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Introducing the Trier Social Stress Test in a new experimental paradigm enabling complex emotional learning and unlearning
Abstract
The present study had two main aims. Firstly, to introduce a paradigm to the field of emotional learning and unlearning that is of high external and ecological validity. The Trier Social Stress Test (TSST), widely utilised for stress induction in psychological research, was used as a means of acquiring autobiographical negative event memory that can be retrieved and manipulated, to make investigation of different interventions possible. Secondly, to compare effects of imagery rescripting therapy (ImRs) and imaginal exposure (IE), two imagery interventions hypothesised to have different working mechanisms, on emotional responses and physiological activity related to the negative event memory. Results indicated that, in a three-day set-up, the TSST could be used to reliably elicit physiological and subjective emotional responses on the first day of testing. Twenty-four hours later, these responses could be reliably reactivated, and were subsequently manipulated through imagery interventions (i.e., ImRs or IE). Finally, the negative event memory of the TSST could be reactivated on the third day of testing, but no differences between the two imagery interventions could be observed. It can be concluded that the TSST paradigm offers an alternative of higher external and ecological validity than currently popular paradigms, such as fear conditioning using pictures and electric shocks or traumatic film clips, because the emotional memory is of autobiographical nature and the complexity of the emotional experience heightens ecological validity of fear learning in an experimental setting. Although in the present study, no differences in the effects of ImRs and IE could be found, participants rated ImRs as more pleasant and distress decreased more during ImRs than during IE. More research is needed to unveil the elements of ImRs responsible for its effects.
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1. Introduction
In previous fear learning research associative learning models (i.e., fear conditioning paradigms) presented a widely used and valuable tool providing insight into the formation, consolidation and expression of fear memories and their (neuro) biological underpinnings (e.g., Beckers, Krypotos, Boddez, Effting, & Kindt, 2013; Craske, Hermans & Vansteenwegen, 2006). While these paradigms have taught us a great deal about learning and unlearning in anxiety disorders (Mineke & Zinbarg, 2006), they do however pose several problems. First, their external and ecological validity is relatively low: The relatively simple CS-UCS association created by the pairing of for example electric shocks (the unconditioned stimuli; UCS) to pictures (the conditioned stimuli; CS) are not sufficiently representative of the fear memories involved in anxiety disorders, such as post-traumatic stress disorders (PTSD), where fear memories are the result of far more complex fear networks and associations (Foa & Kozak, 1986; Foa, Steketee, & Rothbaum, 1989). Second, these simpler
paradigms are not suited to investigate the mechanisms underlying therapeutic techniques other than exposure (e.g., imagery rescripting or EMDR); rescripting or desensitizing the pairing of shocks to pictures is not of external relevance to the investigation of the much more complex memory in anxiety disorders.
The present study aims at introducing a new paradigm that tackles these problems, by creating a negative event memory that is more complex because the event is of autobiographical nature and of personal relevance to a participant, heightening the external and ecological validity of the paradigm. For this purpose, the Trier Social Stress Test (TSST; Kirschbaum, Pirke & Hellhammer, 1993) was used as a negative emotional experience. The TSST is widely used for stress induction in
psychological research (Dickerson & Kemeny, 2004) and consists of a laboratory procedure in which participants perform a set of tasks before a stern evaluative panel. Since participants reliably respond to the TSST with strong physiological and subjective stress responses (Kirschbaum, Pirke &
Hellhammer, 1993; Birkett, 2011), we expected the TSST to be a suitable instrument in the study of emotional memory, creating relevant autobiographical negative event memory. Importantly, the TSST does not only present us with more relevant negative event memories, but it also offers a way to
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investigate the working mechanisms of therapeutic interventions, by retrieving, manipulating and subsequently testing the TSST memory. This is particularly relevant as traditional associative learning paradigms are not well suited for this purpose. Given the contingency-based nature of the fear
