Not Race or Age but Their Interaction Predicts Pre-Adolescents’ Inhibitory Control

Background: African American pre-adolescents are at a higher risk of risky behaviors such as aggression, drug use, alcohol use, and subsequent poor outcomes compared to Caucasian pre-adolescents. All these high-risk behaviors are connected to low levels of Inhibitory Control (IC). Aim: We used the Adolescent Brain Cognitive Development (ABCD) data to compare Caucasian and African American pre-adolescents for the effect of age on pre-adolescents IC, a driver of high-risk behaviors. Methods: This cross-sectional analysis included 4,626 pre-adolescents between ages 9 and 10 from the ABCD study. Regression was used to analyze the data. The predictor variable was age measured in months. The main outcome was IC measured by a Stop-Signal Task (SST). Race was the effect modifier. Results: Overall, age was associated with IC. Race also showed a statistically significant interaction with age on pre-adolescents’ IC, indicating weaker effects of age on IC for African American than Caucasian pre-adolescents. Conclusion: Age-related changes in IC are more pronounced for Caucasian than African American pre-adolescents. To eliminate the racial gap in brain development between African American and Caucasian pre-adolescents, we should address structural and societal barriers that alter age-related development for racial minority pre-adolescents. Social and public policies, rather than health policies, are needed to address structural and societal barriers that hinder African American adolescents’ brain development. Interventions should add resources to the urban areas that many African American families live in so their children can have better age-related brain www.scholink.org/ojs/index.php/ct Children and Teenagers Vol. 3, No. 2, 2020 51 Published by SCHOLINK INC. development. Such changes would be essential given IC in pre-adolescents is a predictor of a wide range of behaviors.


Design and Settings
A secondary analysis was performed with a cross-sectional design. We used data from the Adolescent Brain Cognitive Development (ABCD) study (Alcohol Research: Current Reviews Editorial, 2018;Casey et al., 2018;Karcher, O'Brien, Kandala, & Barch, 2019;Lisdahl et al., 2018;Luciana et al., 2018). ABCD, a landmark study of brain development from pre-adolescence to emerging adults, is a unique study in the United States. Although details of the ABCD methods, measures, design, sample, and sampling are described elsewhere (Alcohol Research: Current Reviews Editorial, 2018;Auchter et al., 2018), here we briefly review them.

Participants and Sampling
In the ABCD, we only included pre-adolescents who were between the ages of 9 and 10 years. The ABCD pre-adolescents were enrolled from multiple cities across the states. Overall, pre-adolescents were recruited to the ABCD study from a total of 21 sites. The primary strategy for sampling in the www.scholink.org/ojs/index.php/ct Children and Teenagers Vol. 3, No. 2, 2020 54 Published by SCHOLINK INC.
ABCD study was recruiting from school systems (Garavan et al., 2018). In the current analysis, the sample was 4626 participants. Our analysis's inclusion criteria were having valid data on race, ethnicity, age, family SES, and task-based IC. Additionally, participants should only be African American or Caucasian.

Study Variables
The study variables included race, ethnicity, age, sex, family SES (parental education), family marital status, and task-based IC.
Inhibitory Control (IC). The ABCD study applied the Stop-signal Task (SST) to measure pre-adolescents' IC levels. The SST used in the ABCD applied two runs of 180 trials. Pre-adolescent subjects were shown images of a black arrow that were either pointing to right or left. These pictures were displayed on the monitor while the participant was in the scanner. Participants were asked to click the appropriate button that corresponds with the arrow direction as soon as they can see the image.
Participants were instructed that they should all use their dominant hand. From all 180 trials, 30 did not display either of the options, signaling the participant to inhibit their answers. These were randomly dispersed throughout the trial. IC in this study was defined as a successful inhibition of motor response.
Impulsivity was defined as answering with a wrong answer or an unsuccessful inhibition. For this study, IC was captured as the total number of "Stop" trials answered incorrectly (tfmri_sst_all_beh_incrs_nt).

