کنترل توجه رابطه بین عدم تحرک تونیک و خاطرات مزاحم را تحت تاثیر قرار می دهد

Abstract Background and objectives Cognitive control and tonic immobility (TI) have both been implicated in the development of PTSD, but it is not known how these factors are related. The present study investigated if a specific form of cognitive control (attentional control) would moderate the relationship between TI and intrusive memories. Methods Participants (N = 43) completed the Attentional Control Scale (ACS) before watching an aversive film. They completed the Tonic Immobility Scale (TIS, with an immobility and fear subscale: TIS-TI and TIS-Fear) afterwards and recorded intrusive memories of the film in the subsequent week. Results TIS-TI was related to intrusion frequency, while ACS was not. However, ACS had a moderating role; the relationship between TIS-TI and intrusion frequency was significant in low ACS but not in high ACS participants. The TIS-Fear subscale was not related to intrusion frequency in low ACS or high ACS participants. Limitations Replication of the results is merited in selected extreme groups and males. Conclusions The results may imply that enhanced attentional control serves as a protective factor against the development of intrusive memories after trauma.

Introduction Threat responses such as flight (avoidance) are intensely investigated and proved of great importance in the aetiology of threat-related psychopathology (e.g., posttraumatic stress disorder, PTSD), thereby providing useful treatment strategies (Brewin, 2006). However, threat responses typically include several stages: fight-flight is preceded by a freezing response and possibly followed by tonic immobility (TI; Lang et al., 1997 and Marx et al., 2008). TI has been described as the final stage after encountering a predator. When escape or resistance is unsuccessful, prey animals may enter in a death-feigning state of TI, which may be of evolutionary advantage in that many predators are interested in living prey only. The most pronounced features of TI are physical immobility and muscular rigidity, but additional features such as suppressed vocal behavior, analgesia, waxy flexibility and tremors in the extremities have also been reported (Gallup, 1974). However, in TI the prey animal is still highly alert and features of the event and the environment are still actively processed. Despite the numerous studies that have focused on human fight–flight responses, freezing and TI have been described in non-human animal studies mainly. The few studies that investigated the effects of peritraumatic TI in humans have shown its potential importance with respect to the development of psychological impairment and psychiatric disorders such as PTSD (Bovin et al., 2008, Galliano et al., 1993 and Heidt et al., 2005). There is also some prospective evidence for the role of TI in PTSD development. An experimental PTSD analogue study showed that (either voluntary or involuntary) immobility during an aversive film resulted in more intrusive memories of that film relative to free-to-move counterparts (Hagenaars, Van Minnen, Holmes, Brewin, & Hoogduin, 2008). Immobility also seemed to affect intrusion quality as it was associated with intrusive images, but not intrusive thoughts (Hagenaars, Brewin, Van Minnen, Holmes, & Hoogduin, 2010). However, it remains unclear to what extent induced immobility is similar to spontaneous immobility. The present study therefore used an observational, quasi-experimental design with an aversive film to model a traumatic experience. Theoretically, TI could enhance PTSD development in several ways. First, victims were more likely to be blamed if they did not show active struggling (McCaul, Veltum, Boyechko, & Crawford, 1990), which may result in less post-trauma social support and more negative cognitions about oneself, both predictive factors in PTSD development (Ehlers and Clark, 2000 and Ozer et al., 2003). Second, the intense peritraumatic distress associated with TI may be responsible for later PTSD development, possibly as an indicator of perceived life stress (Ozer et al., 2003) or trauma severity (Brewin, Andrews, & Valentine, 2000). Third, controllability is considered a key factor in TI as well as PTSD development (Marx et al., 2008). That is, physical restraint or entrapment and intense fear are the two conditions that elicit TI. Animals indeed showed increased susceptibility to TI after an uncontrollable than after an escapable shock (Maser & Gallup, 1974). So as a consequence, individuals with poor controllability capacities may be more vulnerable to experience TI. TI might also specifically affect the development of intrusive memories. That is, another defense response that includes immobility (freezing) is associated with enhanced sensory intake (Bradley, Codispoti, Cuthbert, & Lang, 2001). This may cause a dominantly perceptual information processing style, which is considered to result in the development of vivid, intrusive memories (Ehlers & Clark, 2000). Indeed, a previous experiment showed that immobility during an aversive film resulted in higher frequencies of intrusive memories of that film (Hagenaars et al., 2008). It has been suggested that cognitive control affects the development of involuntary memories. The fact that involuntary memories were found to be associated with self-reported weaker cognitive control (distractability; Verwoerd & Wessel, 2007), as well as with deficient inhibitory control that showed on experimental tasks (Verwoerd, Wessel & De Jong, 2009) seems to confirm this idea. Note that in the latter study, involuntary memories were associated with inhibition at the cognitive level and not response inhibition, suggesting the relevance of cognitive control. Additional evidence comes from studies on working memory capacity. For example, lower working memory capacity was associated with relatively high levels of intrusive memories (Klein & Boals, 2001), whereas people with high working memory capacity were better able to suppress intrusive thoughts (Brewin and Beaton, 2002 and Brewin and Smart, 2005). Working memory capacity refers to “the ability to control attention to maintain information in an active, quickly retrievable state” (Engle, 2002, p. 20). By definition, it is at least related to but possibly isomorphic to the concept of executive attention or attentional control. Moreover, self-reported low attentional control was also related to higher intrusive memory frequency in an experimental study, although this was true for the participants that had to record their intrusions in a diary and not for those who had to complete a questionnaire assessing intrusive memories only (Verwoerd, De Jong, & Wessel, 2008). The first aim of the present study concerns the associations between attentional control and TI, and intrusion development. It was hypothesized that poor attentional control and more TI would be associated with increased intrusion frequency. Second, following Derryberry and Reed (2002), attentional control was hypothesized to serve as a moderator. That is, although TI is thought to enhance the development of intrusive memories (Bovin et al., 2008 and Hagenaars et al., 2008), this effect may be neutralized in participants with high attentional control, as these participants would to be able to inhibit their intrusive memories (Verwoerd et al., 2009). Poor attentional control may be related to general psychological distress, or negative affect (e.g., Derryberry & Reed, 2002), which can affect memory and attention processes (e.g., concentration problems) and thus intrusion development. The present study therefore controlled for neuroticism.