memories formed by these models (i.e., CS-UCS association), fear conditioning paradigms do not seem to lend themselves for the investigation of therapeutic techniques attempting to change the meaning of a stimulus independently of any experience explicitly aimed at affecting the CS-UCS association. Imagery rescripting therapy is such a technique. In ImRs, the course of events of aversive experiences in memory is changed through imagery exercises, where the meaning of the cognitive representation of the original aversive event is changed by gathering additional information about it (Arntz, 2012). Patients are asked to activate the negative event memory and then mentally rescript what happened into less emotionally disturbing images. For example, a traumatic memory of a violent robbery is rescripted by a patient imagining the police arrive and prevent the crime (Dibbets, Poort & Arntz, 2012). This process of actively changing the memory is called UCS-revaluation and is
hypothesised to be more prominent in ImRs than in exposure. Contrary to extinction following exposure, UCS-revaluation generalises to other stimuli and contexts, since not the specific CS-UCS associations, but the UCS-representation itself is directly targeted. This could result in less relapse compared to extinction-based therapies, in which fear responses often return outside the extinction context (Bouton, 2002), offering a major advantage of ImRs (Arntz, 2012; Dibbets, Poort & Arntz, 2012; Davey, 1989). Thus, if ImRs indeed works through UCS-revaluation, as is hypothesised, it might serve as a useful alternative to exposure therapy in the treatment of anxiety disorders and PTSD (for a review see Arntz, 2012). Specific knowledge of and experimental research into the underlying mechanisms of ImRs is lacking, and research is needed to optimise the effectiveness of the therapy. More traditional fear learning paradigms do not lend themselves well to investigate this. To enable rescripting, aversive stimuli need to possess characteristics that a participant can actively modify by changing or adding (fictional) details during the ImRs intervention. Therefore, new experimental paradigms are needed that evoke fear memories complex and multifaceted enough to lend themselves for the investigation of rescripting techniques. Important steps have been taken towards this goal, introducing complex and meaningful film stimuli within the traditional fear conditioning paradigm
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(Kunze, Arntz, & Kindt, submitted manuscript; Leer et al., 2013), but there is still room for
improvement. Fear memory generated by film fragments is not of autobiographical nature, as it is in the pathogenesis of anxiety disorders. A new experimental paradigm, in which fear memory is acquired that is both complex and autobiographical, would enable the investigation of the working mechanisms of ImRs in an experimental setting of higher external and ecological validity.
Thus, the goal of the present study was twofold: Firstly, we set out to test the TSST as a means of acquiring a complex memory of an aversive event. Secondly, we aimed to study the underlying process of ImRs by comparing this intervention to extinction-based imaginal exposure therapy. To address these research questions, participants were subjected to a three-day procedure. On the first day, participants underwent a stressful task presenting in front of a stern panel (i.e., the TSST). Based on previous results (e.g., Birkett, 2011), a response to the TSST on physiological (heightened heart rate and skin conductance levels) and self-report measures (distress ratings and several mood
questionnaires) was expected. On the second day, reactivation of the acquired negative event memory took place. A return of the physiological and emotional responses, necessary in order to manipulate the memory and attempt to affect responses with the imagery interventions. This was expected based on pilot testing using the TSST as well as research into fear conditioning using aversive film stimuli in a two-day paradigm in our lab (Bos & Kindt, unpublished; Kunze, Arntz & Kindt, submitted manuscript), where return of negative emotion was found. To reactivate the negative event memory, participants were instructed to close their eyes and actively recall what happened on the first day of testing. On the third day, the effects of the interventions on negative event memory were tested: participants were told to perform tasks again, and the return of negative emotion was measured. Return of fear is often used as an analogue to relapse, and is a reliable measure used in experimental settings (Dibbets, Poort & Arntz, 2012). If ImRs works through UCS-revaluation, rather than exposure, it is expected that less return of negative emotion after reactivation of the aversive TSST memory should be observed in the ImRs condition, compared to the exposure condition.
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2. Method
2.1 Participants
Sixty-three healthy female1 undergraduate students from the University of Amsterdam participated in this study, approved by the Ethics Committee of the university. The participants were screened for current mental and/or physical illness and prescribed medication or drug intake during participation before providing written informed consent. Participants were compensated with partial course credit or a monetary reward (25 euro). Following the screening procedure, participants were randomly allocated to either the imagery rescripting (N=29) or the imaginal exposure (N=30) condition.