Race.
Race, a self-identified variable, was a binary variable: 1 for African Americans and 0 for Caucasians (reference category).
Age. Age (months), calculated as the difference between birth and the time of enrollment to the study, measured in months, was reported by parents.
Marital status. Parental marital status, a dichotomous variable, was self-reported by the parents and was coded as married = 1 vs. other = 0.
Parental Educational Attainment. Participants were asked, "What is the highest grade or level of school you have completed or the highest degree you have received?" Responses ranged from 0 for never attended or kindergarten only to 21 for a doctoral degree. This variable, with a range between 1 and 21, was treated as an interval variable.

Data Analysis
The statistical package, SPSS, was applied for data analysis. Mean, Standard Deviation (SD), frequency, and relative frequency (%) were used to describe the study variables. We also performed an independent interaction terms. Model 2, another overall model, also added an interaction term between race and age (months). Model 3 and Model 4 were tested in Caucasian and African American pre-adolescents. In our models, age was used as the predictor, sex and family SES as the covariates, IC as the outcome, and race as the effect modifier. Unstandardized coefficient (b), SE, 95% CI, and p-value were reported for our model. p equal or less 0.05 was significant.

Ethics
The ABCD study protocol received Institutional Review Board (IRB) approval from several institutions, including but not limited to the University of California, San Diego (UCSD). All participating pre-adolescents provided assent. All participating parents signed informed consent (Auchter et al., 2018).
As we only performed a secondary analysis of fully de-identified data, our study did not require an IRB review (exempt from a full IRB review).

Descriptives
A total number of 4626 9-10 years old pre-adolescents were analyzed. Participants were mainly Caucasian (n = 3513; 75.5%), and only 24.1 (n=1113) were African Americans. Table 1 presents a summary of the descriptive statistics for the total sample and Caucasian and African American pre-adolescents.

Discussion
We found that IC correlates with age for Caucasian but not African American pre-adolescents. Due to the race by age interaction, age-related brain development in pre-adolescents may be delayed/hindered. This finding is an indicator of diminished age-related brain development of African American than Caucasian pre-adolescents. and tobacco use (Assari, Caldwell, et al., 2019). In other studies, MDRs were found for childhood trauma and stress (Assari, 2020a;Assari, 2020b  , and older adults (Assari & Lankarani, 2016a). Also, MDRs is not a pattern that can be exclusively seen for African Americans (Assari, Thomas, et al., 2018). In fact, same patterns are shown for Hispanic (Assari,  Several potential intuitive mechanisms may explain MDRs of age-related brain development in African American pre-adolescents. African American families and their pre-adolescents face many stressors and adversities, including financial stress, race-related stress, and environmental pollutants (Marshall et al., 2020). Unfortunately, these structural aspects impact the lives of African Americans across SES levels Assari, 2018h). African Americans have a low chance of upward social mobility (Chetty, Hendren, Kline, & Saez, 2014) and pay very high costs when they succeed (Hudson, Sacks, Irani, & Asher, 2020). For African American families, stress and discrimination are always high, regardless of SES Assari, Gibbons, & Simons, 2018a;Assari, Gibbons, & Simons, 2018b;. For African American families, low SES means living in poor areas, and high SES means high exposure to Caucasian families, which means very high levels of exposure to discrimination (Assari, Gibbons, et al., 2018a;Assari, Gibbons, et al., 2018b).
An example of structural causes of inequalities that generates MDRs in the USA is residential segregation. As a result of residential segregation, African American families live in resource-scarce environments full of stress and poverty. Due to residential segregation, African American pre-adolescents attend poor schools across SES levels . As a result, African American adolescents do not access many educational resources that stimulate brain development (Assari, 2019b;Assari & Caldwell, 2019b). However, poor education and schooling are only among the many differences in the lives of Caucasian and African American families (Jefferson et al., 2011).
It is important to note that MDRs reflect a particular class of disadvantage for racial minorities (Assari, 2017d;. While some disadvantages are due to lack of access to SES resources, MDRs of SES and age mean that African Americans experience poor outcomes across the same resources and assets (e.g., SES or age). Thus, research, practice, and policy should not merely focus on differential access to SES and different profiles of exposure to risk factors as causes of inequality. Policymakers and researchers should be aware that some observed inequalities are due to differential returns of age, SES, and other resources and assets. This type of disadvantage places African Americans at high risk across all levels of resources. It is also more difficult to undo MDRs-related inequalities than those that are due to poverty and low SES Assari, 2018h).
MDRs theory is a sociological rather than a biological explanation of health inequality. Among multilevel causes of MDRs, including economic, psychological, and societal mechanisms Assari, 2018h), racism and discrimination have a leading role. Racism operates across multiple institutions and social structures Assari, 2018h). If MDRs are due to racism, then a real solution to health disparities should also address MDRs-related inequalities. Such an approach requires increasing racial justice in the US. Age can only generate the same brain development when all racial groups have the same opportunity for brain development (Hudson et al., 2020;Hudson, Bullard et al., 2012;. African American families may stay in poor neighborhoods at all SES levels (Assari, Boyce, Caldwell, Bazargan, & Mincy, 2020). Caucasians, however, live in low-stress environments when they have high SES Assari, Preiser, & Kelly, 2018). Thus, even when they have similar SES, African American families' living conditions drastically differ from those of their Caucasian counterparts (Assari, 2018f;Assari & Bazargan, 2019b;Assari & Bazargan, 2019b;Assari, Gibbons et al., 2018a;Assari, Gibbons et al., 2018b;. Similarly, across all SES levels, African American adolescents spend time with high-risk peers Shanika Boyce, 2020).
However, high SES Caucasian adolescents have low-risk peers and family members Assari, Caldwell et al., 2019). The current study only documented MDRs of age-related brain development without digging into their societal and contextual causes. We argue that age shows a weaker effect on the brain development of children in less enriched environments.

