Participants
The authors performed a secondary analysis of data from databases built during the previous research project, “Neuropsychological and Social Institutional Foundations for Prosocial Behavior” (http://www.human-sociality.net/english/), conducted between 2012 and 2018. About 400 adults living near Tamagawa University participated in the project, which involved a series of experiments in which they played economic games that measured prosocial behavior and completed various psychological scales and cognitive tasks. Furthermore, MRI and genetic polymorphism data were collected. Since the experiments were not conducted on the same schedule from wave 1 to wave 3, participants were not asked to complete the MRI and similar questionnaires every time. Samples were collected using the following configuration. Overall, 470 participants (244 males) aged 19–59 years (mean ± standard deviation [SD] = 40.09 ± 10.77 years) took part in the previous research project. Among them, 405 participants underwent MRI and answered the one-item simple subjective well-being questionnaire and 16-item Promotion/Prevention Focus Scale (PPFS) in 2012–2013 (wave 1) and answered the 11-item Regulatory Focus Questionnaire (RFQ) in 2014–2015 (wave 2). Among them, 286 participants answered the five-item Satisfaction with Life Scale (SLS) evaluating subjective well-being in 2018 (wave 3). Altogether, 277 participants completed the MRI, regulatory focus, and subjective well-being questionnaires.
Measurement of subjective well-being and regulatory focus
This study used the SLS to evaluate participants’ subjective well-being (Diener et al. 1985) in wave 3. The participants answered the questions using a six-point scale, ranging from “strongly disagree” to “strongly agree,” with the average score representing the degree of life satisfaction. The five questions were as follows: (1) In most ways, my life is close to my ideal; (2) The conditions of my life are excellent; (3) I am satisfied with my life; (4) So far, I have gotten the important things I want in life; and (5) If I could live my life over, I would change almost nothing. Furthermore, this study also used the one-item simple subjective well-being questionnaire to assess participants’ subjective well-being simply in wave 1. The question was as follows: “Do you think your life is a happy life?” The participants answered the question using a six-point scale, ranging from “I think I spend an extremely unhappy life” to “I think I spend an extremely happy life.”
In order to assess the regulatory focus of the participants, two representative questionnaires, PPFS and RFQ, were administered in waves 1 and 2, respectively. This study used the RFQ to evaluate participants’ trait promotion and prevention focus in wave 2 (Higgins et al. 2001; Matsuoka et al. 2021). The participants answered 11 questions using a five-point scale, ranging from “strongly disagree” to “strongly agree,” and the scores for the five prevention focus and six promotion focus items were totaled and divided by the number of items to give the prevention focus and promotion focus scores, respectively. The five prevention focus items were as follows: (1) Growing up, would you ever “cross the line” by doing things that your parents would not tolerate? (2) Did you often get on your parents’ nerves when you were growing up? (3) How often did you obey rules and regulations established by your parents? (4) Did you ever act in a way that your parents thought was objectionable? and (5) Not being careful enough has sometimes caused trouble. The six promotion focus items included: (1) Compared to most people, are you typically unable to get what you want out of life? (2) How often have you accomplished things that got you “psyched” to work even harder? (3) Do you often do well with the different things that you try? (4) When it comes to achieving things that are important to me, I find that I do not perform as well as I ideally would like to; (5) I feel like I have made progress toward being successful in my life; and (6) I have found very few hobbies or activities in my life that capture my interest or motivate me to put effort into them.
