Racism May Weaken the Brain-Behavior Association among African American Children: The Case of Amygdala Volume-Emotion Regulation Link

Assari S; Najand B; Mays VM

Research Article

J Pediatri Endocrinol. 2022; 7(1): 1049.

Racism May Weaken the Brain-Behavior Association among African American Children: The Case of Amygdala Volume-Emotion Regulation Link

Assari S^1,2,3*, Najand B¹ and Mays VM^4,5,6

¹Marginalization Related Diminished Returns Research Center, Charles R. Drew University of Medicine and Science, Los Angeles, CA, USA

²Department of Family Medicine, Charles R. Drew University of Medicine and Science, Los Angeles, CA, USA

³Department of Urban Public Health, Charles R. Drew University of Medicine and Science, Los Angeles, CA, USA

⁴BRITE Center for Science, Research & Policy, UCLA, Los Angeles, CA, USA

⁵Department of Health Policy, Fielding School of Public Health, UCLA, Los Angeles, CA, USA

⁶Department of Psychology, UCLA, Los Angeles, CA, USA

*Corresponding author: Shervin Assari, Marginalization Related Diminished Returns Research Center, Charles R. Drew University of Medicine and Science, Los Angeles, CA, USA

Received: January 10, 2022; Accepted: February 28, 2022; Published: March 07, 2022

Abstract

Introduction: The amygdala has a central core role in regulating emotions. However, less is known about the racial/ethnic variation in the relevance of amygdala volume for emotion regulation of US children. According to the Minorities’ Diminished Returns (MDRs) phenomenon, due to racism, segregation, and social stratification (rather than innate differences due to genetics), some of the individual-level individual social determinants, could lose some of their relevance for African American (in comparison to White) children.

Purpose: Conceptualizing race as a social factor that reflects structural racism and discrimination and building on the MDRs framework, we explored racial variation in the magnitude of the association between amygdala volume and emotion regulation/impulsivity of US children.

Methods: For this cross-sectional study, we used baseline data which included behavioral, social, and structural magnetic resonance imaging (MRI) data of 6030 US children ages 9-10. Data came from the Adolescent Brain Cognitive Development (ABCD) study. The primary outcomes were positive and negative urgency. These were measured using Urgency, Premeditation (lack of), Perseverance (lack of), Sensation Seeking, Positive Urgency, and Impulsive Behavior Scale (UPPS-SS) UPPS-SS. The independent variables were right and left amygdala volume. The covariates were age, sex, parental education, household income, parental marital status, neighborhood socioeconomic status, and ethnicity. Race was the moderator.

Results: Children with larger amygdala volumes had lower positive and negative urgency. The correlations between amygdala volume and positive and negative urgency were modified by race. For White children, children had better emotion regulation when they had a large amygdala. For African American children, positive and negative urgency did not show an association with amygdala size.

Conclusions: The results can be explained by the Minorities’ Diminished Returns (MDRs) hypothesis. In line with MDRs and as a result of structural and interpersonal inequalities, such as school segregation, the amygdala-emotion regulation seen for White children does not replicate for African American children. For White children, however, in the absence of higher-level social determinants, amygdala size correlates with emotion regulation. The brainbehavior link is weaker for African American children whose lives are less predictable and affected by experiences of racial discrimination. Unequal effects of equal resources across racial groups are due to racism and discrimination, not biological innate differences such as genetics.

Keywords: Amygdala; Limbic System; Children; MRI; Population groups; Emotion Regulation; Impulse Control; Inhibitory Control

Introduction

The right and left amygdala, almond-like structures [1], located deep in the brain’s medial temporal lobe of each hemisphere, are core elements of the limbic system and play a major role in emotion processing and regulation [2-9]. For humans and animals, the right and left amygdala modulate all reactions to emotionally charged events and sensory input [2]. The role of the amygdala in regulating human emotions and behaviors is well-described [10-13]. This subcortical brain structure processes emotionally charged, rewarding, and or threatening environmental inputs and stimuli [14] and has a major role in emotions [1]. Although the amygdala is best known for its role in processing fear and threat, it also has a role in emotion regulation, inhibitory control, and decision making [15]. While changes of the amygdala are best known in anxiety disorders such as general anxiety disorder (GAD), post-traumatic stress disorder (PTSD) [4-6,16], phobias and panic disorder (PD) [17], altered amygdala function and size is shown for other disorders and problem such as autism, schizophrenia [18,19], aggression [20,21] and depression [22].

