In Superintelligence Bostrom writes:

‘Our individual cognitive capacities can be strengthened in various ways, including by such traditional methods as education and training. Neurological development can be promoted by low-tech interventions such as optimizing maternal and infant nutrition, removing lead and other neurotoxic pollutants from the environment, eradicating parasites, ensuring adequate sleep and exercise, and preventing diseases that affect the brain. [...]  “According to the World Health Organization in 2007, nearly 2 billion individuals have insufficient iodine intake (The Lancet 2008). Severe iodine deficiency hinders neurological development and leads to cretinism, which involves an average loss of about 12.5 IQ points (Qian et al. 2005). The condition can be easily and inexpensively prevented though salt fortification (Horton et al. 2008).’[1]

Summary

Here, I propose launching a new philanthropic cause area and academic field: ‘Developmental Cognitive Neuroepidemiology’ (DCN).

DCN combines the following two fields:

1. Neuroepidemiology, 'a branch of epidemiology involving the study of neurological disease and its determinants and frequency in human populations.' Put simply, Neuroepidemiology is the study of what causes brain disease and how many people are affected and how badly. For instance, alcoholism sometimes causes brain damage and reduced IQ; studying the causes of alcoholism, finding out how many alcoholics there are, how many of them have brain damage and how badly they are affected would be an example of neuroepidemiology. Another example is one paper that ~17 million IQ points have been lost due to exposure to pesticides.[5]
2. (Human) Developmental cognitive neuroscience, is 'an interdisciplinary scientific field devoted to understanding psychological processes and their neurological bases in the developing human. It examines how the mind changes as children [and young adults] grow up, interrelations between that and how the brain is changing, and environmental and biological influences on the developing mind and brain.'

And so, in essence, DCN studies what causes brain disease—widely construed to also include suboptimal brain development and cognitive function—in children and young adults (eventually also across the whole life span), and how many are affected and how badly.

The field’s aim might be to elevate optimal neurodevelopment to a similar rank on the policy agenda as physical development. I motivate this by examining the importance and scale of the problem. I focus on reviewing some previous work trying to quantify the scale of what might cause suboptimal cognitive development. I start by giving some concrete examples

Sometimes IQ loss during development is very cost-effective to prevent, e.g. preventing iodine deficiency [2],[3] (supplementation or fortification of staple foods 100 additional years per $100 spent on supplements, and an increase in ~1k-2k IQ points (7-10 IQ points for ~185 children). This ~100 IQ points per ~$1 spent. Each point increase in IQ test scores raises income by ~$100-$1000 per year after holding a variety of factors constant and so benefit-cost ratios of select interventions might be very high. Increasing IQ from current mean (100) to the top 2 percent of society (130) increases wages by ~$10k,[4] and so raising the IQ of 100M people would to such an extent would raise world GDP by at least $1T.

Importance / Scale

Intelligence and healthy cognitive neurodevelopment is an important prerequisite for a  flourishing life and suboptimal neurodevelopment might also have high social costs.

For instance, Caplan argues that education raises support for capitalism, free markets, globalization, civil liberties and tolerance, and reduces racism and sexism. Correcting for intelligence cuts education’s impact by ~1/3.[5]

As a result of suboptimal child neurodevelopment we likely lessen the effectiveness of education for hundreds of millions or even billions—I review the evidence below. In contrast, early childhood education has mixed evidence.[6] However, we spend a lot of money on early childhood education, but very little on cognitive development. This might be because education is much less controversial and that the idea that intelligence is fixed to a substantial extent in early childhood or in utero is uncomfortable and controversial (as it might be conflated with genetic differences in intelligence between cultures).

Suboptimal child neurodevelopment might have drastic general equilibrium effects as well. People with low IQs might not be able to understand and answer conditional hypothetical questions [7] (e.g. ‘"How would you have felt yesterday evening if you hadn't eaten breakfast or lunch?" "What do you mean? I did eat breakfast and lunch." "Yes, but if you had not, how would you have felt?" "Why are you saying that I didn't eat breakfast? I just told you that did." "Imagine that you hadn't eaten it, though. How would you have felt?" "I don't understand the question.").

Specific Examples of some potentially highly cost-effective public health problems that cause suboptimal neurodevelopment

Consider the literature on the 'fetal origins hypothesis' and child development, where early environment affects cognitive development and later life outcomes.[8] Some of the effect sizes are downright incredible (not using this term lightly) and its implications might be 'big, if true' and so deserve further study.

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