Effect of cortical thickness on later donating behavior in
middle childhood between boys and girls
Daphne van Mierlo; Universiteit van Amsterdam
Abstract
Prosocial behavior is an important concept of social life. However, the effect of neuroanatomical correlates on independent concepts of prosocial behavior is largely unknown. Furthermore, there are conflicting results in the literature about sex differences in prosocial behavior and cortical thickness of different cortical regions. Therefore, the present study examined whether there is an effect of cortical thickness on donating behavior in middle childhood and whether this effect differs between sexes. The present study especially looks at cortical thickness of the following brain areas whose were associated with prosocial or donating behavior in previous research (right superior frontal cortex, left superior frontal cortex, right superior parietal cortex, right rostral middle frontal cortex, left rostral middle frontal cortex, right lateral orbitofrontal cortex, right pars orbitalis cortex, right precentral cortex, and right postcentral cortex). To gain more insight in the effect of cortical thickness on donating behavior in middle childhood, the study included 151 children (53.6% girls) with an average age of 8.00 (SD = 0.67, range = 7.02 – 9.68 years) years old at time point 1 and an average age of 10.06 (SD = 0.68, range = 8.97 – 11.67 years) years old at time point 2. For the measure of cortical thickness, MRI data was used, and a donating task was used to assess donating behavior. Analyses were performed for boys and girls separately. Results imply there is no significant effect of cortical thickness in all nine investigated ROIs on donating behavior in both boys and girls. Furthermore, there was no sex difference observed in the relation between cortical thickness and donating behavior in middle childhood. These findings suggest that cognitive processes related to donating behavior and cortical thickness in regions that were related to prosocial and donating behavior could be underdeveloped. Furthermore, findings in the present study suggest that donating behavior could be more influences by environment characteristics instead of cortical thickness.
1. INTRODUCTION
Prosocial behavior is an important concept of social life and is defined as voluntary behavior that intentionally benefits another person (Eisenberg et al., 2013). The development of prosocial behavior starts in early childhood, where some simple concepts of prosociality are observed, and continues into adulthood (Brownell, 2013; Dunfield et al., 2011; Schachner et al., 2018; Warneken and Tomasello, 2006). Several studies showed that prosocial behavior is associated with cortical thickness in middle childhood to young adulthood (Ferschmann et al., 2019; Thijssen et al., 2015; Wildeboer et al., 2018) and that this association could be moderated by sex in middle childhood (Thijssen et al., 2015). However, whether cortical thickness influenced prosocial behavior or vice versa remains unclear as well as it remains unclear whether the relation between cortical thickness and prosocial behavior differs between sexes. Studying this relation between cortical thickness and prosocial behavior and sex differences in middle childhood might provide more insights into normal prosocial behavior and disorders. For example conduct disorder, where the issue is a lack of prosocial behavior and where previous research showed symptom differences between sexes (Berkout et al., 2011) and cortical thickness differences between healthy females and females diagnosed with conduct disorder (Budhiraja et al., 2019). Therefore the current study investigated the effect of cortical thickness on donating behavior (a specific form of prosocial behavior) in middle childhood and whether this differs between sexes.
Although prosocial behavior is widely investigated, a limited number of studies examined sex differences in donating behavior and the relation to neuroanatomical correlates in middle childhood. Studies showed that girls exhibit more prosocial behavior than boys in 6-to-9 years old children (Thijssen et al., 2015) and adolescence to young adulthood (Ferschmann et al., 2019). However, there is disagreement over the developmental trajectory of prosocial behavior. For example, Van der Graaff et al. (2018) showed differences in the developmental process of prosocial behavior between boys and girls in adolescence, while another study demonstrates no difference in the trajectory of prosocial development between sexes in adolescence to young adulthood (Ferschmann et al., 2019). Therefore, more longitudinal studies should investigate the course of prosocial development between sexes.