The amygdala size- emotion regulation is well described in the neuroscience literature [23]. As a result, youth and adults with a smaller amygdala are at an increased risk of mood disorders [24] such as bipolar disorder [25] and depression [22,26]. In most disorders mentioned above, the amygdala is small but hyperactive [24,27]. It is, however, unknown if behavioral correlation of amygdala size differs across population sub-groups, particularly those racialized as White and African American [28].

Race, which can closely overlap with socioeconomic status (SES) and chronic stress, can serve as a proxy of exposure to racism and other environmental factors that may impact various brain structures including the amygdala [29-32]. Race impacts amygdala and other brain structures, because racial/ethnic minority populations are chronically exposed to various forms of discrimination, stress, and economic disadvantages [33]. Thus; some of the race effects on the brain can be a function of the experiences associated with SES, particularly at the lower end especially in the case of poverty like experiences [33]. However, the SES effects on brain may also vary by race. Some studies have shown that SES effects on shaping some brain structures may be more robust for low SES children [33]. Due to racism, discrimination, and segregation, however, racial minority groups may not show the effects of SES on brain [34]. This is recently described as racism-related diminished returns of SES on children’s brain development [35,36].

Minorities’ Diminished Returns (MDRs) have been shown?? To have weaker SES effects for African Americans than White individuals. These MDRs emerge because high SES African American families have lower household income and wealth and experience higher levels of stress and discrimination [37-41]. As a result of residential segregation, moderate to high SES African American children can remain with high-risk peers [42] and in high-risk schools [43] and neighborhoods [44]. Similarly, moderate to high SES African American children still experience high levels of chronic stress [44-46], which have been shown to hinder their healthy brain development [8,47-49]. Similar MDRs are shown for the effects of SES on trauma [46], ADHD [50], suicide [51], depression [52], anxiety [53], aggression [54], tobacco use [54-56], impulsivity [57], school bonding [58], school performance [59], and inhibitory control [60]. All these SES effects are stronger in White than African American youth. These African American-White differences in the SES effects (i.e., MDRs) are frequently replicated [41,61-63], suggesting that weakened effect of SES in African American than White children is a robust phenomenon [61]. In this view, family-level SES have smaller than expected effects on shaping African American children’s brain development [50,63-68]. That means it is related to the social structural -level barriers (e.g., segregation) and interpersonal stressors (e.g., discrimination) that SES resources lose some of their effects for African Americans when compared to Whites [61]. For example, due to experiences like labor market discrimination, segregation, and racism, experiences of high-SES and low-SES African American families are more similar [61] than among high-SES and low-SES White families [37]. This is partly because SES can be more protective for populations which do not face chronic forms of race-based discrimination (e.g., American Whites) [38,69].

In the Adolescent Brain Cognitive Development (ABCD) study [70-73], family SES increased the amygdala size for White children but not African American children [34]. Similar patterns were observed for the thalamus [74], hippocampus [75], cerebral cortex [76,77], and cerebellum [78]. In another paper, SES showed stronger effects on brain structure and function in White people than African American people [79].

MDRs, however, are not limited to SES. Not only economic but also non-economic resources and assets lose some of their beneficial or protective effects in African Americans than Whites [63,80,81]. For example, age, emotion regulation, self-efficacy, and coping show larger positive health consequences for Whites than African Americans [82- 89]. In the same manner that SES indicators have weaker effects on positive health outcomes for African Americans than Whites. As a function of racism and discrimination, brain mechanisms and how brain structures function under these conditions may have weaker effects on behavioral and physical health outcomes for African Americans than White communities [38,90].