2.2 Materials
2.2.1. Trier Social Stress Test
An adaptation of the Trier Social Stress Test (TSST; Kirschbaum, Pirke & Hellhammer, 1993) was used to mimic a real-life negative experience. The task consisted of a presentation about participants’ own positive and negative character traits, a mathematical exercise (counting backwards in steps of 13, starting at 1310) and singing a well-known Dutch children’s song (“Poesje Mauw”). The lyrics of the song were available for participants who did not know the words. The three tasks were performed seated in front of a stern evaluative jury (1 male, 1 female; Duchesne, Tessera, Dedovic, Engert & Pruessner, 2012) trained for this purpose and a video camera2.
2.2.2. Imagery intervention
The procedure of the interventions was adapted from Hagenaars & Arntz (2012). Following 5 minutes of instructions and guided imaginal reactivation of the memory by the experimenter, all participants were instructed to picture what happened during the task on day I. In line with standard imaginal exposure treatment protocol, participants were asked to talk in the first person and the present tense, to increase vividness and involvement (Dancu & Foa, 1993). Vividness was rated after guided reactivation on a scale from 0 (“not at all vivid”) to 10 (“extremely vivid”). The experimenter facilitated the process where needed by reminding the participant to stick to the present tense and the
1 The number of females willing to participate in the experiment far exceeded the number of males. To aid interpretations and keep distributions across conditions equal, no males were included.
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first person. Before and after the intervention, participants indicated their distress using Subjective Units of Distress (SUDs) on a scale of 0 (“not at all distressed”) to 10 (“extremely distressed”). All interventions lasted about 9 minutes (ImRs: M=8.6 min, SD=1.5 min; IE: M= 10.5 min, SD = 2.2 min), from the start of the guided reactivation to the post-intervention rating of distress. Duration of the imaginal exposure interventions were matched to the duration of the imagery rescripting
interventions during pilot testing. 2.2.2.1 Imagery rescripting
After reactivation, participants were asked to change the most distressing part of the memory by imagining and verbalising a more preferable course of events, resulting in a more satisfying outcome for the participant. Participants were allowed to change the course of events into anything they liked, realistically possible (e.g., by refusing to perform the task) or not (e.g., by introducing Superman). 2.2.2.2 Imaginal exposure
After reactivation, participants were instructed to repeatedly re-experience the most distressing part of the TSST by imagining and verbalising what happened, as if they were experiencing it in the here and now, focussing on sensory details (what they see, hear, smell, feel, etc.) and their emotions.
Participants were not allowed to change the course of events in any way.
2.3 Measures
2.3.1. Physiological measures 2.3.1.1. Heart rate
Heart rate was measured using a custom built input device with a sine curve shaped excitation voltage (IV, pk-pk, 50 Hz). Three 3M Red Dot electrodes were placed just below the left and right clavicles and 5 cm above of and 2 cm to the left of the umbilicus. The signal was amplified and digitised at 1000 Hz by a 16-bit AD-converter (National Instruments, NI-USB6210). An integrated peak-detector identified R-waves and amplified them into TTL pulses. Raw ECG scores were transformed to normalise the distributions. ECG data was analysed using the Vsrrp98 software by extracting the peak value (i.e., inter-beat interval) within every 5 seconds of recording.
7 2.4.1.2. Electro dermal activity
Skin conductance levels were measured using a custom built input device with a sine curve shaped excitation voltage (1V pk-pk, 50 Hz). Two Ag/AgCl electrodes (20x16mm) were placed on the medial phalanges of the ring and index finger of the non-preferred hand. The incoming signal was amplified and digitised at 1000 Hz using a 16-bit AD-converter (National Instruments, NI-USB6210). Raw SCL scores were transformed to normalise the distributions. SCL data was analysed using the Vsrrp98 software by extracting the peak SCL value within every 5 seconds of recording.
2.3.2. Subjective measures 2.3.2.1. Questionnaires
Anxiety levels (STAI-S and STAI-T) were assessed by the State-Trait Anxiety Inventory
(Spielberger, Gorsuch, Lushene, Vagg, & Jacobs, 1983). Mood changes in response to the TSST and reactivation of the memory of the TSST were measured by the Positive and Negative Affect Schedule (PANAS; Watson, Clark, & Tellegen, 1988; Crawford & Henry, 2004). The STAI-S and PANAS were administered twice daily, at pre- and post-assessment.