Besides the incongruent findings of the course of prosocial development between sexes, there are some conflicting outlines about sex differences in the neurodevelopmental trajectory of regional cortical thickness as well. Several studies showed sex-related differences in the developmental course of cortical thickness, including cortexes of the social brain, studying a sample from 5-to-22 years old and 9-to-30 years old (Mutlu et al., 2013; Raznahan et al., 2010). However, in contrast to these findings, various studies did not observe sex differences in the mean neurodevelopmental trajectory of the cortical thickness (Raznahan et al., 2011; Wierenga et al., 2019). Although there are several contradictions about sex differences in prosocial behavior and the development of cortical thickness, Thijssen et al. (2015) found a sex modulation effect in the association between cortical thickness and prosocial behavior in middle childhood. Thijssen et al. (2015) showed that a thicker cortex in the cluster contained the right superior parietal cortex as well as in the cluster covering the right rostral middle frontal, and superior frontal cortex was associated with more prosocial behavior in boys. In girls, the association between the thickness of the cortexes in these two clusters and prosocial behavior was negative. Besides these two clusters, a thicker cortex in the cluster, including parts of the left superior frontal and rostral middle frontal cortex, was associated with more prosocial behavior in both boys and girls (Thijssen et al., 2015). However, it has to be mentioned that these findings were based on prosocial behavior measured by a parental-questionnaire, including multiple constructs of prosocial behavior. Previous research observed that different independent constructs of prosocial behavior (e.g., helping, sharing, comforting, donating) were related to different socio-cognitive and neurobiological mechanisms in childhood (Dunfield et al., 2011; Dunfield and Kuhlmeier, 2013; Paulus, 2014a; Steinbeis, 2018). Therefore, the present study focused on one specific construct of prosocial behavior, which is donating behavior.
As mentioned above, the present study focused on donating behavior as a specific construct of prosocial behavior. Donating behavior is mostly investigated among adults as well as sex differences in donating behavior. For example,Andreoni, Brown & Rischall (2003) showed that there were significant sex differences in the amount they donate and their tendency to donate in single adult women and men. However, whether donating behavior differs between sexes in middle childhood is largely unknown. Moreover, not only sex differences in donating behavior in middle childhood are largely unknown, but donating behavior itself in middle childhood has also been investigated to a limited extent. One study observed that the consideration of donating to a charity was present in children around five years old (Paulus, 2014b). Furthermore, other studies showed that the feeling of
happiness in children increased when they give treats to a puppet compared to when the children receive treats themselves from an experimenter (Aknin et al., 2015, 2012). This feeling of happiness was also found in neuroimaging studies in adults, where the neural reward system became more activated during the decision for a charitable donation (Hare et al., 2010; Moll et al., 2006). Furthermore, a study observed that brain activation in the ventral striatum predicted voluntary charitable giving in adults (Harbaugh et al., 2007). However, whether brain morphology measures could predict donating behavior remains unclear, as well as whether this is already presented in middle childhood. Only one study has investigated the neuroanatomical correlates of donating behavior in 8-years old children (Wildeboer et al., 2018). Associations were observed between donating behavior and cortical thickness of a cluster covering parts of the right lateral orbitofrontal cortex and the pars orbitalis and a cluster covering parts of the right precentral and postcentral cortex (Wildeboer et al., 2018). However, whether cortical thickness influenced donating behavior or vice versa remains unclear. Therefore, the present study investigated the effect of cortical thickness on donating behavior in middle childhood.
Taken together, there were two studies showing associations between cortical thickness of clusters covering parts of the frontal and parietal cortexes and prosocial and donating behavior in middle childhood (Thijssen et al., 2015; Wildeboer et al., 2018). However, whether cortical thickness influenced prosocial/donating behavior or vice versa remains unclear. Earlier research observed that the cortical thickness in the dorsolateral prefrontal cortex could predict prosocial choices in economic games in adults (Yamagishi et al., 2016). Therefore, the present study examined with data of 151 children (53.6% girls) what the effect is of cortical thickness on donating behavior two years later in middle childhood and whether this effect is different between sexes. Donating behavior is measured two years later than the cortical thickness because the longitudinal effect of cortical thickness on donating behavior could be investigated to observe whether beginning stages of cortical thickness related to donating behavior could predict later more developed donating behavior. The measure of cortical thickness was obtained with Magnetic Resonance Imaging (MRI) scans when the children were on average of 8.00 (SD = 0.67, range = 7.02 – 9.68 years) years old. Two years later, the measure of donating behavior was obtained with an donating task when the children were on average 10.06 (SD = 0.68, range = 8.97 – 11.67 years) years old. The present study included the cortical thickness of nine cortexes which were associated with prosocial or donating behavior in middle childhood: 1) right superior frontal cortex, 2) left superior frontal cortex, 3) right superior parietal cortex, 4) right rostral middle frontal cortex, 5) left rostral middle frontal cortex, 6) right lateral orbitofrontal cortex, 7) right pars orbitalis cortex, 8) right precentral cortex, and 9) right postcentral cortex (all based on findings of Wildeboer et al. (2018) and Thijssen et al. (2015)). The present study hypothesized that a thicker cortex of all cortexes except the right rostral middle frontal, right superior frontal cortex and right superior parietal cortex predict higher charity donations two years later in both boys and girls. Secondly, the present study hypothesized that a thicker cortex of the right rostral middle frontal, right superior frontal cortex and right superior parietal cortex predict higher charity donations two years later in boys and, in contrast to boys, that a thinner cortex of these three cortexes predicts higher charity donations two years later in girls.
