Does brain structure truly reflect intelligence?

IQ is one of the most studied characteristics in brain imaging research. However, according to a recent study published in Science, in the child population, the relationship between IQ and brain structure and function is actually weaker than that of socioeconomic status.

The research results show that once the factor of socioeconomic status is controlled, the seemingly existing association between IQ and brain differences basically disappears. The researchers said that this finding highlights the importance of including the factor of socioeconomic status when analyzing brain imaging datasets.

"If you don't properly consider socioeconomic status in a brain imaging experiment," said Nico Dosenbach, a professor of neurology at Washington University in St. Louis and one of the study's authors, "you're going to deceive yourself."

Dosenbach and his colleagues analyzed the MRI scan data and behavioral data of approximately 12,000 children aged 9 to 10 in the Adolescent Brain Cognitive Development (ABCD) Study, seeking the correlation between brain structure and function indicators and 649 psychological, health, social, and environmental factors. The results showed that socioeconomic variables - such as family income and the place where the child lives - were most significantly associated with functional connectivity and cortical thickness.

The study found that socioeconomic differences can explain 16% of the variation in functional connectivity among participants. Russ Poldrack, a professor of psychology at Stanford University who was not involved in the study, said that this is "one of the largest effects observed in such studies." Socioeconomic status can also explain approximately 13% of the variation in cortical thickness. Sleep and screen time are also highly correlated with these brain characteristics, although the strength of the association is still weaker than that of socioeconomic factors.

Poldrack said that these findings have important implications for how researchers will conduct and interpret related studies in the future. "We must think very deeply about the possible confounding factors. We can't just calculate correlations and then assume they mean what we think they do."

According to a study published by Dosenbach's team in 2022, psychological performance indicators such as IQ and working memory are more strongly associated with brain differences than mental health indicators. However, Scott Marek, an assistant professor of radiology at the School of Medicine at Washington University in St. Louis and one of the authors of this study, said that when the research team included socioeconomic status in the analysis, the association they previously found between IQ and brain organizational structure disappeared.

In this new study, the research team trained a machine learning model to predict IQ based on brain scan data. When the model was trained using the complete ABCD dataset, it could accurately predict IQ; but when the model was trained using only the data of children with high socioeconomic status, the predictive ability disappeared. The study showed that a model trained using only the data of children with lower socioeconomic status was as good at predicting IQ as a model trained using the entire sample.

Even though these models were initially only trained to predict IQ based on brain scans, their ability to predict children's socioeconomic status was still better than their ability to predict IQ. Marek said that this shows that the model is actually identifying the characteristic signals of socioeconomic status in the brain but mistaking them for signals of IQ.

"It's incredible that they were able to build a predictive model based on socioeconomic status," said Beatriz Luna, a professor of psychiatry and pediatrics at the University of Pittsburgh who was not involved in the study. "We've always intuitively thought that socioeconomic status would have an impact, but the strength of this impact is still surprising."

Dosenbach pointed out that socioeconomic status is most strongly associated with the sensory and motor cortices, rather than with the frontoparietal regions responsible for higher cognitive functions. Previous studies have shown that these sensory and motor regions also respond to states of arousal, including sleep deprivation and stress. Therefore, these brain changes may reflect how children adapt to their environment. Poldrack said that he also observed a similar phenomenon when he scanned his own brain hundreds of times over the course of a year. The regions with the greatest changes in functional connectivity also occurred in the sensory and motor regions, and these changes were closely related to whether he had consumed caffeine.

The researchers said that this new study does not directly prove that socioeconomic status or other variables cause differences in brain function. But Marek believes that these findings can serve as a "road sign" to provide direction for future studies exploring specific mechanisms.

Poldrack said that this paper "raises as many questions as it answers." One of the unresolved questions is whether the association between socioeconomic status and brain morphology and function reflects an immediate physiological state or a long - term developmental effect. Poldrack pointed out that the correlation between socioeconomic status and functional connectivity is stronger than that between socioeconomic status and cortical thickness. Functional connectivity changes over time, while cortical thickness is relatively stable throughout life. This suggests that some of the phenomena detected in this study may be closer to a transient state rather than a permanent structural feature.

Marek said that in future research, he plans to track at which stage of life the association between socioeconomic factors and brain function first appears. Some studies have found that a measurable association between socioeconomic status and brain structure can be detected from birth to the age of 2. "We need to figure out when this association actually appears and what it means for the child's brain health outcomes later in life. These questions need further exploration, especially in a society like ours where the level of inequality has reached the current level," Marek said.

References

https://www.thetransmitter.org/brain-imaging/iqs-link-to-brain-structure-function-in-children-may-be-a-mirage/

This article is from the WeChat public account "Neural Reality" (ID: neureality). Author: Natalia Mesa. Republished by 36Kr with permission.