2.3.2.2. Mood and distress ratings
Participants indicated how ashamed, tense, anxious, angry and in control they felt on a continuous scale from 0 (“not at all”) to 100 (“extremely”), on visual analogue scales (VASs). The mood ratings were administered twice daily, at pre- and post-assessment. Participants also indicated how distressed they felt (i.e., Subjective Units of Distress, SUDs) on a scale from 0 (“not at all”) to 100
(“extremely”) at the beginning of day I, day II and day III, and before and after the intervention on day II.
2.4. Experimental procedure
The experiment consisted of three sessions on three consecutive days (60, 60 and 30 min respectively), separated by 24 hours (see Figure 1. for a schematic overview of the study).
Day I. After participants were screened for exclusion criteria and written informed consent was obtained, participants were randomly allocated to one of the two conditions: imaginal exposure (IE) or imagery rescripting (ImRs). After the first baseline tension measurement (SUDs, 0-100) and the
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screening phase, participants completed the STAI-T. Electrodes were then attached and the
participants were instructed to move as little as possible during the entire experiment. After the first mood ratings (PANAS1, STAI-S1, VASs1), a five minute neutral film clip (Coral See Dreaming,
Hannan, 1999) was shown while taking baseline measurement of heart rate and electro dermal activity. Participants then received instructions on the TSST. A three minute preparation and anticipation period followed, in which participants were allowed to write down what they would say during the presentation. Before the jury was called in, their notes were taken away by the
experimenter, and the TSST started. Immediately after completing the TSST, participants filled in the mood ratings again (PANAS2, STAI-S2, VASs2). The TSST was performed sitting down, to reduce
disturbances in physiological measurement (Thayer, Ahs, Frederikson, Sollers & Wager, 2012). Day II. After attachment of the electrodes, participants answered questions about how well-rested they were, whether they had consumed drugs, alcohol, caffeine or nicotine in the past 12 hours, and rated their baseline tension (SUDs, 0-100) and mood (PANAS3, STAI-S3, VASs3). The 5-min
film clip was shown again while taking baseline heart rate and electro dermal measurements. Following the baseline measurements, the imagery interventions (i.e., IE or ImRs) took place. After the intervention, participants rated their moods again (PANAS4, STAI-S4, VASs4).
Day III. Again, electrodes were attached and participants answered the questions about how well-rested they were, whether they had consumed drugs, alcohol, caffeine or nicotine in the past 12 hours, and rated their baseline tension (SUDs, 0-100) and mood (PANAS5, STAI-S5, VASs5). The
five minute film clip was shown again while taking baseline heart rate and electro dermal measurements. Next, participants received the instruction that they would again be performing a couple of tasks in front of a different jury. A one minute anticipatory period followed, while the experimenter left the room to collect the panel, and the participant was left to wait. Then, participants rated their moods again (PANAS6, STAI-S6, VASs6), before being told they would not have to
perform any more tasks. Participants were then asked to fill in a short post-experimental
questionnaire, containing two questions: “Imagine, I would ask you to return tomorrow to perform the tasks of day I again. What are the chances you would do so (0-100)?”3, and “Imagine, you would
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indeed have to do the tasks of day I again. How much would you dread this (0-100)?”4.
Because imagery rescripting has previously been found to reduce intrusions of traumatic events (i.e., an aversive film fragment; Hagenaars & Arntz, 2012), a follow-up questionnaire was sent to the participants of the present study, investigating whether intrusions of the TSST are experienced and whether the amount or valence of intrusion differs between conditions. Data collection is still in progress and results will be available at a later stage.
Figure 1. Schematic overview of the experiment.
Day I. Approx. 60 min Day II. Approx. 60 min. Day III. Approx. 30 min.
Trait Anxiety & Mood Rating Mood Rating Mood Rating
Film clip Film Clip Film Clip
TSST Intervention Reactivation: Test
Mood Rating Mood Rating Mood Rating
2.5. Data reduction
Four participants were excluded from analysis because they did not return for the second day of the experiment, either for personal reasons (n=1) or due to the negative experience of the TSST (n=3). The final sample consisted of 59 participants with a mean age of 20.7 years (SD =1.98).
2.6. Data analysis
Physiological data were recorded continuously throughout the three days of the study. To aid selection of the relevant parts for analysis, markers were set manually by the experimenter at the start and end of the different phases of the study (before and after baseline, TSST, reactivation, intervention and
opnieuw te doen. Hoe groot is de kans dat u dat zou doen?” 4
“Stelt u zich voor, u moet de taken van dag 1 inderdaad opnieuw doen. Hoe erg zou u daar tegenop zien?”