2. METHOD
2.1 ParticipantsThis study is part of a large longitudinal twin study of the Leiden Consortium on Individual Development (L-CID). The L-CID study recruited participants from municipality records. The recruited families lived in the Western region of the Netherlands and had a twin born between 2006 and 2009 (Euser et al., 2016). Only same-sex twin pairs were included. Other inclusion criteria were normal (or corrected to normal) vision, fluently Dutch spoken parents, and the parents and grandparents had to be born in Europe. Families were excluded when a participant did suffer from a physical or psychological disorder, which could hinder the performance of the tasks. The L-CID study was ethical approved by the Central Committee on Research Involving Human Subjects (CCMO). Before the first baseline assessment, written informed consent was obtained from the parents of the twins.
The present study had access to data of 256 participants, which were selected at random from 256 twin pairs as part of the L-CID study (51.2% girls). Ninety-one participants were excluded due to missing magnetic resonance imaging (MRI) data and/or missing donating behavior data (35.5%). Another 14 participants were excluded because they did not donate within the fixed amount of time (n=11), or there was a misunderstanding about the task (n = 3). These exclusions resulted in a final sample with 151 children (53.6% girls) with an average age of 8.00 years old (SD = 0.67, range = 7.02 – 9.68 years) at the first time point and an average age of 10.06 years old (SD = 0.68, range = 8.97 – 11.67 years) at the second time. The intelligence quotient (IQ) was estimated by two sub-scales (Similarities and Block Design) from the Wechsler Intelligence Scale for Children 3rd version (WISC-III). The estimated IQ scores were within a normal range (72.5 – 137.5), with an average of 103.96 (SD = 11.87). Further analysis was done separately for 70 boys and 81 girls (see Table 1 for an overview of the sample characteristics).
To check whether the boys and girls sample differs in sample characteristics, different analysis were performed. These analysis between boys and girls showed no significant difference in IQ score, t (122.92) = - 0.34, p = 0.73, handedness at time point 1, X2 (1, N = 151) = 0.02, p = 0.88, handedness at time point 2, X2 (1, N = 151.) = 0.34, p = 0.56, SES at time point 1, X2 (2, N = 151) = 4.20, p = 0.12, SES at time point 2, X2 (2, N = 151) = 3.84, p = 0.15. Furthermore, age did not differ significantly between boys and girls at time point 1, W = 2861, p = 0.92, and at time point 2, W = 2964, p = 0.66.
SES = Socio-economic status (based on the education level of both parents)
The Intelligence Quotient (IQ) score was obtained via the WISC-III only at Time Point 1.
When the SES or handedness at Time Point 2 was missing, the values from Time Point 1 were used.
