compared to neutral images. Although individual differences in affective disposition reliably predict the degree of emotional reactivity to affective stimuli, important questions remain concerning how individual differences and emotional state interact to influence a hand gripping task which is a critical component of many acts of daily living including drinking, eating, driving, and grooming. In the current study a high BIS group and a low BIS group completed a precision grip force control task during exposure to pleasant, unpleasant, and neutral images. Given the wealth of evidence that has emerged concerning the neurobiological foundations and behavioral manifestations of BIS, we expected individuals with greater BIS sensitivity to experience more intense emotional responses (i.e., greater arousal) to unpleasant images which would be reflected behaviorally as a relative increase in force production during exposure to the unpleasant as compared to the pleasant and neutral images.

Results 3.1. Constant error The Student t test indicated that CE during the 1 s interval immediately preceding image onset did not vary as a function of BIS group, t(35) = 1.66, p > .05. Consequently, any changes in CE during image onset were not a function of group differences in force production prior to image onset. The two-way ANOVA on the final 1 s of image presentation revealed a significant main effect of group, F(1, 35) = 4.76, p = .036, indicating that the high BIS group displayed a relative increase in force production as compared to the low BIS group. A significant main effect of valence was also evidenced, F(2.56, 89.68) = 123.979, p < .05, revealing a relative decrease in force production during all image presentation trials as compared to control trials. Each main effect was qualified by a significant Group × Valence interaction, F(2.56, 89.63) = 3.179, p < .05, with follow-up tests revealing that the High BIS group demonstrated a relative increase in force production during the presentation of attack and mutilation images as compared to the Low BIS group during the presentation of attack, mutilation, and neutral images. Finally, in line with the main effect of valence, follow up tests revealed that both groups demonstrated a relative decrease in force production during all image presentation trials as compared to control trials. 3.2. Mean force The Student t test indicated that mean force during the 1 s interval immediately preceding image onset did not vary as a function of BIS group, t(35) = 1.71, p > .05. Consequently, any changes in force production during image onset were not a function of group differences prior to image onset. Fig. 2 shows mean force amplitude during the final epoch of each trial for the low BIS group (black bars) and the high BIS group (grey bars). Both groups produced approximately 35% of MVC during the control condition. The figure also shows that the high BIS group displayed a relative increase in force production during attack and mutilation images as compared to the low BIS group. The two-way ANOVA on the final 1 s of image presentation demonstrated a significant main effect of valence, F(4, 140) = 151.6, p < .001, revealing greater force production during the control condition compared to all image conditions. The main effect was superseded by a significant Group × Valence interaction, F(4, 140) = 3.39, p = .017. Follow-up tests revealed that the High BIS group demonstrated greater force production during the presentation of (1) attack images compared to the Low BIS group during the presentation of attack and neutral images, and (2) mutilation images compared to the Low BIS group during exposure to mutilation, attack, and neutral images. Additionally, both groups produced more force during the control condition compared to all other conditions. The main effect of group was not significant, F(1, 35) = 2.90, p = .098. Normalized mean force scores across valence conditions. The black bars represent ... Fig. 2. Normalized mean force scores across valence conditions. The black bars represent the normalized mean force scores for the low BIS group and the grey bars represent the normalized mean force scores for the high BIS group. The target force was 35% of MVC. Error bars represent ±1 SE. Figure options Fig. 3 shows the planned comparisons of the mean bias scores for the low BIS group (black bars) and the high BIS group (grey bars). A significant effect of group was demonstrated on bias scores which contrasted force production during attack and erotica images, t(35) = −2.36, p = .024 (see A-E in Fig. 3). The High BIS group showed a relative increase in force production during exposure to attack as compared to erotica images, whereas the Low BIS group displayed a relative increase in force production during exposure to erotica as compared to attack images. A significant effect of group was also found for the mutilation-erotica bias score, with the data following the same pattern as the attack-erotica bias score, t(35) = −2.45, p = .031 (see M-E in Fig. 3). The mean force bias scores for mutilation-neutral (t(35) = −0.503, p > .05) and attack-neutral (t(35) = −1.056, p > .05) conditions were not significantly different. Normalized mean force bias scores for the low BIS group (black bars) and the ... Fig. 3. Normalized mean force bias scores for the low BIS group (black bars) and the high BIS group (grey bars) for each bias score. The High BIS group displayed increased force production during exposure to attack and mutilation images as compared to erotic images. The Low BIS group displayed greater force production during exposure to erotica as compared to attack and mutilation images. Error bars represent ±1 SE. ∗ = p < .05. M = mutilation, A = attack, E = erotica, N = neutral.