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test, respectively). The maximum ECG and SCL values within each block were identified, to ensure no reactions would be nullified by averaging over blocks. Subsequently, ECG and SCL data were standardised into z-scores in order to normalise the distribution and to reduce between-subjects variability.
The main analysis entailed a series of mixed factorial repeated measures ANOVAs, using within-subjects factor Time (i.e. baseline vs. task, reactivation, and test respectively over all three days) and between-subjects factor Condition (ImRs vs. IE). A set of univariate ANOVAs with between-subjects factor Condition (IE vs. ImRs) were conducted on STAI-T, age, VASs and physiological data to assess between-group differences. For all ANOVAs, the Greenhouse-Geisser correction was used when sphericity assumptions were violated. A significance criterion was set at p< .05 for all analyses. The partial eta squared (p
2
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3. Results
3.1 Randomisation check
After randomisation, the two conditions did not differ in age, F(1,57)=.18, p=.675, p 2
<.01, or trait anxiety, F(1,57)=.67, p=.418, p
2
=.01. The two conditions also did not differ in negative affect, F(1,57)=3.11, p=.083, p 2 =.05, positive affect, F(1,57)=2.83, p=.098, p 2 =.05, reported anxiety, F(1,57)=.19, p=.669, p 2 <.01, tension, F(1,57)=.17, p=.682, p 2 <.01, anger, F(1,57)=2.19, p=.144, p 2 =.04, or control, F(1,57)=2.18, p=.145, p 2
=.04, at baseline. Participants in the ImRs group, however, reported significantly more shame at baseline on day I than their IE counterparts, F(1,57)=4.54, p=.037, p
2
=.74. Since our main interests are the effects of the interventions of day II, this difference is not regarded as relevant, especially given the fact that this difference between the groups was not observed at the beginning of day II, F(1,59)=.99, p=.324, p
2
=.017.
3.2 Testing the TSST-paradigm and comparing interventions 3.2.1. Day I. TSST: Stress induction
A series of mixed factorial repeated measures ANOVAs, with Time (pre vs. post TSST) as within subjects factor and Condition (ImRs vs. IE) as between subjects factor, was used to investigate the effect of the TSST on the various measures. The analyses showed significant increases during the TSST on state anxiety, Time: F(1,54)=79.49, p<.001, p
2 =.60, negative affect, F(1,48)= 41.66, p<.001, p 2 =.47, shame, F(1,57)=96.31, p<.001, p 2 =.63, anger, F(1,57)=25.56, p<.001, p 2 =.31, tension, F(1,57)=33.04, p<.001, p 2
=.37, and a negative effect on feeling in control, F(1,57)=44.85, p<.001, p2=.44. The TSST did not have a significant effect on fear, F(1,56)=.12, p=.728, p2<.01.
Physiological measurements also showed the TSST significantly enhanced SCL values, Time: F(1,56)=463.19, p<.001, p
2
=.89, and ECG values, F(1,54)=779.33, p<.001, p 2
=.94.
To ensure participants undergoing both interventions had had similar experiences regarding the TSST, changes from baseline 1 to TSST were compared across conditions. There was no significant difference between conditions for the VAS ratings on shame, F(1,57)=2.63, p=.11, p
2 =.04, tension, F(1,57)=1.07, p=.3, p 2 =.02 or control, F(1,57)=1.28, p=.26, p 2 =.02, on the STAI-S, F(1,54)=3.78,
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p=.057, p2=.07, on positive affect, F(1,53)=1.63, p=.21, p2=.03, or on negative affect, F(1,48)=2.95, p=.09, p
2
=.06. Regarding the physiological measures, there was no significant differences in SCL increase during TSST, F(1,56)<.01, p= .954, ηp
2
<.01 nor in ECG increase during TSST between conditions, F(1,57)=2.63, p=.11, p
2
=.04. ImRs participants were significantly more angry than their IE counterparts, F(1,57)=5.48, p=.023, ηp2=.09, but this difference had disappeared at the beginning
of day II, F(1,59)=.12, p=.73, ηp 2
<.01. See Figure 3 and 4 (p. 15) for ECG and SCL values for baseline vs. stress task, intervention and test respectively.
