Thursday, August 17, 2006

Childhood Poverty and Neurocognitive Development

Does growing up in an empoverished home influence brain development? If so, how? A new article by Martha Farah and colleagues addresses these questions:
Farah MJ, Shera DM, Savage JH, Betancourt L, Giannetta JM, Brodsky NL, Malmud EK, Hurt H. (2006). Childhood poverty: Specific associations with neurocognitive development. Brain Res. Jul 29; [Epub ahead of print]

Growing up in poverty is associated with reduced cognitive achievement as measured by standardized intelligence tests, but little is known about the underlying neurocognitive systems responsible for this effect. We administered a battery of tasks designed to tax specific neurocognitive systems to healthy low and middle SES children screened for medical history and matched for age, gender and ethnicity. Higher SES was associated with better performance on the tasks, as expected, but the SES disparity was significantly nonuniform across neurocognitive systems. Pronounced differences were found in Left perisylvian/Language and Medial temporal/Memory systems, along with significant differences in Lateral/Prefrontal/Working memory and Anterior cingulate/Cognitive control and smaller, nonsignificant differences in Occipitotemporal/Pattern vision and Parietal/Spatial cognition.
The topic is mulitifaceted, controversial, and difficult to study without rasing a ruckus. With the mere mention of such a question,
How and why might a sociological construct, SES, be associated with brain function?
the media (and assorted pundits) raise the big red flags of genetic determinism and racial stratification (both pro and con). Fortunately, Farah and her colleagues are keenly aware of the Neuroethics involved in such a research enterprise, so they are not blindly stumbling into this line of work without an awareness of its social implications.

Some scientists plead ignorance of the controversy their work may inspire. Others are blatantly open about their xenophobic agendas. Among the worst offenders in the latter camp is J.P. Rushton, who published a paper that correlated measurements of hat size in military recruits with race, sex, and I.Q.
Rushton JP (1992). Cranial capacity related to sex, rank, and race in a stratified random sample of 6,325 U.S. military personnel. Intelligence 16:401-13.

The issue of whether human populations differ in brain size remains controversial. Cranial capacities were calculated from external head measurements reported for a stratified random sample of 6,325 U.S. Army personnel measured in 1988. After adjusting for the effects of stature and weight, and then, sex, rank, or race, the cranial capacity of men averaged 1,442 and women 1,332 cm3; that of officers averaged 1,393 and enlisted personnel 1,375 cm3; and that of Mongoloids averaged 1,416, Caucasoids 1,380, and Negroids 1,359 cm3.
It's kind of laughable that someone who has attracted so much media attention is the first to cry censorship...

And he's joined forces with that other paragon of complete genetic determinism, Arthur Jensen.
Rushton, J. P., & Jensen, A. R. (2005). Thirty years of research on race differences in cognitive ability. Psychology, Public Policy, and Law 11: 235-294.

Despite repeated claims to the contrary, there has been no narrowing of the 15- to 18-point average IQ difference between Blacks and Whites (1.1 standard deviations); the differences are as large today as they were when first measured nearly 100 years ago. They, and the concomitant difference in standard of living, level of education, and related phenomena, lie in factors that are largely heritable, not cultural. The IQ differences are attributable to differences in brain size more than to racism, stereotype threat, item selection on tests, and all the other suggestions given by the commentators. It is time to meet reality. It is time to stop committing the "moralistic fallacy" that good science must conform to approved outcomes.
No, this "science" conforms to outcomes approved by the Pioneer Fund. This non-profit group was founded by five American white male advocates of eugenics in 1937.

Hmm, what was the original topic of this post? Oh yeah, SES and brain development. Back to a more nuanced view (Farah et al., 2006).
Although SES is generally estimated by measuring parental education and occupational status, it encompasses far more than these simple indices, including associated differences in physical and mental health (Adler et al., 1994) and in physical and psychosocial aspects of the environment (Evans, 2004). Important psychosocial factors include the presence of both parents in the home and parental stress and depression. Physical factors include nutrition and exposure to pollutants. Any of these is, in principle, capable of influencing brain development and function. In addition, some of the variance in an individual's SES has been attributed to genetic factors (Lichenstein and Pederson, 1997), which could also be manifest in the brain.
The study used an extensive testing battery to assess different (purported) aspects of neurocognitive functioning. The authors relied on other neuroimaging studies to make an approximation between each cognitive test and a major brain region recruited to perform it. The participants were 30 low SES African American children and 30 middle SES African American children. The results are shown in Fig. 1 below.

There were significant differences between the groups on tests of language (left perisylvian), working memory (lateral prefrontal), cognitive control (anterior cingulate), and memory (medial temporal), but not for reward processing (ventromedial prefrontal), spatial cognition (parietal), or visual cognition (occipitotemporal). The authors state that
...cognitive ability is not depressed across the board among children of low SES. Rather, abilities that have been linked to specific neurocognitive systems are disproportionately affected.
Has anyone seen this experiment covered in the popular press? Of course not, because it admits that there are complicated and multifactorial reasons for such an outcome -- not amenable to an easy soundbyte!
The present study was not intended to identify the causes of the SES disparities found here. Given the complex nature of SES and its correlates, the list of possible causes is long, including: physical health factors such as prenatal care, nutrition and lead exposure; psychological factors such as stress, parental availability and childrearing practices; and genetic factors. Previous studies of SES disparities in cognitive development have either measured none or at most a few of these factors.
Furthermore,
A common misunderstanding regarding the neural bases of cognitive phenomena is that neural bases imply genetic bases.
SUMMARY from The Neurocritic: By merely recognizing the complexity of how SES may influence cognitive achievement, the authors have advanced the field of neurocognitive development.

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1 Comments:

At August 23, 2006 7:24 PM, Blogger Dan Dright said...

But how many mustard seeds can you fit in my empty cranium?????

 

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