Time Point 1 Time Point 2 Time Point 1 Time Point 2
Age (mean (SD)) 7.98 (0.64) 10.03 (0.64) 8.01 (0.70) 10.08 (0.71)
Range (min - max) 7.04 - 9.07 9.04 - 11.23 7.02 - 9.68 8.97 - 11.67
SES (n (%)) High SES 32 (46.4) 33 (47.8) 41 (50.6) 41 (50.6) Low SES 3 (4.3) 3 (4.3) 10 (12.3) 10 (12.3) Middle SES 34 (49.3) 33 (47.8) 30 (37.0) 30 (37.0) Handedness = Right (n (%)) 62 (88.6) 62 (88.6) 70 (86.4) 68 (84.0) IQ (mean (SD)) 104.32 (13.85) NA 103.64 (9.92) NA
Range (min - max) 72.5 - 137.5 NA 77.5 - 125 NA
Boys Girls
n = 70 n = 81
2.2 Procedure
At both time points, the visit procedure was the same and took place at the Leids Universitair Medisch Centrum (LUMC) were the laboratory visits took place. The follow-up time between the first and second laboratory visits had an average of 2.06 years (SD = 0.10). First, there was an explanation about the visit and the procedure of the MRI scan. To familiarize the children with the MRI procedure and in preparation to reduce head motion during the MRI session, the children had a practice session in a mock MRI scanner. The laboratory visits included a scanning session and a session with behavioral measures. During the MRI session, the children first performed two functional magnetic resonance imaging (fMRI) tasks. After this, a high-resolution structural scan, a Diffusion Tensor Imaging (DTI) scan, and a resting state scan were collected. Besides the MRI scans, the children performed behavioral tasks included the donating behavioral task and answered questionnaires. The laboratory visits lasted about three and a half hours. After the laboratory visits, there was a financial
compensation of 80 euros for the whole family, a travel allowance, and the children receive a gift.
2.3 Donating behavior
Donating behavior was assessed using a donating task where all children received €2,00 (20 coins of 10 euro-cent) at the beginning of the task. It was made clear that the children received the 2 euros as a consequence of an earlier money decision task during the laboratory visit. The children watched a charity video of the Liliane fond on a laptop without the researcher. The video showed a boy in extreme poverty with disabilities and how the Liliane Fund wants to help these children to participate as equally and as fully as possible. After the video, a voice-over and text on the screen asked whether the children wanted to donate money to the Liliane Fund. The children had 30 seconds to choose if and how much they wanted to donate money in an in front placed money box, which contained already several coins (see Figure 1 for the set-up of the donating task). After the donation task, the donated money was counted. There were different versions of the video from the Liliane Fund, but although this was not the focus of this study, it had to been taken into account. A random half of the children, 44 boys (62.9%) and 44 girls (54.3%), saw an extended version of the Liliane Fund video. This extended version means, after the charity video, there was a video fragment showing a same-sex-peer supporting the charity and explicitly donated some money in a money box. A Pearson’s Chi-squared test showed the donating behavior of girls did not differ by the charity video version, X2 (2, N = 81) = 2.50, p = 0.29, neither did donating behavior of boys X2 (2, N = 70) = 2.55, p > 0.28. Therefore, the charity video version was not included as a covariate in the analysis for both boys and girls.
A Shapiro-Wilk test showed a significant departure from normality of the donation behavior in girls (W = 0.88,
p = 1.9e-06) and boys (W = 0.87, p = 4.092e-06). Instead of a normal distribution, the donating behavior showed
several peaks. Therefore, for further analysis, the amount of donated money was divided into three categories: low donating behavior (donated 0 – 20% of the received €2,00), middle donating behavior (donated 21 – 79% of the received €2,00) and high donating behavior (donated 80 – 100% of the received €2,00) (see Table 2 for the deviation of the three categories for boys and girls).
2.4 MRI data acquisition
The high resolution 3D T1-weighted anatomical images (TR = 9.8 ms, TE = 4.6 ms, 140 slices; voxel size = 1.17 x 1.17 x 1.2 mm, and FOV = 224 x 177 x 168 mm) were collected using a Philips Ingenia MR 3.0 Tesla scanner in the LUMC with a 32-channel whole-head coil. Within the head coil, there was a use of foam inserts to reduce head movement. During the collection of the anatomical images, a video projection on a screen was visible via an attached mirror to the head coil.
Figure 1: The donating task
This is the set-up of the donating task. The children saw a video from the Liliane Fund played at a laptop. After the video, the children could made a donation in a money box placed in front of them with the money received at the beginning of the task (a total of 20 coins of 10 euro-cent).