3. Results The data were checked for outliers on all measures. One participant was an outlier on intrusive memories, scoring more than three times the interquartile range above the upper quartile. Her score was changed into a score that was one unit higher than the next most extreme score in the distribution, so that the between-subject order remained the same (Tabachnick & Fidell, 1996). The film caused large increases in horror from pre (M = .37, SD = .76) to post film (M = 5.58, SD = 2.26), suggesting it was adequate as a stressor (t(42) = −15.61, p < .0001). TIS-TI was related to intrusive memories (r = .34, p = .03), TIS-Fear was not (r = .12, p = .47). A partial correlation, controlling for EPQ-N yielded no association between ACS and intrusion frequency (r = .07, p = .66). An additional partial correlation was executed to check whether the association between TIS-TI and intrusive memories would remain significant after controlling for EPQ-N, which was indeed the case (r = .37, p = .02). Finally, ACS was not related to TIS-TI (r = −.21, p = .18) or TIS-Fear (r = −.10, p = .55). The ACS not being related to the predictor (TIS) and the criterion (intrusive memories), provides optimal conditions for interpretations as a moderator ( Baron & Kenny, 1986). Next, it was examined whether ACS would indeed moderate the TIS – intrusive memories relationship. Linear regression analyses with main (ACS, TIS-TI and TIS-fear) and interaction terms (ACS × TIS-TI and ACS × TIS-Fear) as predictors and intrusive memories as dependent variable were not applicable because of multicollinearity between the predictors (Tolerance < .04 and VIF > 35 for all predictors). Therefore, following Derryberry and Reed (2002), the sample was divided in half by a median split on the ACS in order to investigate whether the TIS – intrusive memories relationship would be different for high versus low ACS participants. This resulted in 22 low ACS and 20 high ACS participants (see Table 1 for means and SDs). High and low ACS participants did not differ on EPQ-N (t(40) = .94, p = .35). One participant had a median score and was therefore not selected for the high or low ACS group ( Fig. 1). Correlations between TIS-TI and intrusive memories and TIS-Fear and intrusive memories were not significant in the high ACS group (r = .14, p = .59 and r = .06, p = .83 respectively). However, the correlation between TIS-TI and intrusive memories was significant in the low ACS group (r = .48, p = .02), whereas the correlation between TIS-Fear and intrusive memories was not (r = .22, p = .33). Visual inspection of the scatter plot confirmed that the TIS-TI – intrusive memory correlation in the low ACS group was not based on a few extreme, influential data points. 1 Table 1. Mean scores (SDs) on attentional control, tonic immobility and intrusion frequency (N = 43). ACS TIS-Fear TIS-TI Intrusions Total sample 52.51 (9.12) 6.84 (3.89) 11.72 (5.87) 3.07 (3.74) Low ACS (n = 22) 45.45 (6.06) 6.73 (3.34) 13.64 (4.92) 2.89 (3.33) High ACS (n = 20) 60.25 (4.73) 7.25 (4.28) 9.95 (6.27) 3.23 (4.21) Note. ACS = Attentional Control Scale; TIS-Fear = Tonic Immobility Scale-Fear subscale; TIS-TI = Tonic Immobility Scale-Immobility subscale. Table options The overall moderation model based on the current data: attentional control ... Fig. 1. The overall moderation model based on the current data: attentional control moderates the relationship between tonic immobility and intrusive images.