What are the effects of stress & adversity on the brain that affect well-being? A recent review by Davidson & McEwen in Nature Neuroscience (“Social influences on neuroplasticity: stress and interventions to promote well-being”) explores this question. One interesting aspect about research on the relationship between the brain and “happiness” or “well-being” is how we operationally define these constructs. Most of us “know” what “happiness” is - or do we? What about well-being? Interestingly, Davidson & McEwen do not define well-being in this review; they assume we all agree on what it is.
Assuming that we all agree on what well-being is, the review summarizes animal and human research on the effects of stress on the brain and on social/emotional functioning. We know that chronic stress reduces dendritic branching in the medial prefrontal cortex and hippocampus, while it increases branching in orbitofrontal cortex and amygdala. These regions are important for emotional and social behavior, and Davidson & McEwen propose that they are important for well-being. The effects they summarize on dendritic branching in these regions are reversible, especially in children, so perhaps therapies that lead to a better sense of well-being are, at least in part, acting through these brain regions/circuits.
Early life stress is a particularly extraordinary example of how experience influences brain structure and function in ways that can have devastating effects on how a child is able to function in the world. But the hopeful message of this review is that, even though the horrible stress of child abuse has detrimental effects on a child’s brain, these effects should be at least partly reversible, based on animal research. The positive effects found following intervention programs that address emotional and social functioning in school-aged children reflect changes in brain structure and function.
A recent article in PNAS by Claudia Buss and colleagues [Maternal cortisol over the course of pregnancy and subsequent child amygdala and hippocampus volumes and affective problems] reports that mother’s stress during pregnancy has long-term consequences on the child’s brain development and subsequent emotional development.
Indications of this has been apparent from the animal literature for a long time, but this longitudinal study periodically assessed salivary cortisol in pregnant women and followed the children until age 7, when the researchers took MRIs of the children’s brains and assessed their affective problems. From the MRIs, amygdala and hippocampal volumes were calculated. Higher cortisol levels in the mothers during early pregnancy, but not later pregnancy, was associated with larger amygdala volumes and greater affective problems in girls but not boys. The affective problems were mediated by amygdala size.
This study appears to be the first that shows this relationship in humans. When the mother experiences stress, cortisol is released her body and can enter the fetus. Through this association, brain structure is affected. In adults, the amygdala is implicated in mood and anxiety disorders and in emotional behavior — for example, when a person is depressed, cortisol may affect amygdala activity which may in turn influence cognitive and emotional processing. Perhaps this process (prenatal stress affecting amygdala structure) contributes to the increased rates of depression in children from low socioeconomic households.
But why only in girls? That’s very interesting.