Nonlinear relationship between early life stress exposure and subsequent resilience in monkeys.
Level 5 - mechanism / opinion, no new human data
Animal research (squirrel monkeys)
PubMed 31700103 · doi:10.1038/s41598-019-52810-5
What was done
Juvenile squirrel monkeys between 17 and 27 weeks of age were assigned to one of five experimental conditions representing varying doses of early life stress (0 to 3 stress elements): standard housing (No SI, 0 stressors), stress inoculation with continuous access to mother (SI + Mom, 1 stressor), stress inoculation without continuous access to mother (SI, 2 stressors), stress inoculation without mother plus alprazolam injections (SI + Alz, 3 stressors), or stress inoculation without mother plus vehicle injections (SI + Veh, 3 stressors). Subsequent anxiety-related indicators—including maternal clinging, novel object exploration, and cortisol responses—were assessed.
What was found
The abstract reports no numerical values, sample sizes, or effect estimates. Monitored qualitatively, monkeys exposed to 1 or 2 early life stressors subsequently exhibited fewer signs of anxiety (decreased maternal clinging, increased object exploration, and smaller cortisol increases) compared to unstressed control subjects. Monkeys exposed to 3 early life stressors did not differ on most measures from one another or from unstressed controls, indicating a nonlinear J-shaped relationship.
Why it matters
This study provides experimental animal evidence supporting the stress inoculation hypothesis, demonstrating that moderate early life stress fosters resilience compared to both stress absence and high stress.
Limits
The study was conducted in juvenile squirrel monkeys, limiting direct generalizability to humans. The abstract does not provide sample sizes, quantitative values, variance measures, or data on whether the observed resilience persists into adulthood.
Cited by
- supports Studies in squirrel monkeys by researchers at Stanford showed that exposure to moderate adversity early in life is a key factor in cultivating later-life resilience.