Table 2: Deviation three donating categories based on percentage donated money
Boys Girls
Donating behavior (n (%))
Low donating behavior 28 (40.0) 30 (37.0) Middle donating behavior 34 (48.6) 46 (56.8) High donating behavior 8 (11.4) 5 (6.2)
2.5 ROI analyses
Anatomical labeling and tissue classification of the T1 scans was performed in Freesurfer 5.3 software (http://surfer.nmr.mgh.harvard.edu/). Briefly, this software includes tools for removing non-brain tissue, reconstruction of cortical surface, cortical parcellation, subcortical segmentation, and estimation of various measures of brain morphometry. Technical details of the processing of the T1 scans performed in Freesurfer are described in prior research (Dale et al., 1999; Fischl et al., 2001, 1999; Fischl and Dale, 2000). The measures of cortical thickness were estimated by the average distance between white matter surfaces and pial surfaces (Figure 2; reprinted from (Wierenga et al., 2014)). For extraction of cortical thickness (in mm) measures in our Regions of Interest (ROI), the Desikan-Killiany atlas (DK atlas; Desikan et al., 2006) was implemented. Figure 3 (created with BrainNet (Xia et al., 2013)) illustrated the ROIs, which were selected based on prior research with a whole-brain analysis (Thijssen et al., 2015; Wildeboer et al., 2018). These ROIs included the right lateral orbitofrontal cortex, right pars orbitalis, right precentral cortex, and the right postcentral cortex (correlates of donating behavior in children; Wildeboer et al., 2018). These ROIs also included the left superior frontal cortex and left rostral middle frontal cortex (correlates of prosocial behavior in children; Thijssen et al., 2015), and the right superior parietal cortex, right rostral middle frontal cortex, and the right superior frontal cortex (correlates of prosocial behavior in children modulated by sex; Thijssen et al., 2015). After pre-processing the scans with Freesurfer, the data quality check was assessed using the Qoala-T tool (Klapwijk et al., 2019), which is a supervised-learning tool to reduce rate bias and misclassification.
Figure 3. Illustration of the Regions of Interest
All ROIs are presented from different views and are labeled with a color (see legend)
Note. Created with BrainNet Viewer (version 1.7); Xia, M., Wang, J., He, Y., 2013. BrainNet Viewer: A Network Visualization Tool for Human Brain Connectomics. PLoS One 8.
Figure 2. Representation of cortical thickness Cortical thickness (in mm) is the average distance between white matter surface and pial surface.
Note. Reprinted from Wierenga, L.M., Langen, M., Oranje, B., Durston, S., 2014. Unique developmental trajectories of cortical thickness and surface area. Neuroimage 87, 120– 126.
2.6 Statistical analyses
The data analyses were performed in R (version R-4.0.0) in RStudio (version 1.2.5042) included package “MASS” (Venables and Ripley, 2002). A Welch two-sample t-test, Pearson’s Chi-squared tests, and a Wilcoxon rank-sum test were used for analyses on sample characteristics between boys and girls. Ordinal Logistic Regression analyses between the cortical thickness of each ROI and donating behavior groups were performed to analyze the effect of cortical thickness on donating behavior two years later. This analysis was done for boys and girls separately and was adjusted for baseline age, IQ, and SES. The Ordinal Logistic Regression model is represented in the following formula:
𝑙𝑜𝑔𝑖𝑡 (𝑃(𝑑𝑜𝑛𝑎𝑖𝑡𝑛𝑔 𝑏𝑒ℎ𝑎𝑣𝑖𝑜𝑟 ≤ 𝑗))
= 𝑖𝑛𝑡𝑒𝑟𝑐𝑒𝑝𝑡 − 𝛽𝐶𝑜𝑟𝑡𝑖𝑐𝑎𝑙 𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠 ∗ 𝐶𝑜𝑟𝑡𝑖𝑐𝑎𝑙 𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠 − 𝛽𝐴𝑔𝑒 ∗ 𝐴𝑔𝑒 − 𝛽𝐼𝑄 ∗ 𝐼𝑄 − 𝛽𝑆𝐸𝑆
∗ 𝑆𝐸𝑆
The logit of the probability for reaching at least category j (low, middle, high donating behavior) is calculated with j – 1 equations, because for each transition step between the ordered categories. The intercept term is the intercept value of category j and the 𝛽 term is the regression coefficient value of the predictor (in this analysis, cortical thickness). The analysis was corrected for multiple comparisons with a Bonferroni correction. When the effect of cortical thickness on donating behavior was significant in boys and/or in girls, a Chow’s Test for heterogeneity in two regressions between sexes was performed to investigate whether the effect was significantly different between sexes.