Aims

Employing data from the ABCD study and the MDRs framework, we used the behavioral [54] and brain imaging data [34] to investigate the differential effect of amygdala size on positive/negative urgency of 9-10 years old American children. Our first hypothesis was an inverse association between amygdala size and positive/negative urgency of the children. Our second hypothesis was a weaker association between amygdala size and positive/negative urgency as a proxy of emotion regulation and impulsivity for African American than White children. In other words, we expect high levels of positive/ negative urgency for African American children regardless of the child’s amygdala size. For White children, however, our prediction is an inverse association between amygdala size and positive/negative urgency (as a proxy of emotion regulation and impulsivity).

Methods

Design and settings

This was a secondary analysis of wave 1 of the Adolescent Brain Cognitive Development (ABCD) study [70-73]. The ABCD is national existing data of brain imaging and child development. The ABCD data was borrowed from the NDA website. The ABCD is a landmark brain development study of United States youth. Detailed information on the ABCD methods, sampling, sample, measures, and imaging techniques are available here [70-73,91,92].

Participants and sampling

The ABCD participants were 9-10 children, who were between ages 9 and 11 years. Children in the ABCD study were recruited from multiple cities across multiple states. Overall, participants were enrolled from 21 different sites. The primary source of recruitment for the ABCD sample was US school systems. The sampling protocol of the ABCD study is described in detail here [70]. In the specific analysis, our sample was composed of a total number of 6030 9-10-year-old participants who were either White or African American. Our analysis’s eligibility included valid data on race, ethnicity, demographics, parental education, parental marital status, amygdala volume, and positive and negative urgency.

Study variables

Amygdala volume: The independent variables were the right and the left amygdala volume (mm3), measured by structural MRI at rest, as described here [93].

Moderator

Race: Race was self-identified by the parent. Race was a dichotomous variable: African American and White (reference category).

Outcomes: Outcomes were positive and negative urgency. These were measured using the Urgency, Premeditation (lack of), Perseverance (lack of), Sensation Seeking, Positive Urgency, Impulsive Behavior Scale (UPPS-SS) UPPS-SS. Positive and negative urgency are correlated constructs that reflect two inter-related aspects of impulsivity. Positive urgency is the inability to wait and postpone reward. Negative urgency is the inability to tolerate negative input. In this study, positive urgency was treated as a continuous measure, with a higher score indicating higher positive urgency traits (higher impulsivity). The UPPS-SS is a valid and reliable measure [94-100]. These constructs have shown reliability and validity in past research [101-103].

Age, sex, ethnicity, household income, parental education, neighborhood SES, and parental marital status were the confounding variables. Ethnicity was measured by the self-identification of the parents. Ethnicity was a dichotomous variable and coded 1 for Latino and 0 for non-Latino (reference category) families. Parents reported children’s age which was calculated as months passed since birth. Sex of the child was a dichotomous variable that was coded 0 for males and 1 for females. Parental educational attainment was an ordinal variable: less than high school (reference category), high school, college, graduate + school. Parental marital status was also a dichotomous variable, self-reported by the parent interviewed, and coded 1 vs. 0 for married and unmarried families respectively. Parental education was a continuous measure reflecting years of schooling. Household income was a continuous measure ranging from 1 to 10, with a higher score indicating higher SES. We also used Area Deprivation Index (Neighborhood disorder) [104] as the measure of social context.

Data analysis

We used SS 25.0 for data analysis. The primary outcomes were positive and negative urgency. The independent variables were right and left amygdala volume. Covariates were age, sex, parental marital status, parental education, Area Deprivation Index (Neighborhood disorder) [104], and ethnicity. Model 1 tested the additive effects of amygdala size and race, with the same covariates, without interaction terms. Model 2 tested the interaction between amygdala size and race with all covariates. We ran identical models for the right and left amygdala and positive and negative urgency. Before running our models, we checked a wide range of assumptions, including normal distribution of our outcomes, lack of collinearity between predictors and covariates, and the distribution of errors for our models.

