Using EEG to Assess the Impact of a Poverty Reduction Intervention On Brain Development
Post by Lani Cupo
The takeaway
While poverty can impact brain activity in children, this study shows predictable, unconditional, monthly money transfers to low-income homes can serve as a positive intervention in altering the brain activity of low-income children.
What's the science?
The first year of infants’ lives represents a period of great plasticity and sensitivity. In humans, it is difficult to assess the causality of variables such as income, as they often covary with other salient variables, like education or urbanicity. Previous evidence suggests early life poverty is associated with certain patterns in brain activity as measured with electroencephalograms (EEG). This week in PNAS, Troller-Renfree and colleagues seek to experimentally investigate whether financial intervention can alter brain activity associated with the development of cognitive skills.
How did they do it?
EEG provides researchers with noninvasive measures of two main variables: frequency (the waves of brain activity that occur at different rates) and power (the amount of activity at a specific frequency per region). From infancy to middle childhood, children show characteristic changes in EEG signals, with decreasing power in low frequency bands (slow oscillations called theta) and increasing power in high frequency bands (higher oscillations, alpha, beta, and gamma). Differences in this changing pattern are associated with poorer cognitive outcomes, often correlated with poverty during the first years of life. To assess whether poverty reduction strategies could alter brain activity in infants, 1000 low-income women from 4 urban areas in the United States were randomized to receive a gift of either $20 per month (low-cash gift) or $333 (high-cash gift) per month, to be used as they chose. When the infants were one-year old and the mothers had received the gifts for one year, surveys and EEG recordings were completed in 435 infants. The authors examined both absolute and relative power, where absolute power refers to the amount of power measured at a specific frequency band and relative power refers to the fraction of absolute power over total power. For example, absolute power would reflect the power measured in the low-frequency theta band, and the relative power would reflect the theta power over the combined alpha, beta, and gamma power.
What did they find?
Compared to the low-cash group, children in the high-cash group had higher absolute power in the mid-high frequency ranges (alpha, beta, and gamma), as hypothesized. Higher power in mid-to-high-frequency bands has been associated with better cognitive and language outcomes. Of the three frequency ranges, the greatest effect size was observed in the beta range, indicating it was the most impacted. Of note, beta frequencies have been associated with eye movement artifacts, and potentially with concentrated activity.
The same patterns were reflected in relative power, although the effects were smaller. The high-cash group showed increased frontal beta and gamma power, as well as more central beta power, indicating regions consistent with previous work linking income, brain activity, and cognitive outcomes. There was no impact on theta-power, contrary to hypotheses. Previous work in children indicates high theta power is associated with poorer behavioral outcomes, and the authors expected to see reduced theta power in the high-cash group.
What's the impact?
This study is the first to report a causal relationship between income level and brain activity in young children by implementing a poverty-reduction intervention for low-income mothers. They found an unconditional payment of $333 per month was sufficient to increase mid-high frequency power in EEG recordings at age 1. This work provides important experimental evidence that could impact public policy to reduce inequality and ensure better outcomes for low-income children.
