The results on a sample of 769 brain-injured patients appear to be very dramatic: after a year a good recovery was achieved by 9.7% of those with fewer than 12 years of education, 30.8% with up to 15 years of education, and 39.2% with more than 16 years of education (p 0.001). The education effect held up in a logistic regression model controlling for age, sex, and injury- and rehabilitation specific factors. The authors concluded that educational attainment was a robust predictor of 1-year recovery even when adjusting for those other prognostic factors. A dose-response relationship was noted, with longer educational exposure associated with increased odds of recovery. This suggests that cognitive reserve could be a factor driving neural adaptation during recovery from traumatic brain injury.
Eric B. Schneider, Sandeepa Sur, Vanessa Raymont, et al. (2014) Functional recovery after moderate/severe traumatic brain injury: A role for cognitive reserve?
Not one of their references makes a mention of intelligence nor of cognitive epidemiology, so I was intending to make nothing more than a small but useful point that the differences between the groups go far beyond that of being exposed to education, or benefitting from education, in that they very probably largely reflect prior intelligence differences. So, for “cognitive reserve” read “intelligence”. Intelligent brains recover better.
However, there is an unremarked confound: the poorly educated slow recovering group are 52% white, the moderately educated better recovering group 72% white and the most educated fastest recovering group 82% white. This is because the white subjects were far more likely to have further education than Black and Hispanic patients. How do the authors deal with this?
Well, they report it in Table 1 but do not put it into the regression model as a factor. It would appear that if the patients had been classified by racial background there would be significant differences in their recovery rates. “White people recover faster from brain injury” is an equally supported conclusion to the “Educated people recover faster from brain injury” headline this paper has generated. It would have been better to have sorted this out and dealt with the race confound. One approach would have been to do the extra work to see if the patient’s scholastic attainments on national exams could have been traced. Since most of them probably sat some sort of exam at 12 or 13 years of age this would have been feasible. It would have provided an even more sensitive measure of ability.
The authors go through the chore of explaining the limitations of their study. The make the following points:
“First, it is important to acknowledge that educational attainment is a surrogate, and not a direct, marker of cognitive reserve. While available published research supports the construct of education as a marker of reserve, it remains unclear whether higher educational achievement is causatively linked to greater cognitive reserve, results from it, or both. Educational attainment itself is not solely reflective of intellectual or cognitive abilities. Motivation to succeed and self-discipline, as well as socioeconomic status, are likely also associated with higher levels of education and may have important roles in determining the degree of post-traumatic brain injury recovery.”
I would have liked them to have looked at Deary’s work on cognitive ageing for a background on the intelligence component in health.
This is not a bad study. There is a good sample size and good descriptive statistics. There is an unexplored confound with race, which could have been sorted out. Of greater importance is the even bigger lack of discussion about the link between cognitive “reserve” and cognitive “power” aka intelligence. Making that link could turn out to be very informative for both intelligence and for brain research.