3. RESULTS
There was no significant difference revealed in donating behavior between boys and girls, X2 (2, N = 151) = 1.77, p > 0.41. The analyses to investigate what the effect is of cortical thickness on donating behavior two years later
were conducted with separate analyses for girls and boys for the different ROIs (Figure 3).
3.1 Effect of cortical thickness on donating behavior in girls
An ordinal logistic regression analysis was conducted to investigate the effect of cortical thickness on donating behavior two years later in girls. The analysis showed no significant effect of cortical thickness on donating behavior two years later in girls for all ROIs after a Bonferroni correction and adjusting for baseline age, IQ, and SES (Figure 4 and Table 3).
Figure 4. Representation of relation between cortical thickness and donating behavior in girls
The individual effect of cortical thickness (x-axis) of each ROI on donating behavior (y-axis) for girls. Individuals were classified in high donating behavior (donated 80 – 100% of received money), middle donating behavior (donated 21 – 79% of received money) and low donating behavior (donated 0 – 21% of received money).
Lower (2.5%) Upper (97.5%) Lower (2.5%) Upper (97.5%) rh lateral orbitofrontal -0.41 0.69 -0.60 -1.78 0.94 1.00 0.77 0.77 1.01 -0.69 2.36 1.00 rh pars orbitalis -0.34 0.47 -0.73 -1.27 0.57 1.00 0.42 0.69 0.61 -0.93 1.81 1.00 rh precentral -0.03 0.94 -0.04 -1.90 1.85 1.00 1.62 1.04 1.56 -0.38 3.72 1.00 rh postcentral 0.15 1.29 0.12 -2.40 1.85 1.00 2.33 1.34 1.73 -0.26 5.05 0.75 rh superior parietal -0.73 1.15 -0.63 -2.98 1.57 1.00 2.22 1.11 2.00 0.08 4.48 0.41
rh rostral middle frontal 0.14 1.13 0.13 -2.09 2.39 1.00 0.62 0.90 0.68 -1.15 2.42 1.00
rh superior frontal -0.07 0.85 -0.08 -1.76 1.63 1.00 1.29 0.93 1.39 -0.49 3.18 1.00
lh rostral middle frontal 0.15 0.91 0.16 -1.64 1.95 1.00 0.74 0.96 0.76 -1.13 2.70 1.00
lh superior frontal 0.39 1.00 0.38 -1.60 2.39 1.00 2.00 1.09 1.83 -0.10 4.22 0.61 CI p Girls Value SE t CI p Value SE t Boys
For each ROI the regression coefficient (Value), Standard Error (SE), t-value (t), Confidence interval (CI) and p-value after Bonferroni correction are reported for girls and boys. The analyses were adjusted for baseline age, IQ and SES. The donating behavior groups were classified by percentage of donated money.
3.2 Effect of cortical thickness on donating behavior in boys
An ordinal logistic regression analysis was conducted to investigate the effect of cortical thickness on donating behavior two years later in boys. The analysis showed no significant effect of cortical thickness on donating behavior two years later in boys for all ROIs after a Bonferroni correction and adjusting for baseline age, IQ, and SES (Figure 5 and Table 3).
3.3 Effect of cortical thickness on donating behavior groups based on a percentile
As mentioned in table 2, the high donation behavior group had small sample size. To check whether the finding of no significant effect of cortical thickness on donating behavior in both boys and girls in all ROIs were not caused by the small sample size, an additional analysis was performed with rearranged donating behavior groups. Instead of classifying donating behavior by the percentage of donated money, the donating behavior was divided into three groups by percentile of 33.3%. This resulted in almost the same sample size within each donating behavior group. An ordinal logistic regression analysis between cortical thickness as the predictor and the donating behavior groups based on percentiles also showed no significant effect of cortical thickness on donating behavior two years later in both boys and girls for all ROIs after a Bonferroni correction and adjusting for baseline age, IQ and SES (Table 4).
Figure 5. Representation of relation between cortical thickness and donating behavior in boys
The individual effect of cortical thickness (x-axis) of each ROI on donating behavior (y-axis) for boys. Individuals were classified in high donating behavior (donated 80 – 100% of received money), middle donating behavior (donated 21 – 79% of received money) and low donating behavior (donated 0 – 21% of received money).