Ethical aspect

Our secondary analysis was found by the Charles R Drew University of Medicine and Science (CDU) Institutional Review Board (IRB) to be exempt from a full IRB review. However, the original ABCD study underwent an Institutional Review Board (IRB) in several institutions, including but not limited to the University of California, San Diego (UCSD). The IRB in multiple institutions approved the ABCD study protocol, and all of the children provided assent, and the parents signed consent.

Results

Sample descriptive data

Table 1 shows descriptive data overall. This study included 6030 children who were 9-10 year of age. From this number, 75.6% were White, and 24.4% were African American. Table 1 also compared study variables by race. African American and White children did not differ in age or sex, but they differed in Hispanic ethnicity, positive and negative urgency, SES, and right and left amygdala volume (size).

Table 1: Descriptive statistics in the pooled sample by race.




  
    
    All
    African American
    White
  
  
    n
    %
    n
    %
    n
    %
  
  
    Race
     
     
     
     
     
     
  
  
    White
    4558
    75.6
        -
        -
    4558
        100
  
  
    AA
    1472
    24.4
    1472
        100
        -
        -
  
  
    Ethnicity
     
     
     
     
     
     
  
  
    Non
    5044
    83.6
    1346
    91.4
    3698
    81.1
  
  
    Latino*
    986
    16.4
    126
    8.6
    860
    18.9
  
  
    Sex
     
     
     
     
     
     
  
  
    Female
    2633
    43.7
    684
    46.5
    1949
    42.8
  
  
    Male
    3397
    56.3
    788
    53.5
    2609
    57.2
  
  
    Puberty*
     
     
     
     
     
     
  
  
    Pre
    1634
    27.1
    280
    19
    1354
    29.7
  
  
    None
    4396
    72.9
    1192
    81
    3204
    70.3
  
  
    Married Family*
     
     
     
     
     
     
  
  
    No
    1946
    32.3
    974
    66.2
    972
    21.3
  
  
    Yes
    4084
    67.7
    498
    33.8
    3586
    78.7
  
  
     
    Mean
    SD
    Mean
    SD
    Mean
    SD
  
  
    Age
    9.4951
    0.50843
    9.486
    0.5137
    9.498
    0.50674
  
  
    Residential history derived -    Area Deprivation Index 

      (based on Kind et al., Annals    of Internal Medicine, 2014)*
    93.56
    24.408
    104.86
    21.825
    89.9
    24.078
  
  
    Parental Education*
    16.7706
    2.56602
    15.3988
    2.57596
    17.2137
    2.40108
  
  
    Financial Difficulty*
    0.0687
    0.16051
    0.1446
    0.21859
    0.0442
    0.1273
  
  
    Amygdala Volume (Right)/1000*
    1.6179
    0.2266
    1.5499
    0.21269
    1.6399
    0.22661
  
  
    Amygdala Volume (Left)/1000*
    1.5757
    0.23124
    1.4955
    0.21234
    1.6016
    0.23116
  
  
    Positive Urgency*
    7.98
    2.944
    8.57
    3.207
    7.78
    2.828
  
  
    Negative Urgency*
    8.52
    2.645
    8.81
    2.859
    8.42
    2.565
  
  
    *p<0.001 for comparison of African American    and White children.



Table 1: Descriptive statistics in the pooled sample by race.

Regressions

Positive urgency: As shown by Table 2, the right and left amygdala size affected positive urgency when all confounders were controlled. However, the protective effect of children’s right amygdala size on positive urgency was smaller in African Americans than in White children.

Table 2: Association between amygdala volume and positive urgency.




  
    
    Model 1
    Model 2
  
  
    b
    SE
    Beta
    95%CI
    p
    b
    SE
    Beta
    95%CI
    p
  
  
    Right
     
     
     
     
     
     
     
     
     
     
     
     
  
  
    Race (AA)
    0.336
    0.102
    0.049
    0.137
    0.536
    0.001
    -1.241
    0.64
    -0.181
    -2.496
    0.014
    0.053
  
  
    Ethnicity (Hispanic)
    -0.081
    0.105
    -0.01
    -0.288
    0.125
    0.439
    -0.089
    0.105
    -0.011
    -0.295
    0.118
    0.399
  
