After Janice Van Wagner's mother died of breast cancer two years ago, her sense of loss was overwhelming.
"I was devastated," said Van Wagner, 34, of Los Angeles. "I felt like a piece of me had gone missing. It was like I was split in two."
While most people grieve when someone close to them dies, the emotional intensity tends to recede with time. But for some, like Van Wagner, their pain persists, sometimes for months or even years, often making it impossible to resume a normal life.
"I was kind of stuck in a repetitive thinking about the suffering that she went through in the last month of her life and the last few weeks," Van Wagner said.
This unrelenting form of mourning, which affects an estimated 10 to 20 percent of people who have lost someone close, is gaining recognition as a distinct psychological syndrome known as "complicated grief."
Now, studying it with brain scanning technology, researchers have found a biological clue that appears to help confirm the existence of the syndrome and explain why it happens.
For the study, Mary-Frances O'Connor of UCLA and her colleagues conducted functional magnetic resonance imaging (fMRI) on 11 women experiencing complicated grief, including Van Wagner, and 12 others who grieved more normally. All were tested after the death of a mother or sister from breast cancer.
During the scans, which show what parts of the brain are active at a given moment, each woman was asked to look at a picture of her lost loved one — with words superimposed to remind her of the death — or at similar pictures of strangers.
"I wanted to know if there is something different in the brain when people are processing their grief in those people who are adapting well and those who are not," O'Connor said. "The question was: Are their brains processing their grief differently?"
In all the women, the parts of the brain involved in physical and emotional pain activated only when they saw the pictures of their loved ones. But in the women experiencing complicated grief, another area also lighted up.
Called the nucleus accumbens, it is part of the brain's reward system, the researchers reported this month.
One of the hallmarks of complicated grief, however, is a persistent sense of longing for the lost one and a tendency to conjure up good feelings of that person.
"It's an intense feeling of wanting that person back," Van Wagner said.
Because the nucleus accumbens is involved in expecting a reward, this might explain why people suffering complex grief are unable to move on, researchers suspect.
"This is the part of the brain involved in knowing that you want something," O'Connor said. "When people who are not adjusting well are having these sorts of thoughts about the person, they are experiencing this reward pathway being activated. They really are craving in a way that perhaps is not allowing them or helping them adapt to the new reality."
The same brain system is involved in other powerful cravings, such those that afflict drug addicts and alcoholics.
"One reason they are stuck is they are getting something pleasurable about thinking about and immersing themselves in memories of the deceased," said Holly Prigerson, an associate professor of psychiatry at Harvard Medical School. "It's like they're addicted to the happy memories."
The findings could help explain why drugs used to treat depression are generally ineffective for complicated grief: They affect a different part of the brain.
In addition, the findings could provide insights that could lead to improved psychotherapy for complicated grief, which has proved highly resistant to therapies used for depression.