I'm actually one of the authors of this paper. I emailed natselrox about this, but figured I would also posted on here. Regarding this specific work, we could not rule out all pre-natal effects & influences. We were limited since we did not personally collect the data (it was part of a project from the US' National Institute of Health; additional info here: https://nihpd.crbs.ucsd.edu/nihpd/info/index.html
). The investigators who collected the data had a number of rigorous exclusion criteria (e.g., Low current height or weight, Intra-uterine exposures to substances known or highly suspected to alter brain structure or function, gestational age at birth of 37 weeks - 42 weeks; multiple birth; delivery by high forceps or vacuum extraction; maternal metabolic conditions (e.g., phenylketonuria, diabetes); low-birth weight pre-eclampsia; serious obstetric complication; general anesthesia during pregnancy/delivery; C- section for maternal or infant distress). These criteria were aimed at minimizing some of the confounds previous question suggested (but we must be honest & say we can not 100% rule out pre-natal factors). Some of my future work is aimed at assaying factors related to your questions (e.g., by doing longitudinal analyses of this sample to see if associations strengthen; or local data collection where we can collect more information about the household & early development).
In addition, the statistical models we used (regression) point to a linear relationship between household income and hippocampal volume (e.g., increasingly larger volume with higher household incomes). If we had done a group comparison (via a group t-test) where our measure of income wasn't continuous (and just compared a more affluent group to a less affluent group), nutritional deprivation would be a factor of greater concern (since it may be more common in less affluent households). Use of linear regression basically point to something more like "a dose effect" where a t-test would just look if one group was higher or lower. [Pardon the stats discussion, I wasn't sure of people's background].
I also ran post-hoc analyses (not in the paper, but related to the question) where even if you exclude the kids from the less affluent households (living in poverty where nutritional issues may be common) the relationship between household income and hippocampal volume is still significant. Folks can feel free to ask additional questions also.
Related to ideas of the paper and making a social point, my research centers on the neurobiological effects of/associations with early stress. I tend to share the views of someone like Gary Evans
, a professor at Cornell, who talks about poverty as chronic stress & cumulative risk.