  
    Age (Yr)
    -0.148
    0.074
    -0.025
    -0.292
    -0.003
    0.046
    -0.145
    0.074
    -0.025
    -0.29
    -0.001
    0.049
  
  
    Male
    0.58
    0.08
    0.098
    0.423
    0.736
    0
    0.579
    0.08
    0.098
    0.423
    0.735
    0
  
  
    Puberty
    0.349
    0.085
    0.053
    0.182
    0.516
    0
    0.351
    0.085
    0.053
    0.185
    0.518
    0
  
  
    Married
    -0.185
    0.092
    -0.029
    -0.365
    -0.005
    0.044
    -0.189
    0.092
    -0.03
    -0.37
    -0.009
    0.039
  
  
    Area Deprivation Index (Kind    2014)
    0.004
    0.002
    0.029
    0
    0.007
    0.032
    0.004
    0.002
    0.03
    0
    0.007
    0.029
  
  
    Parental Education
    -0.078
    0.017
    -0.068
    -0.111
    -0.045
    0
    -0.077
    0.017
    -0.067
    -0.11
    -0.044
    0
  
  
    Financial Difficulty
    0.996
    0.251
    0.054
    0.505
    1.487
    0
    1.004
    0.251
    0.055
    0.513
    1.495
    0
  
  
    Right Amygdala Volume/1000
    -0.467
    0.177
    -0.036
    -0.815
    -0.12
    0.008
    -0.689
    0.198
    -0.053
    -1.078
    -0.3
    0.001
  
  
    Right Amygdala Volume/1000 x    Race (AA)
     
     
     
     
     
     
    1.003
    0.402
    0.23
    0.215
    1.79
    0.013
  
  
    Left
     
     
     
     
     
     
     
     
     
     
     
     
  
  
    Race (AA)
    0.323
    0.102
    0.047
    0.123
    0.523
    0.002
    -0.288
    0.62
    -0.042
    -1.503
    0.927
    0.642
  
  
    Ethnicity (Hispanic)
    -0.091
    0.105
    -0.011
    -0.297
    0.116
    0.389
    -0.096
    0.105
    -0.012
    -0.302
    0.111
    0.364
  
  
    Age (Yr)
    -0.14
    0.074
    -0.024
    -0.285
    0.004
    0.057
    -0.141
    0.074
    -0.024
    -0.286
    0.004
    0.057
  
  
    Male
    0.589
    0.079
    0.099
    0.433
    0.745
    0
    0.589
    0.079
    0.099
    0.433
    0.745
    0
  
  
    Puberty
    0.35
    0.085
    0.053
    0.184
    0.517
    0
    0.351
    0.085
    0.053
    0.184
    0.518
    0
  
  
    Married
    -0.184
    0.092
    -0.029
    -0.364
    -0.004
    0.046
    -0.186
    0.092
    -0.03
    -0.366
    -0.006
    0.043
  
  
    Area Deprivation Index (Kind    2014)
    0.003
    0.002
    0.029
    0
    0.007
    0.036
    0.003
    0.002
    0.029
    0
    0.007
    0.034
  
  
    Parental Education
    -0.078
    0.017
    -0.068
    -0.111
    -0.045
    0
    -0.078
    0.017
    -0.068
    -0.111
    -0.045
    0
  
  
    Financial Difficulty
    0.988
    0.251
    0.054
    0.497
    1.479
    0
    0.995
    0.251
    0.054
    0.504
    1.487
    0
  
  
    Right Amygdala Volume/1000
    -0.54
    0.174
    -0.042
    -0.882
    -0.198
    0.002
    -0.625
    0.194
    -0.049
    -1.006
    -0.244
    0.001
  
  
    Right Amygdala Volume/1000 x    Race (AA)
     
     
     
     
     
     
    0.401

    0.401
    0.089
    -0.385
    1.187
    0.317



Table 2: Association between amygdala volume and positive urgency.

Negative urgency: As shown by Table 3, the right and left amygdala size affected negative urgency when all confounders were controlled. However, the protective effects of children’s right and left amygdala size on negative urgency were smaller in African American children than in White children.

