A new study by a team of researchers from the University of Toronto (U of T) has identified the region of the brain’s hippocampus that links low income with decreased memory and language ability in children.
Previous research has shown that children from lower income families on average score lower in memory and language abilities than their higher income peers.
It is also known that a brain region that supports these abilities – called the hippocampus – is sensitive to the chronic stress that can be associated with lower socioeconomic status and that it is smaller in volume in children from lower income families.
Surprisingly, previous research had failed to show that the hippocampus underlies income-related gaps in cognition.
“What we found – and what makes this result novel – is that it’s the anterior hippocampus that is associated with differences in cognition related to income,” says Alexandra Decker, lead author of a study published today in Nature Communications.
Decker is a Ph.D. candidate in the Department of Psychology in the Faculty of Arts & Science at U of T. Her co-authors are professors from the department and include co-senior-author Amy Finn, Katherine Duncan and Donald J. Mabbott who is also with The Hospital for Sick Children (SickKids) in Toronto.
Decker and her colleagues arrived at their result by analyzing data previously gathered from a diverse sample of over 700 children, adolescents and young adults that included assessments of memory and vocabulary, as well as annual family income. They also studied MRI scans of participants.
Stresses and availability of resources associated with low socioeconomic status
The hippocampus is located in the brain’s temporal lobe. As part of the limbic system, it plays a vital role in learning and memory.
Previous research linked socioeconomic status and decreased levels of cognition but did not identify the hippocampus as the underlying cause, in part because the hippocampus was viewed as a single, homogeneous structure.
The result produced by Decker and her colleagues was based on growing evidence that the hippocampus comprises two distinct regions – the posterior and anterior.
According to Decker, “These regions develop differently and play different roles in cognition – and they have different sensitivities to stress.”
Although the data used in the study was limited to family income, Decker and her colleagues describe factors associated with socioeconomic status that could play a role in the effect—including stress and the availability of material and non-material resources.
“Parents from families with higher incomes are more able to take time off work and are less likely to be working multiple jobs,” says Decker.
“They’re also generally able to consistently afford enrollment in enriching programs and nutritious meals.”
What’s more, she says, children from lower socioeconomic backgrounds can experience a range of stressors. “For example, the stress borne by their parents about being able to make rent, pay bills and afford groceries.”
Insight for researchers, educators and policy makers
In addition, the researchers found that increases in income benefited brain development only up to a certain threshold.
“The relationship between income and the anterior hippocampus seems to be significant up to about an annual family income of about $75,000,” says Decker.
“There appear to be diminishing benefits at higher levels – which raises the question, why?
“More research needs to be done to answer this,” she says. “But it could be that at around $75,000, particular needs have been met.”
The researchers say the finding may be helpful to researchers, educators, and policy makers interested in promoting brain and cognitive health in children from families with lower incomes.
It may also provide insight into the types of cognitive processes that require more support in these children.
According to Finn, who is head of the Learning and Neural Development Lab at U of T, “These findings can help us understand how children from lower income backgrounds are uniquely disadvantaged compared to their peers from higher-income families on measures of cognitive ability.
“Understanding how these factors interact,” she says, “is central to designing means to boost cognitive performance in children from lower income backgrounds, with implications for social mobility, reducing achievement gaps and much more.”
“It raises the possibility,” adds Decker, “that we may eventually be able to prevent – at least to some extent – these negative effects on the brain. It suggests how we might be able to make a difference.”
Chronic, long-term poverty or low socioeconomic status (SES) is negatively associated with a variety of mental and physical adverse health outcomes.1
Disparities in the development of language processing are arguably among the most consistent, including vocabulary, phonological awareness, and syntax at many different stages of development,2-4 along with memory and cognitive control mental functions.5,6
In this review, we begin with an examination of candidate mechanisms by which low socioeconomic status influences brain development.
Recent research has demonstrated effects of poverty on brain functions in language and executive function areas in particular. We also discuss possible environmental and behavioral mediators of the effects of low SES on language development through pregnancy, the perinatal period, and parenting.
Next, we focus on two theoretical models that link poverty and adverse language development outcomes with consideration of related underlying brain physiology. First, we consider the family stress model, which posits that economic stress causes an increase in parental emotional distress and results in harsher, more authoritarian parenting practices and fewer opportunities for affection and nurturing.7
Second, we review the family investment model, which suggests that families in poverty, by necessity, focus time on the acquisition and assessment of basic needs.8
Finally, we conclude with discussions of how these models are helpful in understanding contributions of family dynamics and environment in the development of language processing and may inform the interpretation of research on biological mechanisms of poverty (Figure 1).
