The team conducted in-depth interviews with 100 adults who had gone through episodes of major depressive disorder but had been asymptomatic for at least six months. Among the 49 participants who reported a history of parental loss during childhood, 23 had divorced or separated parents, eight had a deceased parent, five were abandoned, six had parents who were absent due to work, and seven had absentee parents for other reasons. The researchers inquired about each person's experiences with depression, and the severity and nature of the stressors involved.

Much like other researchers, Slavich and his collaborators observed that individuals who went through childhood trauma were more likely to get depressed when they encountered less serious ordeals as adults. They noticed a new twist, however: This effect was unique to respondents whose depressive episodes were prompted by interpersonal stress, such as the demise of a budding romance or the transfer of an office confidant. "Everyone in the study developed depression," Slavich adds, "but those who do not have a history of early parental loss were, on average, more resilient."

That small setbacks spark depression doesn't surprise UCLA researcher Steve Cole, whose own research has linked early-life difficulty with adult immune-system deficiencies. "The most toxic life stress involves social stress," he says, adding that what he found interesting is how Slavich's work on selective stress sensitization seems to reaffirm the work of psychoanalysts like Sigmund Freud. "Of course their detailed theories are not likely to be true," he says, "but this suggests they were right in that deeper historical patterns play a major precipitating role."

Queen's University psychology professor Kate Harkness says the Freudian "matching" of the nature of early and later stress is indeed intriguing and warrants future investigation. "It shows that early loss events sensitize individuals specifically and preferentially in the same loss domain," she says. Slavich agrees but has reservations: "The matching hypothesis is very interesting. But it's also possible that more severe types of early adversity like abuse may sensitize people to all forms of later life stress."

Still, the study's recognition of the power of seemingly trivial interpersonal loss is enough to advance depression interventions. Cole suggests that, since childhood heartbreak plays a major role in a patient's resilience to stress, psychologists should review more than a patient's immediate past when taking a patient history. They must be cautious when patients share stressful interpersonal loss events, adds Williams College psychology professor Catherine Stroud, no matter how inconsequential they seem. More specifically, Dienes says the finding bolsters the use of cognitive behavioral therapy (CBT), which is typically used to correct misguided and maladaptive beliefs, in depression treatment and prevention. "Cognitive distortions may arise from early feelings of abandonment," she says. "This research gives therapists a target to focus on for individuals at-risk for depression."