EPI222_WTR16: Week 5 Assignment

Yes, I would say this mechanism of there being a sensitive window is relevant in humans. One behavior that may be analogous to maternal licking and grooming is exposure to language and vocabulary. For example, the Hertzman and Boyce article point to second language acquisition, showing that there seems to be a sensitive window in which there is optimal second language acquisition. After a certain age, it becomes more difficult to acquire a second language to the fluency of a native speaker of that language. Second language aside, there is evidence that exposure to a wide array of vocabulary during sensitive and early developmental periods is associated with higher cognitive functioning and verbal abilities later in life. Research by Hart and Risley show that children who heard more words by the 4^th birthday, compared to those who heard fewer words, were better prepared for school, and better vocabularies, and performed better on exams. The research also shows that if this developmental period is “missed,” it cannot necessarily be “made up.” Parental behavior may be associated with exposure to vocabulary and words. If parents are unable to read to their children or converse with them because of lack of time, resources, etc., that would then have downstream effects on the child’s later verbal abilities.

2. The cumulative effects model is not necessarily inconsistent with Weaver’s findings. Weaver’s findings are focused more on a critical period, but in line with Gruenewald’s argument, those who miss critical periods are likely to be qualitatively different than those who do not miss the critical period. In that sense, it would make sense that one vulnerability is associated with other vulnerabilities.

3. I believe that gene by environment interactions can contribute to major disparities to a relatively large extent. This may be one of the major reasons why there are such notable racial/ethnic, socioeconomic, and geographic disparities in cardiovascular risk factors such as obesity. Individuals may be genetically vulnerable to developing obesity, and the environment in which people live can contribute to becoming obese. I think this is a good example of where developmental programming is also relevant. I know I am not the most eloquent in describing this, but research shows that individuals who were exposed to stressful environments in utero (e.g., lack of nutrition, toxins) may have slower fetal growth; when these babies are born, various environmental aspects, such as access to a high fat diet, have more negative impacts on these babies. Then this eventually contributes to development of chronic disease later in life.

Re: Week 5 Assignment

by Maria Glymour - Tuesday, February 2, 2016, 9:55 AM

Thanks Jin for this thoughtful response. Indeed, I think language development is one of the nicer examples of a sensitive period. Your point that "one vulnerability is associated with other vulnerabilities" is really a central problem in doing causal research on the sources of inequalities. We need to do rigorous research to identify what we could change/intervene upon to improve health outcomes and eliminate inequalities, but distinguishing between the effects of intervening at age 2 years versus age 12 years turns out to be very tricky. The fact is that children who are in disadvantaged settings at age 2 are usually also in disadvantaged settings at age 12 (and also age 42, incidentally), so it's very tough to tell observationally when an intervention could be beneficial. This leads to a lot of key debates in the field: how critical is it to get interventions to very young children? Is there still a benefit of intervening to help older children or even adults. Some argue no - it's a waste of money and effort after a certain age because it's very unlikely to have a large benefit.