3.2.2. Day II. Reactivation 1:Intervention
A mixed factorial repeated measures ANOVA with within subjects factor Time and between subjects factor Condition showed a significant increase in reported feelings of anxiety from baseline on day II to after the guided reactivation in both conditions, Time: F(1.53)= 6.58, p=.013, p2=.11, and no
difference between the conditions could be observed, Time X Condition: F(1,53)=2.12, p=.152, p 2
= .04. There was a significant effect of Time, showing an increase in both ECG, F(1,54)=18.56, p<.001, p
2
=.26 and SCL, F(1,56)=77.77, p<.001, p 2
=.58, from baseline 2 to guided reactivation, indicating that the negative event memory for the TSST could successfully be reactivated. There was no
significant difference between the effect of time in the two conditions, for ECG, F(1,54)=.28, p=.602, p
2
=.03, or SCL, F(1,56)<.01, p=.964, p 2
<.01. After the intervention, participants evaluated the ImRs intervention as significantly more pleasant, F(1,57)=18.06, p<.001, and more agreeable,
F(1,57)=15.95, p<.001, than the IE intervention. There was no significant difference between the ratings of dreariness, F(1,57)=2.16, p=.147, and intensiveness, F(1,57)=.38, p=.539, between the two conditions. See Tabel 2 for descriptives.
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Table 2. Participant evaluation of interventions.
M (SD) ImRs IE Pleasant (‘plezierig’)** 44.37 (20.2) 65.36 (17.1) Dreary (‘naar’) 30.17 (24.1) 21.75 (19.1) Intense (‘intens’) 44.90 (22.1) 41.43 (20.6) Agreeable (‘aangenaam’)** 42.30 (20.9) 62.93 (18.3) ** p<.001.
There was a significant interaction effect between conditions during the intervention phase: From the start of the intervention after reactivation to the end of the intervention, participants in ImRs showed a decrease in SUDs, while participants in the IE condition showed an increase in SUDs, F(1,57)=60.59, p<.001, p
2
=.52 (see Figure 2).
Figure 2. Subjective units of distress pre and post intervention.
A repeated measures ANOVA (baseline day II vs. after intervention) showed that negative affect significantly decreased after the intervention in both conditions, Time: F(1,54)=9.34, p=.003, p
2
=.15. Positive affect increased, but not significantly, Time: F(1,54)=1.01, p=.319, p
2 =.02. There was no 0 10 20 30 40 50 60 70 Pre Post IE IMRS
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significant difference in decrease of negative affect or increase of positive affect across conditions, F(1,54)≤.3, p≥.589. State anxiety significantly decreased in both conditions, Time: F(1,56)=7.01, p=.01, p
2
=.11, while this effect also did not differ between conditions, Time X Condition: F(1,56)=.14 p=.71, p
2
<.01. After the intervention, anger decreased from baseline in both conditions, although this decrease was only marginally significant, Time: F(1,57)=3.81, p=.056, p
2
=.06, and did not differ between conditions, F(1,57)=.09, p=.765, p
2
<.01. There was a significant decrease in fear, Time: F(1,57)=7.15, p=.01, p
2
=.11, which did not differ between conditions either, F(1,57)=.43, p=.514, p
2
=.01. Shame increased in both conditions, Time: F(1,56)=4.89, p=.032, p 2
=.08, and did not differ between conditions, F(1,56)=2.41, p=.126, p
2
=.04. Control did not change significantly, F(1,57)=.02, p=.889, p2<.01. Tension did not decrease significantly within subjects, F(1,57)=.96 p=.331, p
2
=.02, but, interestingly, there was a significant interaction effect between Time X Condition; participants in the ImRs condition reported a decrease in tension from baseline, while the participants receiving IE displayed increased tension following intervention, Time X Condition: F(1,57)=4.07, p=.048, p
2
=.07.
