Participants
Participants were recruited through flyers and emails from several Universities in India. General inclusion criteria were that students should be 18 years of age and have a good command of English. Table 1 provides participants’ demographics. The sample comprised 88 students (Mage = 21.77 years, SD = 2.31; 50% Females). Participants were then divided into two groups: a sub-clinical pain group (N = 40) and a control group (N = 48). The criterion to be included in the sub-clinical pain group was to have a score above the clinical cut-off of 1.77 on the pain subscale based on the manual of Symptom Checklist-27-plus [22]. The cut-off is the official cut-off specified in the manual. The type of effect size used in our study is Partial eta squared (η2p), estimated to be 0.027 based on our previous study [8], which investigated differences in mood and behavioral responses to reward between students with sub-clinical pain symptoms and healthy controls using an ANOVA. We used the recommendations formulated by Lakens [23] to enter the parameters in G-Power using a partial eta squared (η2p) of 0.027, which led to the estimated Cohen’s F value of 0.17. Using G-Power, the estimated sample size needed would be 80 to have the actual power with 5% alpha error, 95% power, and p < 0.05 as the significance level for the ANOVA with repeated measures and within-between interaction. Both groups did not differ in depression and anxiety.
The study was approved by the Institutional Review Board at the University of Fribourg in Switzerland (2017/IRB 334A). Participants were thoroughly informed about the study and gave their electronic consent. All research was performed according to the Declaration of Helsinki. The privacy rights of participants were always observed during our study.
Procedure
Students completed a battery of questionnaires online using LimeSurvey® (LimeSurvey GmbH, Hamburg, Germany. URL http://www.limesurvey.org) as well as an adapted online version of the Fribourg reward task [8, 21]. The participants were allowed to terminate the survey at any time they desired. The survey was anonymous, and confidentiality of information was maintained.
Psychometric Measures
Symptom Checklist (SCL-27-plus) for pain:
Symptom Checklist (SCL-27-plus; [28]) is a multidimensional assessment instrument for mental health status [24]. With 27 items rated on a 5- point Likert-type scale, it consists of five dimensions: depressive, vegetative, agoraphobic, social phobia, and pain symptoms. A lifetime assessment of depressive symptoms and a screening question for suicidality are also included. Participants rated the following pain symptoms: headaches, chest pain, muscle cramps, muscle aches, arm/leg pain, and lower back pain for 0 “never” to 4 “very often” on a pain subscale depending on how often these symptoms occur in past two weeks. A value of 0 stood for “never”, 1 stood for “1-2 days”, 2 for “3-7 days”, 3 for ”8-12 days”, and 4 for “13-14 days”. A mean score of ≥1.77 indicates physical symptoms of pain according to SCL-27 [22]. Previous studies reported significant pain symptoms in university students using the SCL-27 [8, 25, 26]. The overall Cronbach’s alpha coefficient in this study was 0.87, which is very high.
Hospital Anxiety and Depression Scale
Hospital Anxiety and Depression Scale (HADS [27, 28] is a self-assessment scale that consists of a 14-item scale (7 relating to anxiety symptoms and 7 to depression); each item is coded 0 to 3. The total score can range from 0 up to 42. The clinical cut-off score on depression or anxiety scales is equal to or greater than 11 on any symptoms. The overall Cronbach’s alpha coefficient in this study was 0.80, which is very good.
Fribourg Reward Task
We used an online adapted behavioral version of the Fribourg reward task [21] to measure reaction times, and mood reactions to monetary reward. Neuroimaging studies using this task have successfully elicited neural activation in regions associated with the cerebral reward system [29], including the striatum, a putative region for reward processing. In short, the task was originally programmed using E-Prime software (version 1.1.3, Psychology Software Tools Inc., Pittsburg, Pa., USA) and made available online using OpenSesame, a graphical experiment builder for the social sciences. The experimental task was presented in three block conditions, comprising of reward conditions (monetary reward, social reward, and no-reward). Here, we focus only on the monetary versus no-reward conditions to investigate whether physical symptoms of pain affect the responses to monetary reward in Indian students as we evidenced in Swiss students [8]. Each block condition consisted of 12 trials each and the order of the blocks was pseudo-randomized. In the three-reward conditions, at the onset of each trial (see Fig.1), a visual cue (1500 ms) was presented (3 yellow circles), along with the reward associated with performance. After the presentation of a fixation cross (500 ms), participants saw an array of yellow circles (3 circles, 1500 ms). A fixation cross (3000 ms) was presented before the visual target (1500 ms). The visual target (a green circle) was displayed in any position on the screen and signaled that the participant should decide as quickly as possible whether this circle was in the same position as one of the circles presented previously. After response execution and a variable jittered interstimulus interval (ISI; 0 ms or 2000 ms), the feedback screen (1000 ms) informed the participant of his or her winnings. For the monetary reward condition, a screen with “Rs 0” was shown for incorrect trials or “Rs 10” for correct trials, in the social reward condition, a “neutral” face smiley was shown for incorrect trials or a “win” face smiley for correct trials and in the no-reward condition, a blank screen was shown for every correct or incorrect trial. In the end, a feedback screen (1000 ms) indicating the cumulative amount of monetary reward or social reward (smileys) earned (in the monetary and social reward conditions) or a blank screen in the no-reward condition. Correct responses were associated with monetary gains (“Rs 10” for participants in India) in the monetary reward condition. Correct responses were not associated with any gains in the no-reward condition. We asked participants to rate their momentary mood and stress level using a visual analog scale from 0 (bad mood) - 10 (good mood). With smileys at the anchor points (0=
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alt="Shape, circle
Description automatically generated"> ). Participants rated their momentary mood and stress level on a scale of 0 to 10 at baseline, at the beginning of the experimental session, and before and after each block for a maximal duration of the 20s. Participants were informed that they would receive the total sum in cash at the end of the session. Participants underwent a training phase before proceeding to the main task. A criterion of 70% correct responses was chosen to prevent arbitrary guessing and thereby verify understanding of the task and ensure that participants would win similar amounts of money.
Data Analysis
Analyses were calculated using IBM SPSS Inc 25. Normality tests were performed for mood and reaction time, and the data were found to be normally distributed using Shapiro-Wilk Test (p > 0.05). Descriptive statistics are presented in Table 1 for the two groups. Baseline mood ratings were compared among the groups using t-tests. We also performed exploratory analyses comparing the mean mood ratings between groups in the no-reward conditions to test the specificity of our results. To test the effect of reward on mood in participants in the sub-clinical pain group and the control group, a repeated-measures ANOVA was conducted, using mood as the dependent variable, with the following factors: groups (with pain symptoms and without clinically significant pain symptoms) as a between-group factor, reward conditions (reward and no-reward) as within group factors. Additional mixed ANOVA using the same factors was applied using reaction time as the dependent variable to test the effect of reward on performance and to compare the possible performance differences between the two groups of participants.
In addition, we postulated that there would be a significant positive correlation between mood ratings and monetary gains in the reward condition in the control group, but not in the sub-clinical group based on our previous study [8]. To test this hypothesis, the Pearson product-moment correlation between mood scores and monetary wins in reward conditions was performed separately in each group of subjects according to similar studies done previously [8, 21, 30].