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Citation: Assari S, Najand B and Mays VM. Racism May Weaken the Brain-Behavior Association among African American Children: The Case of Amygdala Volume-Emotion Regulation Link. J Pediatri Endocrinol. 2022; 7(1): 1049.

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	Model 1						Model 2
	b	SE	Beta	95%CI		p	b	SE	Beta	95%CI		P
Right
Race (AA)	0.164	0.092	0.027	-0.017	0.344	0.076	-1.731	0.579	-0.281	-2.866	-0.597	0.003
Ethnicity (Hispanic)	-0.32	0.095	-0.045	-0.506	-0.133	0.001	-0.328	0.095	-0.046	-0.515	-0.142	0.001
Age (Yr)	-0.077	0.067	-0.015	-0.207	0.054	0.252	-0.074	0.067	-0.014	-0.205	0.057	0.268
Male	0.601	0.072	0.113	0.46	0.742	<0.001	0.6	0.072	0.113	0.459	0.741	<0.001
Puberty	0.466	0.077	0.078	0.316	0.617	<0.001	0.469	0.077	0.079	0.318	0.62	<0.001
Married	-0.028	0.083	-0.005	-0.191	0.135	0.735	-0.033	0.083	-0.006	-0.196	0.129	0.687
Area Deprivation Index (Kind 2014)	-0.002	0.001	-0.018	-0.005	0.001	0.188	-0.002	0.001	-0.017	-0.005	0.001	0.202
Parental Education	-0.049	0.015	-0.048	-0.079	-0.019	0.001	-0.049	0.015	-0.047	-0.079	-0.019	0.001
Financial Difficulty	0.595	0.227	0.036	0.151	1.039	0.009	0.605	0.226	0.037	0.161	1.049	0.008
Right Amygdala Volume/1000	-0.321	0.16	-0.028	-0.635	-0.007	0.045	-0.587	0.179	-0.05	-0.939	-0.236	0.001
Right Amygdala Volume/1000 x Race (AA)							1.204	0.363	0.307	0.493	1.916	0.001
Left
Race (AA)	0.159	0.092	0.026	-0.023	0.34	0.086	-1.042	0.56	-0.169	-2.14	0.056	0.063
Ethnicity (Hispanic)	-0.324	0.095	-0.045	-0.511	-0.137	0.001	-0.333	0.095	-0.047	-0.52	-0.146	<0.001
Age (Yr)	-0.073	0.067	-0.014	-0.204	0.058	0.274	-0.074	0.067	-0.014	-0.205	0.057	0.271
Male	0.599	0.072	0.112	0.459	0.74	<0.001	0.599	0.072	0.112	0.458	0.74	<0.001
Puberty	0.467	0.077	0.079	0.316	0.618	<0.001	0.468	0.077	0.079	0.318	0.619	<0.001
Married	-0.028	0.083	-0.005	-0.191	0.135	0.737	-0.032	0.083	-0.006	-0.195	0.131	0.699
Area Deprivation Index (Kind 2014)	-0.002	0.001	-0.018	-0.005	0.001	0.179	-0.002	0.001	-0.018	-0.005	0.001	0.192
Parental Education	-0.05	0.015	-0.048	-0.079	-0.02	0.001	-0.049	0.015	-0.048	-0.079	-0.019	0.001
Financial Difficulty	0.593	0.227	0.036	0.149	1.037	0.009	0.608	0.227	0.037	0.163	1.052	0.007
Right Amygdala Volume/1000	-0.316	0.158	-0.028	-0.625	-0.007	0.045	-0.484	0.176	-0.042	-0.829	-0.14	0.006
Right Amygdala Volume/1000 x Race (AA)							0.788	0.363	0.194	0.077	1.498	0.03

Racism May Weaken the Brain-Behavior Association among African American Children: The Case of Amygdala Volume-Emotion Regulation Link

Abstract

Introduction

Aims

Methods

Design and settings

Participants and sampling

Study variables

Moderator

Data analysis

Ethical aspect

Results

Sample descriptive data

Regressions

Discussion

Limitations

Implications

Conclusion

Declaration

References