This study used the PPFS to evaluate participants’ trait promotion and prevention focus in wave 1 (Lockwood et al., 2002). There are 18 items for the original paper, but in this study, 16 items were used with two items that were only applicable to students removed. The participants answered 16 questions using a five-point scale, ranging from “strongly disagree” to “strongly agree,” and the scores for the eight prevention focus and eight promotion focus items were totaled and divided by the number of items to give the prevention focus and promotion focus scores, respectively. The eight prevention focus items were as follows; (1) I am anxious that I will fall short of my responsibilities and obligations; (2) I often think about the person I am afraid I might become in the future; (3) I often worry that I will fail to accomplish my academic goals; (4) I often imagine myself experiencing bad things that I fear might happen to me; (5) I frequently think about how I can prevent failures in my life; (6) I see myself as someone who is primarily striving to become the self I “ought” to be—to fulfill my duties, responsibilities, and obligations; (7) I am more oriented toward preventing losses than I am toward achieving gains; and (8) In general, I am focused on preventing negative events in my life. The eight promotion focus items included: (1) I frequently imagine how I will achieve my hopes and aspirations; (2) I often think about the person I would ideally like to be in the future; (3) I typically focus on the success I hope to achieve in the future; (4) I often think about how I will achieve academic success; (5) I see myself as someone who is primarily striving to reach my “ideal self”—to fulfill my hopes, wishes, and aspirations; (6) In general, I am focused on achieving positive outcomes in my life; (7) I often imagine myself experiencing good things that I hope will happen to me; and (8) Overall, I am more oriented toward achieving success than preventing failure.
Magnetic resonance imaging data collection
MRI data were collected using a 3T Siemens Trio A Tim MRI scanner. High-resolution anatomical images were acquired using a T1-weighted 3D magnetization-prepared rapid acquisition gradient echo sequence (repetition time, 2,000 ms; echo time, 1.98 ms; field of view, 256 × 256 mm; number of slices, 192; voxel size, 1 × 1 × 1 mm; average, 3 times).
Voxel-based morphometry (VBM) analysis
T1-weighted images were processed and analyzed using the Computational Anatomy Toolbox (CAT12; http://dbm.neuro.uni-jena.de/cat/) and Statistical Parametric Mapping software (SPM12; http://www.fil.ion.ucl.ac.uk/spm). The images were bias-corrected, marked for tissue or fluid type (gray matter, GM; white matter, WM; and cerebrospinal fluid, CSF), and registered using linear (12 parameter affine) and nonlinear (warping) transformations within the default preprocessing pipeline of CAT12. Diffeomorphic Anatomical Registration Through Exponentiated Lie Algebra (DARTEL) (Ashburner 2007) was used for spatial normalization of the Montreal Neurological Institute (MNI) space. This initial step generated modulated normalized images that were smoothened using a standard SPM12 smoothing pipeline with a full-width-at-half-maximum smoothing kernel measuring 8 × 8 × 8 mm. CAT12 was used to estimate the overall volumes of the GM, WM, and CSF. These pre-treatment procedures are similar to those used in extensive MRI studies in children (Sheffield et al. 2021).
The preprocessed smoothened GM images were analyzed using SPM12 to ascertain the brain regions where GM density was associated with subjective well-being and tendencies of regulatory focus. A multiple regression analysis was performed using rating scores of subjective well-being, promotion focus, and prevention focus as independent variables. The participants’ age, sex, and total intracranial volume were included in the analysis as covariates of no interest to regress any attributable effects. The authors conducted region of interest (ROI) analyses using the Automated Anatomical Labeling (AAL) Atlas (Caudate_L and Caudate_R) (Tzourio-Mazoyer et al. 2002) in the Wake Forest University PickAtlas Toolboxes (Maldjian et al. 2003) for SPM12. The statistical threshold was set at p < 0.005 at the voxel level for an uncorrected p-value and p < 0.05, at the cluster level (ROI) for a family wise error (FWE) corrected p-value. The parameter estimates were then extracted from MATLAB and used to create scatter plots and conduct a mediation analysis.
Statistical analyses
Psychological data were analyzed using SPSS version 27 (IBM Corp., Armonk, NY, USA). The normality of the data (subjective well-being and regulatory focus) was analyzed using the Shapiro-Wilk test, and Spearman’s rank correlation coefficient was calculated to reveal the correlation between rating scores for subjective well-being and regulatory focus. Furthermore, a mediation analysis was conducted using the PROCESS macro, version 3.5.3 (Hayes 2022), in which models predicting future subjective well-being were mediated by promotion orientation (Model 4, i.e., simple mediation by a single variable). The mediation model was estimated using default bootstrapping procedures (10,000 samples).