Most likely, poverty has adverse effects on language through both effects on parenting and increased stress, suggesting opportunities for early detection and treatment.
The literature reviewed suggests six neuroanatomical regions as central to the development of language (Figure 1).
The first three are language areas specific to auditory processing, visual processing, and word analysis and articulation, namely the perisylvian region of visual word form area (VWFA), and the anterior inferior frontal areas, respectively.
We postulate that these would be most affected by environmental influences such as parenting. In addition, areas associated with emotional processing, namely the amygdala and hippocampus, as well as PFC regions associated with cognitive control over emotion are central to self-regulation and its role in the development of language ability and may be especially vulnerable to the effects of chronic stress.
Parenting styles that include warmth, promotion of autonomy, and encouragement are predictive of strong language skills37 and better self-regulation,44 while controlling parenting strategies relate to the opposite.43
The ability to self-regulate in a learning situation is related to both SES and to parental language through the PFC.60
Research implications. There are several converging lines connecting poverty to language problems through stress, home language use, home literacy environment, and self-regulation, yet many questions remain unanswered.
Although poverty is related to language development through a number of pathways, in many studies, when controlling for other factors, poverty is still predictive of deviations from normative language development.
Among unanswered questions is that if poverty has a unique effect on language development, what is the mechanism through which poverty, controlling for other factors, influences language? One possible mechanism is the direct effects of stress on language development. Another mechanism involves perinatal and parenting factors (Figure 1).
Studies aimed at understanding the basic mechanisms of the perinatal period will help to understand the role of maternal stress in brain development supporting language.
The literature on environmental deprivation has demonstrated delays in left-right lateralization, development of the PFC,72 increased amygdala,70 and white matter disruption linking these regions.69
Taken together, these suggest a neuroanatomical pathway for decreased cognitive control, necessary for the higher order planning needed for language development17 and for understanding content.74
Although a growing number of studies have begun to explore the neurohormonal basis of parenting thoughts and actions in humans,75-77 it remains largely unknown how socioeconomic factors, either growing up in poverty or experiencing poverty later in life as an adult, affects the human parental brain—that is, specific brain circuitry that promote parental thoughts and behaviors.
Studies of this kind are still necessary to understand the risks associated with low SES and brain areas involved in caregiving motivation, which potentially simultaneously regulate approach and avoidance motivations to infant cues and are tied to the regulation stress response.78,79
These brain areas and caregiving behaviors are perhaps critical to creating the nurturing environment necessary for normal language development in early life.
A bright spot is that parental language use, independent of SES, is predictive of the development of normative language. This is an important area where there has been limited previous research.
Using the HOME interview, several researchers have found evidence that increases in the HLE are predictive of better language skills but studies that directly link HLE enhancement to neural function are lacking.
It is an open question whether there are both language deficits and perisylvian brain region deficits in low SES and whether they still occur after controlling for language ability in adults.
Finally, we present a caveat in this area of research given the focus on parenting and the home environment. Children from low SES backgrounds may have school circumstances that contribute to language development problems.
Such children often attend schools that have high student-to-teacher ratios, provide poor quality instruction, and lack access to academic resources (e.g., textbooks) that foster language development. Therefore, we acknowledge that the school environment deserves attention in models of lang
uage development and SES effects. Indeed, this may be an area of fruitful research in which certain improvements in school environments may compensate for SES-related problems.
Policy implications. For each $5,000 in extra income annually, vocabulary is raised an average of 2 points on a standard scale vocabulary measurement.3
Given that language deficits last into early adulthood24 and language delays increase the risk of long-term mental health outcomes,80 understanding the underlying neural mechanisms behind language delays in high poverty contexts has important public health implications.
Importantly the number of words spoken in the home can increase children’s vocabulary by 300 words at age two.80
This provides strong evidence that intervention in maternal-infant interactions, prior to age two, will have long-lasting effects on child language development and consequently on long-term health and welfare.
reference link : https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3659033/
More information: Alexandra L. Decker et al, Children’s family income is associated with cognitive function and volume of anterior not posterior hippocampus, Nature Communications (2020). DOI: 10.1038/s41467-020-17854-6