Multiple studies in both animals and humans show the importance of a mother’s love (or the unconditional love of any close person to a child) in a child’s brain development. A recent study shows that children with nurturing mothers had a substantially larger area of the brain called the hippocampus than children with less nurturing mothers. This is important because other studies have shown that the size of the hippocampus matters: People with large hippocampus area are more resilient and are more likely to be able to weather the stresses and strains of daily life. These observations come from experiments in animals and observational studies in humans.

(a) Is the amount of maternal nurturing one receives as a child positively or negatively associated with hippocampus size?

(b) Is hippocampus size positively or negatively associated with resiliency and the ability to weather the stresses of life?

(c) How might a randomized experiment be designed to test the effect described in part (a) in humans? Would such an experiment be ethical?

(d) Can we conclude that maternal nurturing in humans causes the hippocampus to grow larger? Can we conclude that maternal nurturing in animals (such as mice, who were used in many of the experiments) causes the hippocampus to grow larger? Explain.