Ned Kalin and his colleagues here at the University of Wisconsin have made the interesting observation that increased brain activity in the amygdala (not inheritable) and anterior hippocampus (inheritable) of young monkeys can predict anxious temperament in young monkeys, leading Kalin to suggest that "that young children who have higher activity in these brain regions are more likely to develop anxiety and depression as adolescents and adults, and are also more likely to develop drug and alcohol problems in an attempt to treat their distress." The study looked at 238 young rhesus monkeys from a family of more than 1500 lab-raised monkeys with well-documented pedigrees. By analyzing the family connections among the young monkeys, which ranged from siblings to distant cousins, the finding was that an anxious temperament was partly heritable, accounting for about 36% of the variability in individual monkeys' responses on a human intruder test (as measured by the reduction in movement and vocalization and increase in stress hormone levels). Elevated responses in the hippocampus were heritable (accounting for about half of individual variability), whereas the elevated responses in the amygdala were not.
Figure from paper - Anxious monkeys show elevated activity in the amygdala (left) and anterior hippocampus (right), but the effects of heredity seem to act more on the hippocampus.