3.2.3. Day III. Reactivation 2: Test
To compare return of negative emotion in the two conditions, a repeated measures ANOVA with within-subject factor Time (baseline 3 vs. reactivation 2) and between-subject factor Group (ImRs vs. IE) was carried out. There were significant effect of Time on all dependent variables; negative affect, F(1,56) = 14.17, p<.001, p2=.2, state anxiety, F(1,54) = 90.88, p<.001, p2=.63, shame,
F(1,57)=17.81, p<.001, p 2 =.24, anger, F(1,57)=12.19, p=.001, p 2 =.17, tension, F(1,57)=74.91, p<.001, p 2 =.57, ECG, F(1,53)=18.94, p<.001, p 2 =.26, and SCL, F(1,55)=48.26, p<.001, p 2 =.47, and decreases in positive affect, F(1,54)=26.27, p<.001, p
2
=.33 and control, F(1,57)=38.16, p<.001, p
2
=.4. This indicates that the expectation of having to perform tasks in front of a panel again elicited a physiological and subjective response across participants, as was expected. However, unexpectedly, no significant differences between conditions were found, on state anxiety, negative affect or positive affect, shame, anger, control, tension, fear, or physiological responses in heart rate of skin
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conditions on the post-experimental questionnaire. Participants in the two conditions were equally likely to come back for another TSST and equally dreaded doing the stress task again if asked to do so, all Fs≤.146, all ps≥.7.
Figure 3. ECG responses over the three days of the experiment.
Figure 4. SCL values over the three days of the experiment.
0 0,5 1 1,5 2 2,5 3 3,5 4 4,5
Day 1: TSST Day 2: Imagery Day 3: Test
Changes in ECG from baseline (z-values)
IE IMRS 0 0,5 1 1,5 2 2,5
Day 1: TSST Day 2: Imagery Day 3: Test
Changes in SCL from baseline (z-values)
IE IMRS
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4. Discussion
The present study aimed to investigate the return of negative emotion following different imagery interventions within a new complex emotional learning paradigm, using the Trier Social Stress Test as a means of acquiring negative emotional memory. As expected, the Trier Social Stress Test induced an aversive memory event that could be retrieved and physiological as well as subjective negative emotions towards the TSST could be reactivated 24h and 48h afterwards. Therefore, the TSST seems to be a suitable instrument in emotional memory research, bridging the gap between experimental associative learning research (i.e., fear conditioning paradigms) and the pathogenesis of fear and anxiety outside the laboratory.
The expected difference between imagery rescripting and imaginal exposure in decreasing negative emotional reinstatement was not found. This finding can be interpreted in different ways: First, it might be possible that even though ImRs is proposed to underlie different working
mechanisms than IE, the two therapeutic techniques are not as different as we think they are. Second, perhaps the ImRs intervention was not successful. Again, this might be due to several reasons: First of all, in ImRs, expression of inhibited trauma-related emotions is facilitated (Arntz, Tiesema & Kindt, 2007). In the set-up of the present experiment, the intervention took place in the same room as the stress-inducing TSST and was conducted by the experimenter who also gave the instruction for the TSST on day I. Therefore, by the experimenter taking on a double role as both ‘perpetrator’ and ‘therapist’, it may be the case that ImRs was not optimally conducted, perhaps because participants associated the experimenter with the stress task itself and could not express, for example, their anger, as is hypothesised to enable replacing feelings of victimisation with feelings of mastery (Arntz & Weerman, 1999). The participants in the ImRs condition were significantly angrier than their IE counterparts after the TSST. By not facilitating optimal execution of ImRs and expression of this anger, the intervention may have been more similar to IE, minimising potential differences in effect due to the underlying working mechanisms.
