Diversity in the Biology of the Brain
Diagnosing dementia and other cognitive disorders among racially and ethnically diverse populations can be challenging. Many of the tests used for such diagnoses have intrinsic cultural and linguistic bias. Consequently, scientists have yet to determine differences in the prevalence, incidence, and etiology of (factors contributing to) dementia among various racial and ethnic groups.
Faced with the challenge of determining how cognitive problems manifest differently on a biological level among racial groups, a team of researchers from the University of California at Davis and Berkley turned their attention to structural brain imaging (MRI). As they describe, “structural brain imaging is commonly used to study the biology of normal aging and cognitive impairment and may therefore serve to explore potential biological differences of cognitive impairment among racially and ethnically diverse individuals.” Specifically, researchers studied how the relationship between brain structure and dementia are similar and different among African Americans, Hispanics, and Caucasians. Investigators used this information to determine the accuracy (or cultural sensitivity) of their methods for clinically diagnosing cognitive impairment. Findings from this research are in the article, “Brain Behavior Relationships Among African Americans, Whites, and Hispanics,” published in the October-December 2008 issue of Alzheimer Disease & Associated Disorders.
The team of researchers first clinically diagnosed each participant as having normal cognition, mild cognitive impairment, or dementia using traditional methods that included physical and psychological exams. Following the clinical diagnosis, investigators (blinded of subjects’ age, sex, ethnicity, race, and diagnostic category) used MRI images to determine the biological differences and similarities in the brains of the participants, looking for any patterns.
“What we learned is that we can bring in a very diverse group of individuals, African American, Hispanic, and White, ranging in education from none to 20 years, [clinically] diagnose them, and show that relationship between the clinical diagnosis and brain variables are the same among all individuals,” explains lead author, Charles DeCarli, M.D. All dementia participants had loss of brain substance and increase in white matter abnormalities associated with mild cognitive impairment and dementia.
“But then there was a twist, based on race. The Hispanic participants had a smaller head size and larger proportion of regional brain volume and why is that? It is probably a mixture of genetic and environmental influences. On one hand we can clinically evaluate diverse people using the same methods. But by looking at diverse people, we can see interesting and potentially informative biological influences that might tell us about disease pathophysiology,” says DeCarli.
This study demonstrates the benefit of having a diverse participant pool. When research involves a homogeneous group, the findings may not apply to or benefit other populations. According to the investigators in this study, their findings about cognitive impairment are more likely to help a broader audience because they are based on research with diverse participants. Recruiting underrepresented populations is not easy—it is a continual challenge for investigators in all fields, not just aging. But when achieved, the results are notable.