Implications
The major implications of knowledge regarding MDRs-related inequalities are that it helps us rethink the structural causes of inequalities. Such knowledge is essential for finding the societal causes of racial disparities. It even helps us move our policies beyond equal access as a goal. In the presence of MDRs, equal access fails to generate equal outcomes. Due to MDRs of resources/assets such as SES and age, equality does not generate equity. To achieve equity, we need to equalize access to SES and the very societal conditions that surround African American children's development. The daily experiences of African American families should be improved. Thus, age-related brain development would be more equal across racial groups.

Limitations
All studies, particularly secondary analysis of some existing data, are limited in their methodology. As our study used a cross-sectional approach, we cannot make causal inferences. While IC does not cause age, age may impact IC. Still, longitudinal data are needed for establishing racial differences in the causal link between age and IC. More research is needed on MDRs of age as a source of brain development.
MDRs are commonly shown for SES indicators such as parental education, family income, and marital status; however, less is unknown about MDRs of age-related brain development. Finally, we only described the MDRs of age-related brain development without exploring the mechanisms of the observed MDRs. Future work is needed on the role of SES, trauma, stress, context, and family in explaining the observed MDRs of age-related brain development in African American adolescents.

Conclusion
For 9-10-year old American children, age is a predictor of IC for Caucasian children. For African American pre-adolescents, however, IC remains poor at all ages. That means the brain's age-related development that shapes IC differs for African American and Caucasian pre-adolescents. The results may help us understand why high-risk behaviors such as alcohol use, aggression, and early sexual debut are more common in African American than Caucasian children and adolescents.
Author Contributions: SA: data analysis, conceptualization, draft, revision, and approval, GA: revision, conceptualization, revision, and approval.  implemented the study and/or provided data but did not necessarily participate in analysis or writing of this report. This manuscript reflects the views of the authors and may not reflect the opinions or views of the NIH or ABCD consortium investigators. The ABCD data repository grows and changes over time.
The current paper used the Curated Annual Release 2.0, also defined in NDA Study 634 (doi:10.15154/1503209).