Another potential difficulty of the present set-up is that the stress task, the intervention and the test all took place in the same laboratory. Exposure is known to be context-dependent (for reviews see Bouton, 2004; Craske et al., 2008). A robust phenomenon that represents a vulnerability of
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exposure therapy, the renewal effect, often occurs after exposure. When an association is learned in context A and exposure takes place in a different context B, fear often returns when one is confronted with context A again: the original learned association between a conditioned, previously neutral and an unconditioned, aversive stimulus, is retrieved, and elicits responses. The association formed during exposure, where the conditioned stimulus was no longer paired with an aversive stimulus and
responses decreased, cannot be retrieved in the changed context (Dibbets, Poort & Arntz, 2012). This effect is well documented in both animal and human learning research (Effting & Kindt, 2007). ImRs has been found to generalise to different contexts and stimuli and reduce fear renewal in an ABA-paradigm (Dibbets, Poort & Arntz, 2012). In the present study, the context was slightly different during reactivation and intervention (i.e., lights were dimmed), but this is conceivably not a big change. The participants were seated at the same table, again facing the table where the panel sat during the TSST and the video-camera. Instructions for the test on the last day of the experiment mentioned “new tasks before a new panel”, but verbal reactions of participants at the end of the experiment suggested this detail was often overlooked. Assuming the contexts did not differ, we can conclude that even in the same context as the intervention took place, where both imagery rescripting and the context-dependent imaginal exposure are expected to solicit a therapeutic effect, the test elicited a return of negative emotion. This is positive news concerning the suitability of the paradigm, showing the TSST induces a memory that can be retrieved forty-eight hours later, but it also raises the question whether either of the interventions was successful. At the moment, we have no way of answering this question, since the present study lacked a control condition. Our results match those of earlier studies, were treatment effects of ImRs were found using a very similar protocol (Hagenaars & Arntz, 2012). This gives us reason to believe that our imagery interventions did affect the emotional responses of the participants. Perhaps the measures used in our study are not suitable to detect differences in effect of the two interventions. However, to be able to not only compare the effects of ImRs and IE on the return of negative emotion, but also see whether the interventions have any therapeutic effect at all, a control group undergoing an imagery intervention unrelated to the stress manipulation should be added to the design in future research. If both interventions are effective, it is
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very well possible that by creating an ABA-context, (i.e., intervention and test take place in different contexts) a difference in effect could be found between IE and ImRs.
Third, the three day set-up of the study may have posed an additional problem. Research into debriefing practices, in which victims receive psychological care immediately and before potential symptoms develop, has failed to show efficacy. Against intuitive appeal, debriefing can even have detrimental effects on the psychological wellbeing of victims of different traumas (Van Emmerik, Kamphuis, Hulsbosch & Emmelkamp, 2002; Kaplan, Iancu & Bodner, 2001). Perhaps in our study the twenty-four hour period between the negative event and the intervention was too short for the interventions to elicit an effect.
Fourth, several characteristics of the research sample may have complicated finding a difference between the effects of the imagery interventions. The participants in this study were students receiving a reward for their cooperation. It is possible that this has influenced their
motivation and investment, and therefore the scope of their emotional reactions. As the present study tried to provide an analogue to the development and treatment of anxiety in real life, emotional investment at the various stages of the study was crucial. Personal relevance of the analogue trauma in this laboratory setting may have been too limited. Perhaps in a future experiment, selecting
participants experiencing greater personal relevance to a certain stimulus, for example participants who have lived through an actual traumatic experience, or, in the case of the TSST, participants with a fear of giving presentations, may heighten emotional relevance and enhance the effectiveness of the interventions. This could result in a sample with higher autonomous motivation, i.e. whether patients experience participation in therapy as their own free choice, a factor that is known to be an important predictor of therapeutic outcome (Zuroff, Koestner, Moskowitz, McBride, Marshall, & Bagby, 2007). Although a difference in effect between the two interventions was not found, ImRs did turn out to reduce subjective levels of distress significantly more than IE did. This might be due to a demand effect: In ImRs, participants were asked to change the course of events in such a way that it was less disturbing to them, and keep doing this until it felt acceptable to them. However, this instruction did not lead to a decrease in subjective distress in all participants undergoing ImRs, indicating a demand effect cannot explain all variation. Also, the ImRs intervention was rated as
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significantly more pleasant and agreeable than the IE intervention. The fact that ImRs is perceived as a less aversive treatment than IE is an important advantage of ImRs, as it might enhance therapeutic compliance and reduce drop-out rates (Arntz, Tiesema & Kindt, 2007; Hagenaars & Arntz, 2012). In a field were drop-out is quite common, this is an important characteristic (Hembree, Foa, Dorfan, Street, Kowalski & Tu, 2003).
In conclusion, this experimental study introduces a valuable new paradigm to investigate complex emotional learning and therapeutic interventions for aversive emotional memories in an experimental setting while maintaining high external and ecological validity compared to traditional learning paradigms, such as fear conditioning models. Also, this study showed that one short session of ImRs lowers distress experienced when the traumatic memory is reactivated and is more agreeable and pleasant than a short session of IE. Therefore, ImRs may be a promising alternative in the treatment of psychological distress as a result of traumatic experiences.
Acknowledgements
The authors would like to thank Maya Berger, Sophie Black, Wendy Kuijn and Arved Stucke for their assistance during data collection.
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