For each ROI the regression coefficient (Value), Standard Error (SE), t-value (t), Confidence interval (CI) and p-value after Bonferroni correction are reported for girls and boys. The analyses were adjusted for baseline age, IQ and SES. The donating behavior groups were classified by percentiles of 33.3%.
Lower (2.5%) Upper (97.5%) Lower (2.5%) Upper (97.5%) rh lateral orbitofrontal 0.21 0.59 0.36 -0.95 1.42 1.00 0.05 0.72 0.07 -1.37 1.49 1.00 rh pars orbitalis 0.05 0.40 0.13 -0.73 0.86 1.00 -0.40 0.66 -0.60 -1.71 0.89 1.00 rh precentral 0.95 0.82 1.16 -0.64 2.62 1.00 0.45 0.96 0.47 -1.44 2.36 1.00 rh postcentral 0.24 1.12 0.21 -1.99 2.45 1.00 1.59 1.22 1.30 -0.77 4.06 1.00 rh superior parietal 0.29 1.00 0.29 -1.67 2.32 1.00 0.64 0.97 0.66 -1.27 2.56 1.00
rh rostral middle frontal 0.58 0.97 0.60 -1.31 2.51 1.00 -0.13 0.83 -0.15 -1.77 1.50 1.00
rh superior frontal 0.77 0.72 1.07 -0.62 2.24 1.00 0.11 0.83 0.13 -1.53 1.75 1.00
lh rostral middle frontal 0.89 0.78 1.15 -0.62 2.48 1.00 0.34 0.88 0.39 -1.41 2.08 1.00
lh superior frontal 1.00 0.85 1.78 -0.65 2.73 1.00 0.93 0.99 0.94 -1.00 2.91 1.00 CI p Girls Boys Value SE t CI p Value SE t
4. DISCUSSION
While prosocial behavior is widely investigated, both in adults and children, limited studies investigated donating behavior (a specific construct of prosocial behavior) in middle childhood. Although studies observed neuroanatomical (cortical thickness) correlates of donating or prosocial behavior in middle childhood, whether the measure of cortical thickness influenced donating behavior or vice versa remained unclear. Therefore the present study investigated the effect of cortical thickness in nine brain regions associated with donating or prosocial behavior on charitable giving two years later and whether this effect differs between the sexes. The findings were not in line with the hypotheses. No significant effect was observed of cortical thickness on donating behavior two years later in both boys and girls. Therefore, no sex difference was observed in the relation between cortical thickness and donating behavior.
The first finding in the present study was that there was no effect observed between cortical thickness in regions that were associated with prosocial and donating behavior and donating behavior in middle childhood. This finding could suggest that donating behavior is more influenced directly by context or environment instead of cortical thickness as a neuroanatomical correlate. This suggestion is in line with the finding that seven-years-old children donate more money to a charity after probing by an adult experimenter, which suggests that donating behavior in children depends on the situation (van IJzendoorn et al., 2010). Furthermore, the suggestion that donating behavior is more influenced by context or environment is also in line with findings that parenting is positively related to prosocial behavior (Ferreira et al., 2016; Pastorelli et al., 2016). However, there should be mentioned that these findings were based on prosocial behavior. Therefore, it would be interesting in further research to investigate more the context and environmental influences on donating behavior.
The finding that there was no effect observed between cortical thickness and donating behavior in middle childhood in the present study does not imply this effect could not be observed at a later age state. The finding could suggest that in the present study, either donating behavior or cortical thickness or both were underdeveloped to observe an effect between cortical thickness and donating behavior. The children in the present study may not yet be able to think rationally about the need of the child in the charity video. This is in line with the finding that the cognitive process of reasoning about others’ needs, which is related to donating behavior, develops over time (Angerer et al., 2015; Ongley et al., 2014). Therefore, it could be that this cognitive process is underdeveloped to observe an effect between cortical thickness and donating behavior in middle childhood. Furthermore, besides the development of the cognitive process related to donating behavior, it also could be that the cortical thickness of the ROIs in the present study was underdeveloped to observe an effect between cortical thickness and donating behavior in middle childhood. Shaw et al. (2008) showed that most of the ROIs show significant development in thickening and thinning of the cortical thickness during middle childhood. It could be the cortex had to be thicker or had to be thinner to observe an effect between cortical thickness and donating behavior. It would be interesting to investigate in further research whether an effect of cortical thickness on donating behavior could be observed in late childhood or adolescence, where the cognitive process of reasoning about others’ need is more developed as well as the cortical thickness of regions related to this cognitive process or cortical thickness of the ROIs in the present study.
