The task given to participants in an Oxford University depression study sounds straightforward. After investigators read them a cue word, they have 30 seconds to recount a single specific memory, meaning an event that lasted less than one day.
Cues may be positive (“loved”), negative (“heartless”) or neutral (“green”). For “rejected,” one participant answered, “A few weeks ago, I had a meeting with my boss, and my ideas were rejected.” Another said, “My brothers are always talking about going on holiday without me.”
The second answer was wrong — it is not specific, and it refers to something that took place on several occasions. But in studies under way at Oxford and elsewhere, scientists are looking to such failures to gain new insights into the diagnosis and treatment of depression. They are focusing not on what people remember, but how.
The phenomenon is called overgeneral memory, a tendency to recall past events in a broad, vague manner. “It’s an unsung vulnerability factor for unhelpful reactions when things go wrong in life,” said Mark Williams, the clinical psychologist who has been leading the Oxford studies.
Some forgetting is essential for healthy functioning — “If you’re trying to remember where you parked the car at the supermarket, it would be disastrous if all other times you parked the car at the supermarket came to mind,” said Martin Conway, a cognitive psychologist at the University of Leeds in England. But, a chronic tendency to obliterate details has been linked to longer and more intense episodes of depression.
Now researchers at Oxford, Northwestern University in Illinois and other universities are conducting studies with thousands of teenagers to determine whether those with overgeneral memory are more likely to develop depression later on. If so, then a seemingly innocuous quirk of memory could help foretell whether someone will experience mental illness.
“Based on everything we know of memory specificity and depression, there’s a good chance we will find these effects,” said Dirk Hermans, a research psychologist at the University of Leuven in Belgium who collaborates with Dr. Williams.
There are already some clues in this direction. In lab experiments Dr. Williams has induced an overgeneral style in subjects by coaching them to recall types of events (“when I drive to work”) rather than specific occasions (“when I drove to work last Saturday”). He found they were suddenly less able to solve problems, suggesting that overgeneral memory is capable of producing one symptom of depression.
And an unusual paper suggests that overgeneral memory is a risk factor for post-traumatic stress disorder. Scientists at the University of New South Wales in Sydney, Australia, assessed 46 firefighters during their initial training and again four years later, when all had experienced traumatic events like seeing comrades injured or killed. Those who could not recall the past in specific detail during the first assessment were much likelier to have developed the disorder by the later one.
“People with P.T.S.D. tend to ruminate at a very categorical, general level about how unsafe life is, or how weak I am, or how guilty I am,” said the lead author, Richard Bryant. “If I do that habitually and then I walk into a trauma, probably I’m going to be resorting to that way of thinking and it’s going to set me up for developing P.T.S.D.”
Dr. Williams stumbled across overgeneral memory by chance in the 1980s. He had asked research subjects to write down the memories elicited by certain cues, and when they left the page blank he thought he had given unclear instructions. Soon he began to wonder about the significance of the omissions.
Usually people seeking a particular memory traverse a mental hierarchy, Dr. Williams said. They begin by focusing on a general description (“playing ball with my brother”) and then narrow the search to a specific event (“last Thanksgiving”). Some people stop searching at the level of generality, however and are probably not conscious of having done so.
This is sometimes a helpful response, which is perhaps why overgeneral memory exists in the first place — it can be a useful way to block particular traumatic or painful memories. Researchers at Leuven discovered that students who did poorly on exams and were more specific took longer to recover from the disappointment than those who were more general. The overgeneral students thought less about the details of what happened and so fared better, at least in the short term.
Similarly, overgenerality has been found to be prevalent in Bosnian and Serbian teenagers exposed to the traumas of war. “Some people will discover at a certain stage that being overgeneral is a way of dampening emotional effects,” Dr. Hermans said.
But these researchers say problems can arise when overgenerality becomes an inflexible, blanket style.
Without detailed memories to draw upon, dispelling a black mood can seem impossible. Patients may remember once having felt happy, but cannot recall specific things that contributed to their happiness, like visiting friends or a favorite restaurant.
“If you’re unhappy and you want to be happy, it’s helpful to have memories that you can navigate through to come up with specific solutions,” Dr. Williams said. “It’s like a safety net.”
Some experts think such insights could also be helpful in treating depression. For example, Spanish researchers have reported that aging patients showed fewer symptoms of depression and hopelessness after they practiced techniques for retrieving detailed memories.
“When we have a disorder like depression, which is so common and so disabling for so many people, we need to increase the tools in our tool kit,” said Susan Mineka, a clinical psychologist working on a study by Northwestern University and the University of California, Los Angeles, that is testing for depression and anxiety risk factors, including overgeneral memory. “If we could change their overgeneral memory, maybe that would help even more people stay better for longer.”
Dr. Williams has found that specificity can be increased with training in mindfulness, a form of meditation increasingly popular in combating some types of depression. Subjects are taught to focus on moment-to-moment experiences and to accept their negative thoughts rather than trying to avoid them. It may help by making people more tolerant of negative memories and short-circuit the impulse to escape them, which can lead to overgenerality.
Meditation means that for some, the past is no longer such a heavy burden.
“I always tried to forget the past, the very bad past that made me depressed when my husband died,” said Carol Cattley, 76, who attended a mindfulness course here taught by Dr. Williams. “I’m much more interested in it now.”
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