Razib calls my attention to this new Nature study on the genetic variation underlying the stress response. The researchers focused on neuropeptide Y, an endogenous anxiolytic (it’s like an anti-anxiety drug naturally produced by the brain) which is released in response to stress. They focused on a single nucleotide polymorphism (aka SNP) which “alters NPY expression in vitro and seems to account for more than half of the variation in expression in vivo.”
The pertinent question, of course, is how they measured variation in vivo. The researchers used a few different, and quite interesting, techniques. The first method (the Pittsburgh sample) involved showing people “threat-related facial expressions” and measuring amygdala activity with fMRI. They found that “amygdala activation was higher in individuals with the low-NPY expression,” although it’s worth pointing out that this only accounted for 9 percent of the variance in fMRI response.
The second test of stress involved measuring “endogenous opioid release” with PET in response to a painful stimuli. These results were quite interesting: “highly expressed NPY diplotypes predicted significantly higher levels of stress-induced opioid system activation” throughout the brain, so that 37 percent of the variance in opioid release in the posterior insular cortex was due to the NPY diplotype. In other words, the brains of the lucky people with this SNP released more painkillers in response to pain. In theory, at least, this means that the experience of pain was less stressful. (One thing I don’t understand, however, is why these endogenous opioids didn’t correlate with a reduced pain response: according to the data, the NPY diplotype only accounted for 3 percent of the variance in subjective pain.)
Obviously, this study has far-reaching ramifications. The regulation of stress is a critically important function of the brain, and the breakdown of this process has been linked to everything from depression to neurogenesis to PTSD. It’s pretty astonishing to think that a significant amount of the variation of the stress response is tied to a few basepairs of DNA. The next step it to see if this slight genetic variation correlates with various types of mental illness. Are soldiers with low-expressions of NPY more likely to get PTSD? Does having lots of NPY in the brain make people less likely to choke under pressure? Are the different levels of NPY expression evenly distributed in various socio-economic strata? Etc, etc.