The second finding in the present study was that there was no observation of sex differences in the relation between cortical thickness on donating behavior in middle childhood. This finding is in contrast with previous research which observed sex differences in prosocial and donating behavior in middle childhood, adolescence and adults and a modulation effect of sex on the association between cortical thickness and prosocial behavior in middle childhood (Andreoni et al., 2003; Ferschmann et al., 2019; Thijssen et al., 2015). However, there should be mentioned that the observed sex differences in middle childhood and modulation effect of sex on the association between cortical thickness and prosocial behavior in middle childhood were based on a prosocial behavior measured with a parent report, which could cause sex stereotyping in the measure of prosocial behavior. Previous research in adults showed that sex differences in charitable giving were related to social norms (Croson et al., 2009). There was found that charitable giving positively was related to social norms in men, while charitable giving in females was not related to social norms. However, the relationship where social norms shape the donating behavior begins during middle childhood (House and Tomasello, 2018). Therefore, it could be that in middle childhood, the sex differences in the effect between cortical thickness and donating behavior cannot be observed, because the relation between social norms and donating behavior was underdeveloped yet.
However, the present study has to note some limitations. First, although the experimental design supported donating behavior with creating awareness of need using a charity video (Bekkers and Wiepking, 2011; Smith and Schwarz, 2012), 85.4% of the entire sample (including both boys and girls) donated less than or equal to half of the money they received. A possible explanation for the small number of children who donated more than half of the received money could be the present study sample was part of a larger longitudinal study (L-CID; see method). The donating measurement in the present study was a measurement during the third wave of the L-CID study, so the third time when the participants performed the donating task (although with different charity organization videos). This may produce “donor fatigue,” which could cause a lower donation (van Diepen et al., 2009) and could support the small number of children who donated more than half of the received money. Second, the present study performed region-wise analyses. The region-wise analysis in the present study was performed for ROIs based on associations between the cortical thickness of these ROIs and prosocial or donating behavior in previous research (Thijssen et al., 2015; Wildeboer et al., 2018). However, these two studies observed these associations after performing vertex-wise analyses. As a result, Thijssen et al. (2015) and Wildeboer et al. (2018) reported neuroanatomical correlates of prosocial or donating behavior as clusters, including parts of cortexes. The difference in analyses (region-wise versus vertex-wise) might cause the observation that there is no effect of cortical thickness on donating behavior in middle childhood in the present study. Because it could be that cortical thickness of brain clusters could affect donating behavior, but the average region thickness of the cortexes did not. However, the present study did region-wise analyses instead of a vertex-wise analysis because the region-wise analysis gives more statistical power. Third, the analysis in the present study performed a logistic regression. Performing a logistic regression could have as limitation choosing the right predictor of the model. Although previous studies observed an association between cortical thickness and donating/prosocial behavior, whether cortical thickness influenced the behavior or vice versa was not investigate. Therefore, the present study examined the influence of cortical thickness on donating behavior, but this effect was not observed. This could suggest that the present study did not choose the right predictor for the association between cortical thickness and donating or prosocial behavior. Therefore it would be interesting in further research to investigate whether donating behavior influenced the cortical thickness.
In conclusion, the present study observed no effect of cortical thickness in regions associated with prosocial and donating behavior on donating behavior in middle childhood. Furthermore, no sex differences were observed in the relation between cortical thickness on donating behavior in middle childhood. These findings could suggest that the cognitive process or cortical thickness related to donating behavior was underdeveloped in middle childhood to observe an effect of cortical thickness on donating behavior. Furthermore, the social norms related to charitable giving were underdeveloped yet to observe sex differences in the relation between cortical thickness and donating behavior in middle childhood. Finally, the findings in the present study could also suggest that donating behavior is more influenced by the environment instead of cortical thickness. While the present study did not observed that cortical thickness could influence donating behavior in middle childhood, further research could investigate whether donating behavior could influence cortical thickness. It is important to investigate this because when there is more known about the direction of the association between cortical thickness and prosocial behavior, this could be implemented in treatment processes for children, for example, with conduct disorder.
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