Open problems · P9
Blunted reactivity near the edge
In MIDUS, people near an edge (high allostatic load, high blood pressure, diabetes) do not settle further from rest after a laboratory stress task than others measured in the same wave, once response size is allowed for. In heart rate, high allostatic load and diabetes go with a smaller response; in blood pressure, high blood pressure goes with a larger one, clearest in the earlier wave. A one-dimensional valley model predicts a larger displacement and a slower return. Does a system near an edge lose gain, its sensitivity to input, rather than only the depth of its valley?
Why it matters
If what changes near an edge is a loss of gain rather than a flattening of the valley, the model of the stress response needs another dimension, and recovery time alone is the wrong early-warning measure. An established literature already links blunted cardiovascular and cortisol reactions to poor health.
What exists
- Within-wave comparisons of response and of shortfall at equal response by edge group in MIDUS, in heart rate and systolic pressure, with equivalence tests (Mountainside).
- Reviews of blunted reactivity and health: Phillips, Ginty and Hughes (International Journal of Psychophysiology 2013); Carroll and colleagues (Neuroscience and Biobehavioral Reviews 2017); Lovallo (Biological Psychology 2011).
- The allostasis model with load and capacity as two coupled states (Allostatic load).
- Other cohorts with a repeated laboratory challenge and biomarkers.
A first step
Use the two-variable load and capacity model to ask whether the measured variable responds less to the same challenge as capacity falls toward the fold. If it does not, write down the smallest extension in which it does (for example, a second, slow variable that saturates the response), derive what it predicts for response and recovery together, and check those predictions against the MIDUS group results and a second cohort.